Method for predicting blue crab molting based on behavior and morphological characteristics

Abstract

The invention discloses a method for predicting blue crab molting based on behavior and morphological characteristics. The method comprises the following steps: identifying a molting early stage and a molting adjacent stage, determining 12-15 days before molting when at least three quantitative characteristics of five molting early stages are satisfied and the time is not less than 3 days, determining molting within 1-2 days when the characteristics of four molting adjacent stages are satisfied, and matching hierarchical regulation and control measures. According to the method for predicting the molting of the blue crabs based on the behavior and morphological characteristics, a standardized instrument is adopted to measure the quantitative characteristics, the prediction accuracy rate reaches 97.5% and is improved by 66.7% compared with 58.5% of a traditional method, the molting success rate can reach 96.0%, and the death rate is reduced to 4.0%; the early warning window is prolonged by more than 500%, and the method is suitable for various blue crabs and is beneficial to improving the initiative and benefit of breeding management.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of aquaculture, and particularly relates to a method for predicting the molting of blue crabs based on behavior and morphological characteristics. BACKGROUND

[0002] Blue crabs, including several varieties such as Archaebuthus and Charybdis, are important economic crustaceans in the southeast coastal areas of China. They are delicious and nutritious, and have both food and economic value, making them one of the core categories of aquaculture. Molting is a key physiological process for the growth and development of blue crabs, and it occurs throughout their entire life cycle. Blue crabs grow in size, update their shells, and repair damage through molting, and the success rate of molting directly determines the survival rate and yield of aquaculture. However, the molting period of blue crabs is extremely sensitive to the external environment, and is easily affected by water quality, feed, and pests. If the molting opportunity is not accurately predicted and targeted management measures are not taken, molting failure, mutual cannibalism, or infection of diseases may occur, causing significant economic losses to the aquaculture industry.

[0003] There are many core difficulties in predicting the molting of blue crabs. First, the molting process is regulated by multiple factors such as physiological rhythms and environmental parameters, and the molting cycle fluctuates greatly due to differences in growth stage and individual differences. Second, the physiological changes in the pre-molting and adjacent stages are hidden, and traditional visual observation cannot capture subtle changes in morphological and behavioral characteristics. Third, the dynamic nature of the cultivation environment (such as fluctuations in water temperature and salinity) further increases the uncertainty of predicting the molting opportunity.

[0004] Current industry molting prediction technologies can be divided into three categories. The first is the experience judgment method, which relies on the observation of blue crab body color, feeding activity, and other macro characteristics to make predictions. This method is greatly influenced by subjective experience, has low precision, and cannot achieve early warning. The second is the single index monitoring method, which monitors water temperature, salinity, or a single morphological index (such as shell hardness) to make predictions. This method ignores the coordinated changes in blue crab physiology and behavior, resulting in a high rate of misjudgment. The third is the instrument monitoring method, which uses water quality monitors and image equipment to monitor a single parameter. Although this method improves the objectivity of the data, it is difficult to fully reflect the physiological mechanisms of molting because it does not establish a multi-index correlation model, and the timeliness of the warning is insufficient. The above methods all have the defects of low precision, delayed warning, or narrow application range, and cannot meet the needs of large-scale aquaculture for precise management during the molting period.

[0005] The present application proposes a method for predicting the molting of blue crabs based on behavior and morphological characteristics, which solves the core problems of low precision and poor timeliness of traditional methods through multi-dimensional index fusion and quantitative judgment, and provides technical support for fine management of blue crabs during the molting period. SUMMARY

[0006] The present application aims to at least solve one of the above technical problems in the prior art. To this end, the purpose of the present application is to provide a method for predicting the molting of blue crabs based on behavioral and morphological characteristics. The method of the present application can determine the pre-molting period (12-15 days before molting) and the imminent molting period (1-2 days before molting) of blue crabs. Molting is a complex physiological metabolic process that requires a complete cycle of "energy accumulation - new shell construction - old shell shedding": 12-15 days before molting, to meet the energy needs of new shell synthesis and body growth, blue crabs will actively increase their food intake and prefer high-protein bait, while blood lymph accumulates in the joint of the appendage, causing joint swelling and color change. The carapace appears to have a raised edge due to the development of the new shell, the abdominal umbilical setae grow and change color with physiological changes, and the abdomen appears to be raised due to water accumulation and space occupation by the new shell. In the 1-2 days before molting, the physiological state of the blue crab changes dramatically. First, it rests to accumulate energy, then the activity frequency increases significantly and the appendages stand up to find a support point for molting as the old shell loosens and the new shell is about to break through. The hardness of the specific part of the plastron decreases due to the redissolution of calcium carbonate in the old shell, the breathing rate increases to meet the high metabolic demand, and the body surface is cleaned of attachments and the old shell joint is loosened through wiping behavior to prepare for the final molting. By quantifying and combining these key physiological signals throughout the molting cycle, false positives caused by environmental fluctuations or individual differences can be avoided, and accidental changes can be filtered out by setting "multiple feature satisfaction + continuous duration", thereby achieving accurate positioning of the molting stage.

[0007] To achieve the above-mentioned purpose, the technical solution adopted by the present application is: In a first aspect of the present application, a method for predicting the molting period of blue crabs is provided, the molting period including the pre-molting period and the imminent molting period; the method comprising the following steps: obtaining the behavioral data and morphological data of the blue crabs, and predicting the pre-molting period and the imminent molting period of the blue crabs; the behavioral data including the feeding behavior, activity frequency, breathing rate, and wiping behavior of the blue crabs; the morphological data including the appendage joint features, carapace edge features, abdominal umbilical setae length, abdominal umbilical color, abdominal morphological changes, and shell hardness of the blue crabs.

[0008] In some embodiments of the present application, the abdominal morphological changes include changes in the vertical distance between the central part of the plastron and the posterior edge of the carapace.

[0009] In some embodiments of the present application, the wiping behavior refers to the action of the blue crab scratching the joint between the plastron and the carapace with the chelae, as well as the cleaning action of the steps on the body surface attachments.

[0010] In some embodiments of the present application, the prediction of the pre-molting period is based on the feeding behavior, appendage joint features, carapace edge features, abdominal umbilical setae length, abdominal umbilical color, and abdominal morphological changes of the blue crabs; the pre-molting period of the blue crabs is 12-15 days before molting.

[0011] In some embodiments of the present application, when the mud crab satisfies at least three of the following (1)-(5), it is predicted that the mud crab enters the pre-molt stage; (1) The daily food intake of the mud crab is increased by 20% or more compared to the normal baseline level, and protein is preferentially ingested; the normal baseline level is the average daily food intake of the mud crab 7-20 days after molting; the protein includes at least one of fish, shrimp and shellfish; (2) The diameter of the appendage joint is increased by 3% or more compared to the non-molt stage; at the same time, the skin color value at the joint is reduced by 10% or more compared to the normal area; the normal area is the adjacent area of the joint; (3) The carapace of the mud crab forms a continuous raised line at the posterior and lateral edges, and the width of the raised line is greater than or equal to 0.5 mm; (4) The length of the setae on the outer edge of the umbilicus of the mud crab is increased by 20% or more compared to the non-molt stage, and the umbilical color L value is ≥80 and b value is 20-30; the umbilical color L value and b value are obtained using the CIELab color space; (5) The vertical distance between the central part of the sternum and the posterior edge of the carapace is increased by 5% or more compared to the non-molt stage with similar body width; The non-molt stage is 7-15 days after molting.

[0012] In some embodiments of the present application, the protein includes bait with a protein content of ≥40%.

[0013] In some embodiments of the present application, the non-molt stage is the stable stage of the mud crab after molting; the daily food intake of the mud crab in the non-molt stage fluctuates by no more than ±5%.

[0014] In some embodiments of the present application, the preferential ingestion of protein includes a higher priority for the mud crab to ingest fish, shrimp and shellfish than other bait such as organic detritus, low-protein algae, etc.

[0015] In some embodiments of the present application, the joint diameter is measured using an electronic caliper with an accuracy of 0.01 mm, the measurement site is the junction of the cheliped coxa and the body segment, the junction of the pedal coxa and the body segment, each site is measured 3 times, and the average value is compared with the average value of the corresponding site in the normal state to calculate the swelling rate.

[0016] In some embodiments of the present application, the color value is measured using a standard color chart (GB / T 22290-2008), and the measurement is performed under natural light conditions (light intensity 5000-10000 lx); the measurement area is the swollen part of the appendage joint and the adjacent normal skin area; each area is measured 3 times to obtain the average value.

[0017] In some embodiments of the present application, the convex line width is measured by a digital vernier caliper with an accuracy of 0.01 mm, and the measurement position is the midpoint of the carapace rear edge and the midpoint of the left and right lateral edges, a total of 3 positions, and the arithmetic mean of 3 measurements perpendicular to the line direction is taken as the final width value.

[0018] In some embodiments of the present application, the length of the bristles is measured by a high-precision image measuring instrument, including the following steps: fixing the blue crab sample on a sample stage, collecting a high-definition image of the bristle area outside the navel, converting pixels to actual length using a standard calibration ruler, and measuring the length along the main axis of the bristles, with a measurement accuracy of ±0.1 mm.

[0019] In some embodiments of the present application, the measurement method of the navel color is as follows: an image of the navel area is collected under a standard light source, and the L value and b value are extracted using the CIE Lab color space; when L≥80 and the b value is in the range of 10-20, it is determined to be pure white, and when the b value rises to the range of 20-30, it is determined to be gradually changing to pale yellow.

[0020] In some embodiments of the present application, the standard light source is obtained using a standard light source box.

[0021] In some embodiments of the present application, the vertical distance between the central part of the plastron and the rear edge of the carapace is measured by a digital height gauge with an accuracy of 0.01 mm, and the blue crab is placed on a horizontal experimental table with the plastron facing down and naturally resting, and the vertical distance between the highest point of the central part of the plastron and the lowest point of the rear edge of the carapace is measured.

[0022] In some embodiments of the present application, the molting approaching period is predicted based on activity frequency, shell hardness, breathing frequency, and wiping behavior, and the molting approaching period is 1-2 days before molting.

[0023] In some embodiments of the present application, the shell hardness includes the hardness of the plastron part below the longest sawtooth on both sides of the carapace.

[0024] In some embodiments of the present application, when the blue crab enters the pre-molting period, and all of the following (1)-(4) are met, it is predicted that the blue crab enters the molting approaching period. (1) After the blue crab has been resting for 24-48 hours, the number of movements per hour increases by 300% or more compared to the resting period, and the number of times of standing with appendages per hour is not less than 5 times, each lasting not less than 15 seconds; (2) The hardness of the plastron part below the longest sawtooth on both sides of the carapace decreases by 20% or more compared to non-molting individuals; (3) The number of times of opening and closing the gill cover is counted, and the breathing frequency of the blue crab reaches 13-16 times per minute; (4) The number of times of the action of scraping the joint between the carapace and the sternum with the chelae per hour is not less than 20 times, and each time lasts not less than 10 seconds, and the cleaning action of the steps is accompanied by the cleaning action of the body surface, and the cumulative length of the wiping behavior per day is not less than 5 minutes.

[0025] In some embodiments of the present application, the hardness of the sternum site is measured by a Shore hardness tester (type A), the instrument is calibrated before measurement, the probe is perpendicular to the surface of the sternum during measurement, a pressure of 1N is applied, each measurement site is measured for 3 times, and the average value is compared with the average value of the hardness of the same site of the non-molt stage individual to calculate the hardness reduction rate.

[0026] In some embodiments of the present application, the straight-up state of the appendage is that the steps or chelae vertically support the body, and the cephalothorax is lifted off the bottom surface.

[0027] In some embodiments of the present application, the activity frequency, the number of times of straight-up of the appendage, the number of times of digging and wiping actions are recorded by a high-definition camera (frame rate ≥ 30 fps) for continuous shooting, the shooting time is not less than 1 hour, and the image analysis software is used to count the relevant behavior parameters; the breathing frequency is counted by manually counting the number of times of opening and closing of the gill cover, each counting time is 1 minute, and the counting is repeated for 3 times with an interval of 5 minutes, and the average value is taken.

[0028] In some embodiments of the present application, the non-molt stage blue crab is a healthy blue crab with a body width difference of ≤5% and a body weight difference of ≤10% from the blue crab to be tested, and which is in a stable period of 7-15 days after molting.

[0029] In some embodiments of the present application, the blue crab includes Aratus pisonii, Scylla serrata, Scylla olivacea, Scylla tranquebarica or a hybrid individual thereof.

[0030] In a second aspect of the present application, a breeding method for a blue crab in a pre-molting stage is provided, and the method comprises the following steps: after the pre-molting stage is predicted by using the method of the above aspect, any one or several of the following steps (1)-(5) are performed: (1) increasing the light shielding rate of the environment to 60-70%; (2) increasing the calcium ion concentration of the water body to 400-500 mg / kg, and maintaining the dissolved oxygen at 5.5-6.0 mg / L; (3) increasing the feeding frequency to 3-5 times, and the single feeding amount is 3-4% of the body weight of the blue crab, and the feeding includes feeding feed from at least one source of fish, shrimp and shellfish; (4) adjusting the light intensity to 500-1000 lx; (5) controlling the ammonia nitrogen of the water body to be ≤0.1 mg / L, and the nitrite to be ≤0.05 mg / L.

[0031] In a third aspect of the present application, a method for culturing a crab in a molting approaching stage is provided, the method comprising the following steps: after predicting the approaching molting stage using the method of the above aspect, performing any one or more of the following steps (1)-(6): (1) increasing the water temperature to 26-28℃; (2) adjusting the light intensity to 100-200 lx; (3) adjusting the light cycle to 8-10 hours of light and 14-16 hours of darkness; (4) adding 0.5-1 g / m 3 vitamin C and 0.1-0.5 g / m 3 EDTA-2Na to the water body according to the proportion of the usage amount and the volume of the water body; (5) adjusting the dissolved oxygen in the water body to 6.5-7.5 mg / L; (6) stopping feeding the bait.

[0032] In some embodiments of the present application, the step of increasing the water temperature to 26-28℃ comprises increasing the water temperature by 2-3℃ at a rate of 0.2-0.4℃ per hour, and finally stabilizing at 26-28℃.

[0033] The present application has the following advantages: The present application provides a method for predicting the molting of blue crabs based on behavior and morphological characteristics, which has significant advantages over traditional techniques, as follows: I. Comprehensive index system: Simultaneously monitor the swelling and color change of the appendage joints, the protrusion of the carapace edge, the slight bulging of the abdominal shield, the softening of the tissue in specific areas, the accelerated breathing rate, and the wiping behavior, covering the complete physiological change chain from the pre-molting stage to the approaching stage; Abandon the traditional single index or visual observation judgment method; II. Quantitative determination criteria: Replace subjective judgment with quantitative indicators such as feeding behavior quantitative analysis, standard color chart, width value, swelling rate, and gill cover opening frequency, to improve prediction accuracy. Each feature is measured using standardized tools such as precision 0.01 mm calipers and GB / T22290-2008 standard color chart. In the cultivation test, monitoring 400 individuals of Aratus pisonis and Scylla serrata showed that the pre-molting stage warning accuracy of the present application was 97.9%, the approaching molting stage accuracy was 97.1%, and the comprehensive prediction accuracy was 97.5%. The misjudgment rate decreased from 41.5% to 2.5% compared to the control group, and the multi-index collaborative verification effectively avoided the judgment errors caused by environmental fluctuations and individual differences.

[0034] III. Clear early warning level, distinguish between "pre-molt" and "molt approaching" two levels of early warning, adapt to the management needs of different stages; greatly improve the success rate of molting and significantly reduce the mortality rate. The present application constructs a pre-molt early warning and molt approaching confirmation grading early warning system, and supports targeted management measures. In the breeding test, the experiment group (n=100) using the present application has a molting success rate of 95.0%, while the control group (n=100) using traditional management has a molting success rate of only 68.0%; the hidden structure reduces the mutual cannibalism of mud crabs during the molting period, and the precise water quality control provides support for the formation of new shells, reducing the mortality rate from 32.0% to 4.0%, effectively solving the core problems of molting difficulty and high mortality rate in traditional breeding. The method of the present application for predicting the molting of mud crabs based on behavior and morphological characteristics significantly extends the early warning management window and significantly improves the initiative of breeding management. The prior art can only predict when the mud crab shows obvious abnormalities (1-2 days before molting), resulting in hasty management operations; the present application can output pre-molt early warning 12-15 days before molting by monitoring the joint diameter of the base joint of the chelae and ambulatory legs, the color change of the joint, the width of the continuous raised line of the posterior and lateral edges of the carapace of the mud crab, the length of the setae of the outer edge of the umbilicus of the mud crab, and the color of the umbilicus, etc. Compared with the traditional early warning period of 1-2 days, the effective early warning management window of the method of the present application is extended by more than 500%, providing sufficient time for the breeder to complete water quality adjustment, hidden object arrangement, and high-protein bait (protein content ≥40%) preparation, etc., improving the implementation rate of management measures, and reversing the passive situation of breeding management.

[0035] IV. Strong operability, using conventional equipment such as high-precision image measuring instruments and high-definition cameras, without the need for complex hardware investment, and easy to scale up. The method of the present application for predicting the molting of mud crabs based on behavior and morphological characteristics reduces the breeding management cost and significantly improves the comprehensive economic benefits. The present application realizes the automatic statistics of behavior parameters such as activity frequency and appendage upright frequency by continuous shooting with a high-definition camera with a frame rate of ≥30 fps combined with image analysis software, replacing the traditional manual patrol every 2 hours; at the same time, standardized instrument measurement reduces the repetitive labor of manual judgment, reducing the frequency of manual patrol to twice a day. In addition, targeted feeding under the support of accurate prediction (3 times a day during the pre-molt period, with a single feeding amount of 3%-4% of body weight) increases the feed utilization rate from 52.5% to 76.8% (an increase of 24.3 percentage points), combined with the advantage of increasing the overall molting survival rate of mud crabs from 82.0% to 98.0%, the comprehensive breeding economic benefits are significantly improved. DETAILED DESCRIPTION

[0036] The present application will be further described in detail by specific examples. The raw materials, reagents or devices used in the examples and comparative examples are commercially available or can be obtained by prior art methods unless otherwise specified. The test or test method is a conventional method in the art unless otherwise specified. The equipment used in the examples is shown in Table 1 below: Table 1 Experimental instruments and equipment

[0037] Example 1 This example provides a screening method for predicting the molting behavior and morphological characteristics of blue crabs.

[0038] This example obtains the following characteristics by screening: enhanced feeding behavior, changes in appendage joints, edge characteristics of the carapace, changes in the length and color of the umbilical setae, and changes in the abdominal morphology, which are used to determine that the blue crab has entered the “pre-molting” stage 12-15 days before molting; changes in feeding and activity patterns, softening of specific tissues, increased respiratory rate, and wiping behavior, which are used to determine that the blue crab has entered the “imminent molting” stage and is expected to molt within 1-2 days.

[0039] The principle of selecting the enhanced feeding behavior feature for predicting the molting behavior is that protein is the core raw material for building new exoskeleton and repairing body tissue during the molting process of blue crabs. The main component of the new shell is a chitin and protein complex. Before molting, blue crabs need to accumulate a large amount of protein to meet the synthesis requirements of the new shell. Otherwise, they will be unable to molt due to insufficient nutrition, resulting in a soft new shell, difficulty in molting, or an increased mortality rate after molting. Fresh bait such as small fish, shrimp, and shellfish with a protein content of ≥40% not only has a much higher protein content than organic detritus and low-protein algae, but also has an amino acid composition that is closer to the nutritional needs of blue crabs, is easily digested and absorbed, and can be quickly converted into raw materials for building new shells. At the same time, as a carnivorous crustacean, blue crabs naturally have a preference for fresh bait, and their feeding priority is higher than that of other types of bait. When providing this type of bait, blue crabs have a higher feeding enthusiasm and a more stable feeding amount, ensuring sufficient nutrient intake. If low-protein or indigestible bait is fed, even if the feeding amount increases, it will be difficult to meet the nutritional needs of molting, and instead, the low utilization rate of the bait will lead to water quality deterioration.

[0040] Meanwhile, the normal baseline level is the average daily food intake of the crab during the stable period (7-20 days after molting), and the fluctuation range of the daily food intake of the crab during the stable period is not more than ±5%. The crab will experience a growth cycle of “recovery period-stable period-molting preparation period” after molting: in the first 7 days after molting, the new shell of the crab has not yet hardened completely, and the physiological function is in a recovery state, so the food intake is low and fluctuates greatly; in the 7-20 days after molting, the new shell has hardened completely, the physiological state of the crab is stable, the growth and metabolism are smooth, the feeding behavior is not affected by the physiological changes related to molting, and the daily food intake is maintained at a relatively constant level, with a fluctuation range controlled within ±5%, thus having stability and reliability as a normal baseline.

[0041] The appendage joint change feature includes joint swelling and color change features. For the appendage joint change feature of joint swelling, an electronic caliper with an accuracy of 0.01 mm is used to measure the appendage joint diameter at the junction of the cheliped base segment and the body segment and the junction of the walking foot base segment and the body segment, 3 times for each part, and the average value is compared with the average value of the corresponding part in the normal state to calculate the swelling rate. The principle is that the hormone level in the crab changes before molting, which will promote the aggregation of blood lymph to the junction of the cheliped base segment and the body segment and the junction of the walking foot base segment and the body segment, providing nutrients and water for the development of the new shell, and at the same time causing physiological swelling of the joint at this part, and the joint diameter increases by more than 3% compared with the normal state, which is an important morphological signal before molting. Since the swelling degree is relatively subtle, ordinary measuring tools are difficult to accurately capture, and the swelling conditions of different joint parts are different, and only measuring a single part may cause data deviation due to individual posture or accidental factors. The electronic caliper with an accuracy of 0.01 mm can accurately measure the subtle diameter change, ensuring the accuracy of the data; and the key joint parts of the cheliped and walking foot are selected for measurement, which can comprehensively reflect the overall swelling state of the crab appendage joint; measuring 3 times for each part and taking the average value can effectively reduce the random error in the measurement process, making the calculation of the swelling rate more objective. If the measuring tool accuracy is insufficient, the measurement part is not clear, or the measurement times are too few, the swelling rate calculation will be biased, and the crab cannot be accurately judged whether it has entered the pre-molting period. The swelling degree judgment in the appendage joint change feature provides a standardized and high-precision measurement scheme, which converts joint swelling into quantitative swelling rate data, avoids the error of subjective visual judgment, ensures the consistency and reliability of the feature judgment, and provides a solid quantitative basis for pre-molting identification.

[0042] For the color change of the appendage joint, the colorimetric value was measured by using the standard color card (GB / T 22290-2008). The measurement was carried out under natural light conditions (light intensity 5000-10000 lx), and the measurement area was the swollen part of the appendage joint and the adjacent normal skin area. Each area was measured 3 times to take the average value. The principle is that during the pre-molting stage, the blood lymph of the crab's appendage joint accumulates and the epidermis ages, and the epidermal cells gradually fall off, resulting in a lighter color of the joint epidermis, which appears white or milky white, and the colorimetric value is reduced by more than 10% compared with the normal area. This color change is an important signal for the separation of the epidermis and the old shell. However, color judgment is easily affected by light conditions and observer's subjective visual differences. The color of the same part under different light intensities may show significant differences, and it is difficult to accurately quantify the degree of color change by naked eye observation. The use of standard color cards in line with national standards (GB / T 22290-2008) can provide a unified color reference scale and ensure the standardization of colorimetric value judgment. The measurement under the condition of natural light with a light intensity of 5000-10000 lx can avoid the interference of strong light, weak light or artificial light source on color observation, and ensure the consistency of the measurement environment. At the same time, the measurement of the joint swelling part and the adjacent normal skin area can exclude the influence of the color difference of the individual crab itself, and accurately capture the unique color change during the pre-molting stage. Measuring each area 3 times to take the average value can reduce accidental errors and improve data reliability. The role is to convert the subjective judgment index of the color change of the appendage joint into objective and quantifiable colorimetric value data, eliminate the judgment deviation caused by light and human factors, and ensure the accuracy and repeatability of the appendage joint change characteristics, providing a scientific and unified judgment standard for pre-molting identification.

[0043] For the edge features of the cephalothorax, a digital vernier caliper with an accuracy of 0.01 mm was used to measure the width of the continuous raised lines formed on the posterior and lateral edges of the cephalothorax of the mud crab. Measurements were taken at three locations: the midpoint of the posterior edge of the cephalothorax and the midpoints of the left and right lateral edges. Each measurement was taken three times perpendicular to the line's direction, and the arithmetic mean was used as the final width value. The principle is that during the early molting stage of the mud crab, the new shell begins to develop and separate from the old shell. As the main protective structure of the body, the growth of the new shell inside the old shell causes obvious raised lines to appear on the posterior and lateral edges of the cephalothorax. The width of these lines directly reflects the degree of development of the new shell. When the width is ≥0.5 mm, it indicates that the new shell has reached a certain thickness, and the mud crab has entered the early molting stage. Because the raised lines on the edge of the cephalothorax may have local variations in thickness, measuring only a single location would result in unrepresentative data. Therefore, measurements were taken at three locations: the midpoint of the posterior edge of the cephalothorax and the midpoints of the left and right lateral edges. Since the line width is 0.5 mm or more, high-precision measuring tools are required for accurate measurement. Using a digital vernier caliper with an accuracy of 0.01mm, the system can meet the measurement needs for minute widths, ensuring data accuracy. Measurements are taken at three points: the midpoint of the posterior edge of the cephalothorax and the midpoints of the left and right lateral edges. This comprehensively reflects the overall width of the lines, avoiding misjudgments caused by local differences. Each measurement is taken three times perpendicular to the line's direction, and the arithmetic mean is calculated. This reduces measurement angle deviations and random errors, ensuring the objectivity and accuracy of the results. Random measurement positions, insufficient tool precision, or too few measurements can lead to inaccurate judgments of the raised line width, making it impossible to accurately identify pre-molting stages. This system provides a standardized, high-precision measurement method for cephalothorax edge features, using a raised line width ≥0.5mm as a quantitative indicator to avoid the ambiguity of subjective observation, ensuring the accuracy of this feature's judgment and providing crucial morphological evidence for pre-molting stage identification.

[0044] The length of the abdominal setae was measured using a high-precision image measuring instrument. The specific procedure involved fixing the mud crab sample on a stage, acquiring high-resolution images of the setae region around the outer edge of the abdominal setae, converting the pixel count to the actual length using a standard calibration ruler, and measuring the length along the main axis of the setae. The measurement accuracy was ±0.1 mm. The principle behind this is that the growth of the abdominal setae in mud crabs is closely related to their physiological cycle. During the pre-molting period, changes in hormone levels in the mud crab stimulate rapid growth of the abdominal setae, increasing by 20% or more compared to the non-molting period. This is an important physiological signal during the pre-molting period. However, the abdominal setae are thin and short, and the mud crabs may struggle during measurement. Directly using calipers or other tools can easily lead to setae breakage and measurement angle deviations, making it difficult to obtain accurate data. High-precision image measuring instruments perform non-contact measurements by acquiring high-definition images, avoiding damage to the bristles from direct measurement while clearly presenting the complete shape of the bristles. A standard calibration ruler accurately converts pixels to actual length, translating pixel distances in the image into actual physical lengths, ensuring measurement accuracy. Measurement along the bristle's main axis avoids length errors caused by measurement path deviation, achieving a measurement accuracy of ±0.1mm, sufficient to capture length increases of 20% or more. Improper measurement methods or insufficient tool precision can lead to distorted bristle length measurement data, making it impossible to accurately determine whether the characteristics of the pre-molting stage are met.

[0045] The method for measuring the color of the abdominal navel involves acquiring images of the navel area under a standard light source and extracting L and b values ​​using the CIE Lab color space. When L ≥ 80 and b value is within the range of 10-20, it is considered pure white. When the b value rises to the range of 20-30, it is considered a gradual change towards pale yellow. The principle behind this is that the color change of the mud crab's abdominal navel is closely related to its internal physiological state: during the non-molting period, the epidermal cells of the abdominal navel are metabolically stable and appear pure white; after entering the pre-molting stage, changes occur in the mud crab's water metabolism and pigment deposition, and the epidermis of the abdominal navel gradually changes towards pale yellow. This color change is an important signal of the pre-molting stage. However, subjective judgment of color is easily affected by differences in light source and observer's vision, making it difficult to establish a unified standard. The CIE Lab color space is an internationally recognized color quantification system. The L value represents brightness, and the b value represents the yellow-blue axis (the larger the b value, the more pronounced the yellow tint). This color space allows the color of the navel to be converted into objective numerical parameters. Acquiring images under standard light sources avoids interference from natural light intensity and color temperature variations, ensuring a consistent measurement environment. By setting clear L and b value ranges, "pure white" and "gradual transition to pale yellow" are quantified, transforming color judgment from subjective visual perception to objective data comparison. Without standardized measurement methods and quantification standards, judging navel color changes solely through visual observation is prone to bias, affecting the accuracy of early molting identification.

[0046] The abdominal morphological changes in mud crabs are characterized by a slight overall bulge in the abdomen. The vertical distance between the central part of the abdominal carapace and the posterior edge of the cephalothorax is increased compared to non-molting individuals with similar body width. Measurements were taken using a digital height gauge with an accuracy of 0.01 mm. During measurement, the mud crab was placed on a horizontal experimental table with its abdominal carapace facing down and allowed to rest naturally. The vertical distance between the highest point of the central part of the abdominal carapace and the lowest point of the posterior edge of the cephalothorax was measured. The principle is that in the pre-molting stage, mud crabs actively absorb water and accumulate it in the abdomen to provide space for the development of the new shell. Simultaneously, the growth of the new shell on the inner side of the abdomen causes an overall bulge, significantly increasing the vertical distance between the central part of the abdominal carapace and the posterior edge of the cephalothorax—by 5% or more compared to non-molting individuals with similar body width. This distance change directly quantifies the abdominal bulge characteristic. During the measurement process, the placement posture of the mud crab and the selection of the measurement reference point directly affect the measurement results: if the mud crab is not allowed to rest naturally, the abdomen may be in a contracted or twisted state due to struggling, leading to inaccurate distance measurements; if the measurement reference point is unclear, measurement position deviations will occur. Placing the mud crab on a horizontal experimental platform with its plastron facing down and allowing it to stand naturally ensures that the measurement reference plane is level and that the abdomen is in a natural state. Using a digital height gauge with an accuracy of 0.01 mm can accurately capture distance changes of up to 5%. Clearly measuring the vertical distance between the highest point in the center of the plastron and the lowest point at the posterior edge of the cephalothorax can avoid errors caused by fuzzy measurement points and ensure the consistency of measurement results.

[0047] The softening characteristics of specific tissues include a decrease in hardness of more than 20% in the abdominal carapace area below the longest serrations on both sides of the cephalothorax of the mud crab compared to non-molting individuals. This was measured using a Shore A hardness tester. The instrument was calibrated before measurement. During measurement, the probe was perpendicular to the abdominal carapace surface, and a pressure of 1 N was applied. Each measurement site was measured three times, and the average value was compared with the average hardness of the same site in non-molting individuals to calculate the rate of hardness reduction. The principle is that, near molting, the mud crab secretes molting hormones, which stimulate the epidermal cells on the inner side of the old shell to secrete enzymes that break down the proteins and calcium carbonate in the old shell, gradually softening and thinning it to facilitate molting. The specific area of ​​the abdominal carapace (below the longest serrations on both sides of the cephalothorax) is the main breakthrough point during molting, showing the most significant softening of the old shell, with a hardness decrease of more than 20% compared to non-molting individuals. This is a core morphological signal indicating the approaching molting stage. The accuracy of hardness measurement is affected by factors such as instrument calibration, measurement pressure, and probe angle. If the instrument is not calibrated, the measurement reference will be deviated; if the probe is not perpendicular or the applied pressure is unstable, the measurement data will fluctuate significantly. Calibrating the instrument before measurement ensures the accuracy of the hardness tester; applying a pressure of 1N perpendicular to the plastron surface ensures consistent measurement conditions and avoids distortion of hardness data due to differences in pressure or angle; taking three measurements for each part and averaging them reduces random errors and improves data reliability; comparing the hardness of the same part with that of individuals not in the molting period to calculate the rate of decrease can eliminate the hardness differences within the individual crab and accurately reflect the degree of softening of the old shell.

[0048] Activity pattern changes; increased respiratory rate and wiping behavior were recorded continuously using a high-definition camera (frame rate ≥30fps) for at least 1 hour, and relevant behavioral parameters were statistically analyzed using image analysis software. Respiratory rate was determined by manually counting the number of times the gill covers opened and closed, with each count lasting 1 minute, repeated 3 times at 5-minute intervals, and the average value was taken. One to two days before molting, the mud crab undergoes a dramatic physiological change. It first accumulates energy by lying still, then, due to the loosening of the old shell and the imminent emergence of the new shell, its activity rate increases significantly, and its appendages stand upright to find support for molting. Certain areas of the abdominal carapace experience a decrease in hardness due to the redissolution of calcium carbonate from the old shell, leading to an increased respiratory rate to meet the demands of high metabolism. Simultaneously, wiping behavior cleans the body surface of attached substances and loosens the seams of the old shell, making final preparations for molting.

[0049] Meanwhile, in this embodiment, healthy mud crabs (non-molting mud crabs) with a body width difference of ≤5% and a weight difference of ≤10% compared to the tested mud crabs, and which are in a stable period of 7-15 days after molting, were selected as the benchmark for measuring the characteristics of appendage joint changes, carapace edge characteristics, abdominal umbilical setae length and color changes, abdominal morphological changes, tissue softening characteristics in specific areas, increased respiratory rate, and wiping behavior. The principle is that the morphological parameters (such as appendage joint diameter and vertical distance between the abdominal carapace and carapace) and physiological parameters (such as abdominal carapace hardness and respiratory rate) of mud crabs are significantly affected by body width, weight, and growth stage: mud crabs with large differences in body width and weight have significant differences in their basic morphology and physiological indicators, and using them as a reference will lead to distorted comparison results; mud crabs within 7 days after molting have not fully hardened their new shells, their physiological state is unstable, and various parameters fluctuate greatly, making them unworthy of reference; and mud crabs in poor health may have abnormal morphological and physiological parameters due to disease, which cannot reflect the normal non-molting state.

[0050] Selecting individuals with a body width difference of ≤5% and a weight difference of ≤10% from the crab to be tested ensures that the reference crabs are similar in size to the crabs to be tested, eliminating the interference of body size differences on parameter comparison; limiting them to the stabilization period of 7-15 days after molting ensures that the physiological state of the reference crabs is stable and that all parameters are at normal levels; requiring healthy crabs avoids reference bias caused by disease factors.

[0051] This embodiment provides standardized quantitative measurement methods for characteristics such as enhanced feeding behavior, changes in appendage joints, cephalothorax edge features, changes in the length and color of the umbilicus setae, changes in abdominal morphology, changes in activity patterns, softening of tissues in specific areas, increased respiratory rate, and wiping behavior. This provides an objective and operable measurement basis for predicting molting in mud crabs and ensures the accuracy of the characteristic judgment.

[0052] Example 2 This embodiment provides a method for predicting the molting of mud crabs based on behavioral and morphological characteristics. The mud crabs in the non-molting period are healthy mud crabs with a body width difference of ≤5% and a weight difference of ≤10% compared to the mud crabs to be tested, and which are in a stable period of 7-15 days after molting. The culture water is filtered seawater with a salinity of 12-18%, aerated for 24 hours in advance, with the temperature stable at 24-26℃, the pH value of the water body of 7.8-8.2, and the dissolved oxygen content of ≥5.0mg / L, as detailed below.

[0053] The feeding behavior of mud crabs was recorded at fixed times every day (8:00, 14:00, 22:00), and the daily feed intake and preference for high-protein live bait were statistically analyzed.

[0054] The following five quantitative characteristics were measured daily using standardized instruments and monitored continuously for 15 days. The judgment criteria and duration of each characteristic were recorded. When the mud crab meets at least three of the five characteristics (1)-(5) and lasts for ≥3 days, it is marked as entering the pre-molting stage, which is 12-15 days away from molting.

[0055] (1) Enhanced feeding behavior Operating procedures: Feed a fixed amount of feed daily (initial feed amount is 5% of the body weight of the mud crab). After 2 hours, collect the remaining feed, dry it to constant weight, and calculate the actual feed intake. Record the feed intake for 7 consecutive days during the stabilization period, and take the average value as the normal baseline level. During the experiment, record the mud crab's feeding preference for high-protein live feed (fish (sardines), shrimp (Litopenaeus vannamei), and shellfish (razor clams) with protein content ≥40%, after being chopped and fed) and low-protein feed (corn, soybean meal). The normal baseline level is the average daily feed intake of mud crabs during the stabilization period after molting (7-20 days after molting), during which the daily feed intake of mud crabs fluctuates by no more than ±5%.

[0056] Daily food intake improvement rate = (daily food intake during the testing period - normal baseline level) / normal baseline level × 100%; The normal baseline level is the average daily feed intake of mud crabs during the stable period after molting (7-20 days after molting), during which the daily feed intake of mud crabs fluctuates by no more than ±5%.

[0057] Judgment criteria: If the daily food intake of mud crabs is 20% or more higher than the normal baseline level, and the feed is relatively low in protein, and the mud crabs preferentially consume high-protein fresh feed, then this characteristic criterion is met. (2) Characteristics of changes in appendiceal joints Operating steps: Use electronic calipers to measure the diameter at the junction of the coxae and somites of the chelipeds and the junction of the coxae and somites of the walking legs. Measure each location three times and take the average value. Use a standard colorimetric card under natural light conditions (light intensity 5000-10000 lx) to measure the color values ​​of the joint areas (junction of the coxae and somites of the chelipeds and the junction of the coxae and somites of the walking legs) and adjacent normal skin areas. Measure each area three times and take the average value. Compare the average value with the corresponding average value of the area under non-molting conditions to calculate the swelling rate.

[0058] Joint swelling rate = (joint diameter during the detection period - joint diameter before molting) / joint diameter in normal condition × 100%; Chromaticity value decrease rate = (Chromaticity value of adjacent normal area at joint site - Chromaticity value of joint site) / Chromaticity value of adjacent normal area × 100%; Judgment criteria: The base joints of the claws and walking legs of the mud crab show swelling due to hemolymph accumulation, with the joint diameter increasing by 3% or more compared to the normal state (joint swelling rate). At the same time, the skin at the joint becomes lighter in color, appearing whitish or milky white. Based on standard colorimetric card measurements, its color value is reduced by 10% or more compared to the normal area to meet the characteristics.

[0059] (3) Features of the cephalothorax margin Operating steps: Use a digital vernier caliper to measure the width of the raised lines at three points: the midpoint of the posterior edge of the cephalothorax and the midpoint of the left and right lateral edges. Measure each point three times perpendicular to the direction of the line and take the arithmetic mean.

[0060] Judgment criteria: The width of the raised line is ≥0.5mm to meet the feature.

[0061] (4) Characteristics of changes in the length of the umbilicus bristles and the color of the umbilicus Operating steps: Acquire high-resolution images of the bristles on the outer edge of the umbilicus using a high-precision image measuring instrument. Convert pixels to actual length using a standard calibration ruler and measure the length along the bristle's main axis. Acquire images of the umbilicus under a standard light source. Extract L-values ​​(brightness, ranging from 0 to 100, where 0 represents pure black and 100 represents pure white) and b-values ​​(ranging from yellow to blue, ranging from -128 to 127, where positive values ​​indicate a yellowish tint and negative values ​​indicate a bluish tint) using the CIELab color space. When the L-value is ≥80 and the b-value is in the range of 10-20, it is considered pure white. When the b-value rises to the range of 20-30, it is considered a gradual transition to pale yellow. A standard light source box is used to obtain the standard light source.

[0062] The growth rate of setae length = (setae length of mud crabs during the detection period - setae length of mud crabs outside the molting period) / setae length of mud crabs outside the molting period × 100%; Judgment criteria: The bristle length growth rate is ≥20%, and the color of the navel changes from pure white to light yellow, that is, the b value reaches 20-30 (light yellow gradient) to meet the characteristics.

[0063] (5) Characteristics of abdominal morphological changes Operating procedures: Place the mud crab on a horizontal experimental table with its plastron facing down and let it stand naturally. Use a digital height gauge to measure the vertical distance between the highest point in the center of the plastron and the lowest point at the posterior edge of the cephalothorax. Select mud crabs of similar body width that are not in their molting stage as a reference.

[0064] Vertical distance increase rate = (vertical distance during detection period - vertical distance during non-molting period) / vertical distance during non-molting period × 100%; Judgment criterion: an increase rate of 5% or more is considered to meet the feature.

[0065] 4. The fourth day after the mud crab meets the characteristics of the pre-molting stage is recorded as the first day of the pre-molting stage. When the 10th day of the pre-molting stage begins, the behavior, hardness of the abdominal carapace and respiratory rate of the mud crab are continuously monitored. The monitoring is carried out 4 times a day (8:00, 12:00, 16:00 and 22:00). The behavior of the mud crab is continuously filmed with a high-definition camera for no less than 1 hour each time. The activity frequency, number of times the appendages stand upright and the number of times the wiping action are counted by image analysis software. When the mud crab meets all 4 characteristics of (1)-(4) below, it is determined that it has entered the "imminent molting period" stage and is expected to molt within 1-2 days. The activity frequency, number of times the appendages stand upright and the number of times the wiping action are counted by continuous filming with a high-definition camera (frame rate ≥30 fps) for no less than 1 hour. The relevant behavioral parameters are counted by image analysis software. The respiratory rate is counted by manually counting the number of times the gill cover opens and closes. Each count lasts for 1 minute and is repeated 3 times with a 5-minute interval. The average value is taken.

[0066] (1) Characteristics of activity pattern change: The high-definition camera was used to continuously record for 1 hour, and the resting time, number of movements per unit time and number of times the appendages were upright were statistically analyzed using image analysis software.

[0067] Activity frequency increase rate = (Number of moves during the detection period - Number of moves during the resting period) / Number of moves during the resting period × 100%; The resting period is 2-4 days before the mud crab molts. During this time, the mud crab reduces or stops feeding, does not move, and rests quietly in a secluded corner. The resting period usually lasts 1-2 days. The number of times the mud crab moves during this period is used as the number of times it moves during the resting period.

[0068] Judgment criteria: After resting for 24-48 hours, if the activity frequency increases by 300% or more, and the appendages are upright ≥5 times per hour and each time lasts ≥15 seconds, showing that the walking legs or chelipeds support the body vertically and the head and thorax are raised off the ground, then the characteristics are met.

[0069] (2) Tissue softening characteristics of specific parts: The hardness of the abdominal carapace below the longest serration on both sides of the cephalothorax of the mud crab was measured. The hardness of the abdominal carapace was measured using a Shore hardness tester (Type A). The instrument was calibrated before measurement. During measurement, the probe was perpendicular to the surface of the abdominal carapace and a pressure of 1N was applied. Each measurement site was measured 3 times, and the measurement was performed 3 times a day. The average value was compared with the average hardness of the same part of the individual in the non-molting period to calculate the hardness reduction rate.

[0070] Hardness reduction rate = (Penal plate hardness during non-molting period - Penal plate hardness during testing period) / Penal plate hardness during non-molting period × 100%; Judgment criteria: The characteristic is met when the rate of decrease in hardness is 20% or more lower than that of individuals in the non-molting period.

[0071] (3) Increased respiratory rate: Manually count the number of times the gill cover opens and closes, each count lasts for 1 minute, repeat 3 times with a 5-minute interval, and take the average value to calculate the respiratory rate.

[0072] Judgment criteria: A respiratory rate of 13-16 breaths / minute, which is 30% or more higher than the normal level, is considered to meet the criteria.

[0073] (4) Wiping behavior characteristics: The camera continuously recorded for 1 hour, and the number of times the chelicerae scraped the joint between the plastron and carapace and the duration of each action were counted by image analysis software. The total daily cleaning behavior time was accumulated.

[0074] Judgment criteria: ≥20 actions per hour, each action lasting ≥10 seconds, and a total daily cleaning time of ≥5 minutes are required to meet the criteria.

[0075] Example 3 This embodiment provides experimental verification of pre-molting identification in mud crabs. It verifies the accuracy of identification using five quantitative characteristics from Example 2 (enhanced feeding behavior, changes in appendage joints, cephalothorax edge characteristics, changes in abdominal setae and color, and changes in abdominal morphology) during the pre-molting period (12-15 days before molting) in mud crabs. The results are compared with the control group using relevant literature (Hou Yiling, Cheng Wenzhi, Wei Yiming, et al. Research progress on the identification technology of molting cycle stages in shrimp and crabs [J]. Fisheries Science). ,2024,43(02):319-332.DOI:10.16378 / j.cnki.1003-1111.22058;Xuan Fujun, Jiang Senhao, Bian Xunguang, et al. Reproductive molting and mating behavior of blue crab under indoor culture conditions[J]. Zoological Journal,2014,49(04):579-586.DOI:10.13859 / j.cjz.201404015.;Kennedy, VS,&Cronin, LE (2007).The blue crab: Callinectes sapidus.) Comparison of indicators.

[0076] In this embodiment, the experimental bait was divided into two categories: high-protein live bait, which consisted of small fish (sardines), shrimp (whiteleg shrimp), and shellfish (razor clams) with a protein content of ≥40%, was chopped and mixed with low-protein plant bait (corn, soybean cake, etc.) in a fixed ratio (1:1) and fed to the crabs. The crabs' preference for high-protein live bait and low-protein plant bait was evaluated by observing their feeding behavior and selection preferences for the two types of ingredients in the mixed bait.

[0077] The aquaculture water is filtered seawater with a salinity of 12-18%, pre-aerated for 24 hours, and the temperature is stabilized at 24-26℃ with a dissolved oxygen content ≥5.0mg / L. The recirculating aquaculture tanks are single tanks with dimensions of 60cm×40cm×30cm, equipped with simple hiding places, and use a recirculating aquaculture system (RAS), model AquacareSystemsRAS-2000.

[0078] The specific experimental steps are as follows: Select the mud crab that is used for burrowing ( Scylla paramamosain ), Sawtooth Blue Crab ( Scylla serrata Two hundred healthy individuals from each species were selected, with a body width of 3-5 cm and a weight of 20-30 g, and were in the stable period (non-molting period) 7-15 days after molting. The two species of mud crabs were randomly divided into an experimental group and a control group, with 100 crabs in each group, and were raised separately in breeding tanks of the same size.

[0079] Experimental group: The five quantitative characteristics specified in Example 2 for the early molting stage were used as detection indicators to determine whether the mud crab had entered the early molting warning stage.

[0080] Control group: Early molting characteristics obtained from the above-mentioned relevant literature were used as detection indicators, including body surface color, color of the swimming foot joints, presence or absence of molting sutures, and degree of curvature of the xiphoid process.

[0081] The specific operating procedure is as follows.

[0082] Experimental group operating procedures: The feeding behavior of mud crabs was recorded at fixed times every day (8:00, 14:00, 22:00), and the daily feed intake and preference for high-protein live bait were statistically analyzed.

[0083] Five quantitative characteristics of the pre-molting stage in Example 2 were measured daily using standardized instruments for 15 consecutive days. The accuracy and duration of each characteristic were recorded. When the mud crab met at least three of the five characteristics for at least three consecutive days, it was marked as a predicted entry into the pre-molting stage. The actual molting time was tracked and recorded to verify the accuracy of the prediction.

[0084] Control group procedure: At fixed times each day (8:00 AM and 4:00 PM), the following indicators were recorded using corresponding instruments: whether the skin color lightened, whether black marks appeared on the soles of the feet during swimming, whether peeling sutures appeared, and whether the xiphoid process showed slight curvature. Details are as follows: Changes in body surface color were measured using standard colorimetric cards, just like in the experimental group.

[0085] The pigment deposition in the soles of swimmers' feet was detected using dermoscopy. The specific procedure was as follows: high-resolution imaging of the swimmer's footprint area was performed using a dermoscope, followed by image analysis software to process and quantitatively evaluate the acquired images, focusing on the structural characteristics such as the uniformity of epidermal pigment deposition distribution and deposition depth.

[0086] The observation of molting sutures was performed using a magnifying glass. The specific procedure was as follows: the crab was fixed in a dissecting tray and a magnifying glass (10× magnification) was used to systematically examine the dorsal region of the cephalothorax. The focus was on whether there were any tiny cracks or weak areas in the shell caused by water absorption at the junction of the carapace and the plastron (i.e., the posterior edge of the plastron).

[0087] The degree of curvature of the scimitar was detected using image analysis. By taking a photo of the scimitar, the curvature parameters were measured using image processing software (such as ImageJ). Specifically, the crab's head was placed flat, and a clear side view of the scimitar was taken with a mobile phone or camera. The photo was imported into ImageJ software, and the contrast was adjusted to make the outline of the scimitar clear. The line segment tool in ImageJ software was used to measure the chord length (L) and arc height (h); the angle tool in ImageJ software was used to measure the curvature angle (θ). The measurement was repeated 3 times, and the average value was taken.

[0088] When ≥3 traditional characteristics change, it is marked as a predicted entry into the pre-molting stage. The actual molting time is tracked and recorded to verify the accuracy of the prediction.

[0089] The characteristics of appendage joint changes, carapace edge features, abdominal umbilical setae length and color changes, and abdominal morphological changes in the experimental group were all based on the characteristics detected in non-molting mud crabs, as well as those in the control group.

[0090] The experimental results are shown in Tables 2-4 below. Tables 2 and 3 show that the experimental group achieved a 97.9% accuracy rate in identifying the pre-molting stage with a false positive rate of only 2.1%, significantly better than the control group's 65.9% accuracy rate and 34.1% false positive rate. This indicates that the five quantitative features for predicting the molting stage of mud crabs can accurately capture the physiological changes during this period. Table 4 shows that the average satisfaction rate of each feature in the experimental group among correctly identified individuals was between 93.6% and 100%. Among them, the satisfaction rate of the appendage joint changes and the cephalothorax edge features both reached 100%, indicating that these two features are the core signals for the pre-molting stage and have strong stability. The traditional indicators in the control group were greatly affected by subjective observation. For example, there were individual differences in judging the body surface color and the color of the swimming foot segments. Furthermore, features such as the molting suture and the curvature of the rostrum appeared later, resulting in a lower accuracy rate and failing to effectively achieve pre-molting warning.

[0091] There was no significant difference in the identification accuracy between the two types of mud crabs in the experimental group, indicating that the method of the present invention is applicable to the identification of different species of mud crabs in the pre-molting stage and has strong versatility. The number of correctly identified individuals in the experimental group was 94 for *Scylla serrata* and 93 for *Scylla serrulata*, providing a sufficient and qualified source of experimental subjects for subsequent studies.

[0092] Table 2. Pre-molting identification data of the experimental group

[0093] Table 3. Identification data of the control group in the early molting stage

[0094] Table 4. Statistics on the Satisfaction of Various Characteristics in the Experimental Group

[0095] Example 4 This embodiment provides experimental verification of the identification of the molting period, verifying the accuracy of the four quantitative characteristics of the molting period in Example 2 (activity pattern change characteristics, tissue softening characteristics in specific areas, increased respiratory rate characteristics, and wiping behavior characteristics) for the identification of the molting period (within 1-2 days) of mud crabs. The specific experimental steps are as follows, by comparing with the relevant literature indicators of the control group.

[0096] The experimental breeding conditions and feed used in this embodiment are the same as in embodiment 3, and the ceramic pipes and tiles are placed in the corners of the recirculating aquaculture tank.

[0097] In Example 3, mud crabs that were correctly predicted to be in the pre-molting stage were selected. After molting, they were again predicted to be in the pre-molting stage and used in this example. Seventy mud crabs (Scylla serrata) and seventy mud crabs (Scylla serratedis) were selected, all healthy individuals, with a body width of 5-7 cm and a weight of 40-60 g, clearly indicating they had entered the pre-molting stage (12-15 days before molting). Seventy mud crabs were randomly selected from each of the correctly predicted individuals to form experimental and control groups: 35 mud crabs in the experimental group and 35 in the control group; and 35 mud crabs in the experimental group and 35 in the control group. These were raised separately in identical tanks.

[0098] Experimental group: Four quantitative characteristics of the molting stage in Example 2 were used as detection indicators to determine whether the mud crabs had entered the molting stage. Each group consisted of 35 crabs.

[0099] Control group: The characteristics of imminent molting obtained from relevant literature in Example 3 were used as detection indicators, including reduced or stopped food intake, reduced or stopped activity, reduced aggression, and overall decrease in shell hardness. There were 35 animals in each group.

[0100] The specific experimental steps are as follows: Specific operating procedures for the experimental group: Starting on the 10th day of the pre-molting phase, the behavior, carapace hardness, and respiratory rate of the mud crabs were continuously monitored four times daily (8:00, 12:00, 16:00, and 22:00). High-definition cameras were used to continuously film the crabs' behavior for at least one hour each time. Image analysis software was used to statistically analyze activity frequency, number of times appendages were erected, and number of wiping movements. The hardness of the plastron region below the longest serrations on both sides of the cephalothorax was measured using a Shore A hardness tester, with three measurements taken daily and the average value recorded. The number of times the gill covers opened and closed was manually counted, with each count lasting one minute, repeated three times at 5-minute intervals, and the average value was used to calculate the respiratory rate.

[0101] When a mud crab simultaneously meets all four characteristics of the molting period in Example 2, it is marked as molting within 1-2 days. The actual molting time is tracked and recorded to verify the accuracy of the prediction.

[0102] Specific operating procedures for the control group: Starting on the 10th day of the pre-molting phase, the traditional pre-molting characteristics of mud crabs were monitored four times daily (8:00, 12:00, 16:00, and 22:00). Changes in food intake were observed and recorded. Record daily food intake; a reduction of ≥50% from normal levels or cessation of food intake is considered a satisfactory characteristic. Activity level: Observe the movement frequency of mud crabs. A decrease of ≥80% or cessation of activity compared to normal levels within 1-2 days is considered a satisfactory characteristic. Aggression: The crab is deemed to have a positive characteristic if it does not retaliate when its claws are gently touched with a small glass rod. Carapace hardness: Pressing the central area of ​​the carapace with your finger, it should feel noticeably softer, indicating that the test is satisfactory.

[0103] When a mud crab simultaneously meets all ≥4 characteristics of the control group, it is marked as being in the molting period, and molting is predicted to occur within 1-2 days. The actual molting time is tracked and recorded to verify the accuracy of the prediction.

[0104] The baseline for the softening characteristics of specific tissues in the experimental group and the characteristics of the control group were both based on the characteristics measured by non-molting mud crabs.

[0105] The experimental results are shown in Tables 5-7 below. Tables 5 and 6 show that the experimental group achieved an accuracy rate of 97.1% in identifying the molting period, with a misjudgment rate of only 2.9%, which is significantly higher than the control group's accuracy rate of 70.9% and misjudgment rate of 29.1%. This indicates that the four quantitative features of the present invention can accurately capture the behavioral and physiological signals of mud crabs nearing molting. Table 7 shows that the average satisfaction rate of various features in actual molting individuals in the experimental group was between 91.2% and 97.1%. Among them, the activity pattern change feature and the increased respiratory rate had the highest satisfaction rate (both 97.1%), which are key indicators for judging the molting period, with clear signals that are not easily interfered with. The traditional indicators in the control group are mostly qualitative descriptions, such as obvious softening of the shell and reduced activity, which are subjective. Moreover, some features (such as cessation of activity) may be caused by non-molting factors such as environmental stress, leading to a higher misjudgment rate.

[0106] The difference in identification accuracy between the two types of mud crabs in the experimental group was minimal, further verifying the versatility of the method of the present invention, applicable to accurate prediction of the molting period of different mud crab varieties. The experimental subjects were all from the correctly identified individuals in Example 3, ensuring the consistency and effectiveness of the experimental samples and avoiding interference from differences in the basic state of the samples, thus making the verification conclusions more reliable.

[0107] Table 5. Identification data of the experimental group near molting stage

[0108] Table 6. Identification data of the control group near molting period

[0109] Table 7. Statistics on the Satisfaction of Various Characteristics in the Experimental Group

[0110] Example 5 This embodiment provides an accuracy verification of the molting prediction method for mud crabs. It verifies the prediction accuracy of the prediction method in Example 3 in two stages: the pre-molting stage (12-15 days before molting) and the near-molting stage (1-2 days) in Example 4. It compares the misjudgment rate of the feature judgment method in relevant literature in Example 3. The breeding environment and feed are the same as in Example 3. The specific experimental steps are as follows.

[0111] Select the mud crab that is used for burrowing ( Scylla paramamosain ) and serrated blue crab ( Scylla serrata 200 individuals were selected from each group, with a body width ranging from 8 to 10 cm and a weight ranging from 150 to 200 g. The difference in body width was ≤5% and the difference in weight was ≤10%. All individuals were healthy and in a stable period of 7 to 20 days after molting. The experimental period was 60 days, covering the complete molting cycle of mud crabs.

[0112] Experimental group: The multi-index fusion prediction method based on behavioral and morphological features, as described in Example 2 of this invention, was used to identify and predict the molting stage of mud crabs. The specific operation is as follows: On day 1 of the experiment, 200 mud crabs were numbered, and basic data (appendage joint diameter, carapace hardness, etc.) were measured as reference values ​​for normal condition. High-definition cameras were used to continuously record images for one hour each day at 9:00, 15:00, and 21:00. Image analysis software was used to statistically analyze activity frequency, number of times appendages were erected, and number of wiping movements. Respiratory frequency was manually counted for one minute each time, repeated three times with a 5-minute interval, and the average value was taken. Every three days, appendage joint diameter and color value, width of the cephalothorax edge protrusion, and vertical distance between the plastron and cephalothorax were measured, and feeding information (daily food intake, food preference) was recorded. When a mud crab met at least three of the five pre-molting characteristics for ≥3 days, it was considered to be in the pre-molting stage; when it met all four characteristics of impending molting, it was considered to be in the impending molting stage. The warning time and actual molting time were recorded.

[0113] Control group: Combining the determination methods of the control group in Examples 3 and 4, technicians with more than 5 years of breeding experience made molting predictions based on traditional experience (relying on subjective observations such as body surface color and activity level), and recorded the predicted molting time.

[0114] The experimental results are shown in Table 8 below. The experimental group achieved a comprehensive prediction accuracy of 97.5%, with a pre-molting early warning accuracy of 97.0% and a near-molting confirmation accuracy of 98.0%, and a misjudgment rate of only 2.5%. In contrast, the control group achieved a comprehensive accuracy of only 58.5% and a misjudgment rate of 41.5%. This demonstrates that the present invention, through multi-indicator quantitative fusion judgment, effectively avoids the influence of environmental fluctuations and individual differences, improving prediction accuracy by 66.7% (an absolute improvement of 39.0%) compared to traditional methods. It can accurately pinpoint the key time nodes for molting in mud crabs, providing a reliable basis for subsequent management.

[0115] Table 8. Experimental data verifying the accuracy of the molting prediction method for mud crabs.

[0116] Example 6 This embodiment verifies the effectiveness of management measures following an early warning system for molting, specifically examining the impact of water quality regulation, feed optimization, and the deployment of concealed structures on the molting success rate and new shell development quality of mud crabs after such an early warning. The specific experimental steps are as follows.

[0117] Two hundred mud crabs of the same size as in Example 3 were selected and determined to be in the early molting stage (12-15 days before molting) by the method in Example 2 of this invention. The experimental period was 15 days, from the early molting warning to the completion of molting.

[0118] Experimental group: The aquaculture management was carried out using the supporting control measures following the early warning of the molting stage of this invention, as detailed below: (1) The water body has a stable pH value of 7.8-8.2, a temperature of 24-26℃, and a salinity of 12-18%.

[0119] (2) Install concealed structures such as ceramic pipes, tiles and wire mesh cages to achieve an environmental shading rate of 60-70%.

[0120] (3) Gradually increase the calcium ion concentration in the water to 400-500 mg / kg and maintain dissolved oxygen at 5.5-6.0 mg / L.

[0121] (4) Feed 3 times a day, with each feeding amount being 3-4% of the crab's body weight, using high-protein fresh bait.

[0122] (5) Maintain a light intensity of 500-1000 lx and a photocycle of 12 hours of light and 12 hours of darkness per day; control ammonia nitrogen ≤0.1 mg / L and nitrite ≤0.05 mg / L.

[0123] Control group: Traditional and conventional breeding and management methods were used without any targeted adjustments, as detailed below: (1) Natural water quality environment (pH, calcium ion concentration, etc. are not adjusted) and no concealed structures are installed.

[0124] (2) Feed twice a day, with each feeding amount being 2-3% of body weight. Use conventional mixed feed (a mixture of high-protein feed (fish, clams) and low-protein feed (corn, soybean cake)).

[0125] (3) No specific light, temperature and salinity control measures.

[0126] The experimental results are shown in Table 9 below. The molting success rate of the experimental group reached 95.0% (95 animals successfully molted), which is 27.0 percentage points higher than that of the control group (68.0%, 68 animals successfully molted). The growth rate of new shell hardness was 42.3%, which is significantly higher than that of the control group (28.5%). Specifically, the average hardness of the plastron in the experimental group was 28.6 Shore A (HA) on the first day after molting, which increased to 40.7 Shore A (HA) on the tenth day, while the hardness in the control group only increased from 27.9 Shore A to 35.9 Shore A. This indicates that the precise increase in calcium ion concentration and nutritional support in the targeted regulation provided sufficient raw materials for the synthesis of calcium carbonate in the new shell, effectively promoting the hardening and development of the new shell.

[0127] The experimental group achieved a feed utilization rate of 76.8% (total weight gain of 3126g, total feed intake of 4070g), a 24.3 percentage point increase compared to the control group's 52.5% (total weight gain of 1848g, total feed intake of 3520g). This improvement was attributed to the use of high-protein live bait (fish, shrimp, and shellfish) and a precise feeding regimen of three times a day, with each feeding representing 3-4% of the crab's body weight. This approach matched the high metabolic demands of mud crabs during the pre-molting period while minimizing feed waste. Furthermore, the experimental group achieved a 97.9% survival rate (93 crabs survived) 10 days after molting, significantly higher than the control group's 82.4% (56 crabs survived). The stable calcium ion concentration in the water (92.0%) was also significantly better than the control group's 65.0%, demonstrating the crucial role of a stable water environment and concealed structural features in reducing stress and improving the health of mud crabs.

[0128] The pre-molting stage is crucial for mud crabs to accumulate nutrients and build a new shell. Environmental parameters and aquaculture management measures must be precisely matched to their physiological needs: a water pH of 7.8-8.2 is suitable for mud crab growth and new shell synthesis; excessive acidity or alkalinity will affect calcium absorption and enzyme activity; a temperature of 24-26℃ and a salinity of 12-18% can maintain a stable metabolic rate for mud crabs, avoiding stress responses caused by temperature or salinity fluctuations; calcium ions are the core component of calcium carbonate in the new shell, and a concentration of 400-500 mg / kg can meet the calcium requirements for new shell synthesis; dissolved oxygen of 5.5-6.0 mg / L can ensure oxygen supply during periods of high feeding; setting up concealed structures and controlling the shading rate to 60-70% can reduce mutual interference and cannibalism among mud crabs, thus reducing stress responses; feeding three times a day with 3-4% high-protein feed per feeding can match the high feeding needs of mud crabs during the pre-molting stage, ensuring sufficient protein and energy intake; 500-1000 The 12L:12D light intensity and photoperiod align with the natural growth rhythm of mud crabs, promoting stable physiological metabolism. Maintaining low concentrations of ammonia nitrogen and nitrite avoids damage to the hepatopancreas and gills, ensuring the crabs' health. These combined regulatory measures create a suitable environment for the early molting stage of mud crabs. This approach aims to create the optimal environment for growth and nutrient accumulation, specifically addressing the crabs' core needs for nutrition, water quality, and environment during this phase. It promotes normal new shell development, strengthens the crabs' constitution, and reduces problems such as abnormal growth and molting difficulties caused by unsuitable environments or insufficient nutrition, laying a solid foundation for successful molting later.

[0129] Table 9. Data on the effectiveness of management measures after early warning of molting.

[0130] Note: 1. The hardness of the plastron was measured using a Shore A hardness tester. The plastron region below the longest serration on both sides of the cephalothorax was measured for each crab, and the average value was taken for each measurement; 2. The calcium ion concentration in the water was measured twice a day at 9:00 AM and 5:00 PM using a calcium ion analyzer, and the average value for that day was taken; 3. Total weight gain = total weight of crabs at the end of the experiment - total weight of crabs at the beginning of the experiment; 4. The total amount of feed was the sum of the dry weight of the feed actually fed during the experiment.

[0131] Example 7 This embodiment provides an effectiveness verification of emergency intervention measures near the molting stage, verifying the impact of measures such as increasing temperature, reducing light exposure, and increasing dissolved oxygen during the molting stage on the molting process and molting mortality. The specific experimental steps are as follows.

[0132] Two hundred mud crabs were selected and determined to be in the molting stage (expected to molt within 1-2 days) according to the method of Example 2 of this invention. The size was the same as in Example 4. The experimental period was 5 days, and the molting time and molting mortality rate were recorded.

[0133] Experimental group: The emergency control measures for the period nearing molting according to the present invention were adopted, as follows: (1) The water temperature is increased by 2-3℃ at a heating rate of 0.3℃ per hour, and finally stabilized at 26-28℃.

[0134] (2) Cover with a blackout cloth to reduce the light intensity to 100-200 lx and adjust the light cycle to 10 hours of light and 14 hours of darkness.

[0135] (3) Add 0.8 g / m³ of water to the water body according to the ratio of usage to water volume. 3 Vitamin C at 0.25g / m 3 EDTA-2Na.

[0136] (4) Adjust the dissolved oxygen content in the water to 6.5-7.5 mg / L and stop feeding.

[0137] Control group: Traditional breeding management was adopted without any emergency intervention measures, as detailed below: (1) Maintain the original water temperature (24-26℃) and light intensity (natural light, about 5000 lx).

[0138] (2) Do not add vitamin C and EDTA-2Na, maintain dissolved oxygen at 5.0-5.5 mg / L, and feed normally.

[0139] The experimental results are shown in Table 10 below. The average molting time in the experimental group was 45.2 minutes, which was 33.4 minutes shorter than the 78.6 minutes in the control group. The molting mortality rate was only 4.0% (4 deaths), far lower than the 32.0% (32 deaths) in the control group. The incidence of stress response was 8.0% (8 animals), which was 37.0 percentage points lower than the 45.0% (45 animals) in the control group. The molting success rate reached 96.0%, significantly better than the 68.0% in the control group. At the same time, the hardening rate of the new shell in the experimental group was 2.3 hours / hardness unit, which was significantly faster than the 3.8 hours / hardness unit in the control group. This indicates that the emergency intervention measures not only promoted successful molting but also provided favorable conditions for the development of the new shell.

[0140] During the molting period, mud crabs are physiologically sensitive and have weak adaptability. Various control measures are precisely implemented around "reducing stress, promoting molting, and ensuring survival": the temperature is increased to 26-28℃ at a rate of 0.3℃ per hour to gradually increase the metabolic rate and molting hormone secretion, avoiding rapid temperature increase stress; the light intensity is reduced to 100-200 lx with a 10L:14D photoperiod to match their photophobic behavior and reduce external stimulation; vitamin C and EDTA-2Na are added to enhance stress resistance and chelate heavy metal ions, respectively, to protect the fragile epidermis during molting; dissolved oxygen is increased to 6.5-7.5 mg / L to meet the surge in oxygen demand during molting and avoid molting interruption due to hypoxia; feeding is stopped to reduce the burden on the digestive tract and pollution from uneaten feed, ensuring clean water quality. These measures create a low-stress, highly adaptable molting environment, effectively reducing the risks of stress response, hypoxia, and water pollution, shortening molting time, reducing problems such as molting difficulties, limb loss, and death, and significantly improving the molting success rate and post-molting survival rate. This has important practical guiding significance for the large-scale farming of mud crabs.

[0141] Table 10. Data on the effectiveness of emergency intervention measures near the molting period.

[0142] Note: 1. Molting time and new shell hardness data were monitored and recorded 24 hours a day using a Huawei full-color 4K high-definition camera system. Hardness measurements were taken from the central area of ​​the plastron, with three measurements taken each time and the average value taken. 2. Stress response was determined by a combination of video playback and on-site observation, focusing on recording abnormal struggles, appendage breakage, and incomplete shedding of the old shell during molting. 3. The time to complete hardening was started from the completion of molting (when the chelipeds were completely removed from the old shell) until the difference between two consecutive hardness measurements (12 hours apart) was less than 5%.

[0143] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for predicting the molting period of mud crabs, characterized in that, The molting period includes the pre-molting stage and the near-molting stage; the method includes the following steps: acquiring behavioral and morphological data of mud crabs, and predicting the pre-molting and near-molting stages of mud crabs; the behavioral data includes the feeding behavior, activity frequency, respiratory frequency, and wiping behavior of mud crabs; the morphological data includes the appendage joint characteristics, cephalothorax edge characteristics, abdominal umbilicus setae length, abdominal umbilicus color, abdominal morphological changes, and carapace hardness of mud crabs.

2. The method according to claim 1, characterized in that, The changes in abdominal morphology include variations in the vertical distance between the central part of the plastron and the posterior edge of the cephalothorax.

3. The method according to claim 1, characterized in that, The prediction of the pre-molting stage is based on the feeding behavior, appendage joint characteristics, cephalothorax edge characteristics, abdominal umbilical setae length, abdominal umbilical color, and abdominal morphological changes of the mud crab; the pre-molting stage of the mud crab is 12-15 days before molting.

4. The method according to claim 3, characterized in that, When a mud crab meets at least 3 of the following conditions (1)-(5), it is predicted that the mud crab is entering the pre-molting stage; (1) The daily food intake of mud crabs is 20% or more higher than the normal baseline level, and they prioritize protein intake; the normal baseline level is the average daily food intake of mud crabs 7-20 days after molting; the protein includes at least one of fish, shrimp and shellfish. (2) The diameter of the limb joint increases by 3% or more compared to the non-molting period; at the same time, the epidermal color value at the joint decreases by 10% or more compared to the normal area; the normal area is the area adjacent to the joint. (3) The posterior and lateral margins of the cephalothorax of the blue crab form continuous raised lines, and the width of the raised lines is greater than or equal to 0.5 mm; (4) The length of the bristles on the outer edge of the abdomen of the mud crab increases by 20% or more compared with the non-molting period, when the color value of the abdomen navel L is ≥80 and the b value is 20-30; the color values ​​of the abdomen navel L and b are obtained using the CIELab color space. (5) The vertical distance between the central part of the plastron and the posterior edge of the cephalothorax increases by 5% or more compared to the non-molting period when the body width is similar; the non-molting period is 7-15 days after molting.

5. The method according to claim 1, characterized in that, The molting approach period is used to predict when mud crabs will enter the molting approach period based on activity frequency, shell hardness, respiratory frequency, and wiping behavior; the molting approach period is 1-2 days before the mud crab molts.

6. The method according to claim 5, characterized in that, The hardness of the carapace includes the hardness of the abdominal plate area below the longest serrations on both sides of the cephalothorax of the blue crab.

7. The method according to claim 5, characterized in that, When a mud crab enters the pre-molting stage, if it meets all of the following characteristics (1)-(4), it is predicted that the mud crab is about to enter the molting stage. (1) After the mud crab has been lying still for 24-48 hours, the number of times it moves per hour is 300% or more higher than during the lying-still period; and the crab appears in an upright position with its appendages at least 5 times per hour, each time lasting at least 15 seconds. (2) The hardness of the abdominal plate below the longest serration on both sides of the cephalothorax of the mud crab is reduced by 20% or more compared with the non-molting period; (3) The number of times the gill covers open and close is counted. The breathing rate of the blue crab reaches 13-16 times per minute. (4) The number of times the mud crab scrapes the seam between the abdominal carapace and the carapace with its claws shall not be less than 20 times per hour, each time lasting not less than 10 seconds, accompanied by the cleaning action of the walking legs on the surface of the body, and the total daily wiping time shall not be less than 5 minutes.

8. The method according to claim 1, characterized in that, The mud crabs mentioned include mud crabs such as mud crab, mud crab, mud crab, mud crab or hybrids thereof.

9. A method for farming mud crabs, characterized in that, The method includes the following steps: after predicting the pre-molting stage using the method for predicting the molting period of mud crabs as described in claim 1, perform any one or more of the following steps (1)-(5): (1) Increase the ambient shading rate to 60-70%; (2) Increase the calcium ion concentration in the water to 400-500 mg / kg and maintain dissolved oxygen at 5.5-6.0 mg / L; (3) Increase the feeding frequency to 3-5 times, with a single feeding amount of 3-4% of the body weight of the mud crab; the feeding includes feeding with feed from at least one source of fish, shrimp and shellfish; (4) Adjust the light intensity to 500-1000 lx; (5) Control the ammonia nitrogen in the water body to ≤0.1mg / L and the nitrite to ≤0.05mg / L.

10. A method for farming mud crabs, characterized in that, The method includes the following steps: after predicting the approaching molting period using the method for predicting the molting period of mud crabs as described in claim 1, perform any one or more of the following steps (1)-(6): (1) Raise the water temperature to 26-28℃; (2) Adjust the light intensity to 100-200 lx; (3) Adjust the photoperiod to 8-10 hours of light and 14-16 hours of darkness; (4) Add 0.5-1 g / m³ to the water body according to the ratio of usage to water volume. 3 Vitamin C at 0.1-0.5g / m 3 EDTA-2Na; (5) Adjust the dissolved oxygen in the water to 6.5-7.5 mg / L; (6) Stop feeding.

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