Method for promoting growth of young lutjanus erythropterus by adjusting flow velocity and application

Abstract

The invention discloses a method for promoting growth of young lutjanus erythropterus by adjusting the flow rate and application. Belongs to the technical field of aquaculture. According to the method, flow velocity parameters of an adaptation period, a promotion period and a stable growth period are accurately set according to the physiological requirements of the young lutjanus erythropterus in different growth stages through staged flow velocity regulation and growth and physiological index dynamic optimization, and the young lutjanus erythropterus can be rapidly and accurately bred through periodic variable-speed water flow stimulation and flow velocity regulation based on the contents of liver glucose, lactic acid and cortisol. And accurate control of the flow velocity of aquaculture water is realized. The method has the advantages of being convenient to operate, accurate in regulation and control and the like, the problems of energy waste and stress of traditional fixed-flow-speed breeding are solved, a new efficient and environment-friendly way is provided for healthy breeding and large-scale production of the lutjanus erythropterus, and the method has important significance in improving the economic benefits and the technical level of aquaculture.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of aquaculture, more particularly, it relates to a method for promoting the growth of red sea perch juvenile fish by adjusting flow rate and application thereof. BACKGROUND

[0002] Red sea perch (Lutjanus erythropterus) is an important marine aquaculture economic fish in China. Due to its delicious meat and rich nutrition, it has a strong market demand. With the expansion of the scale of aquaculture, how to improve the efficiency of aquaculture, especially the growth performance in the key stage of juvenile fish, has become the core problem of the development of the industry.

[0003] At present, the culture of red sea perch has formed a series of technical specifications and management strategies. In the aspect of environmental control, the relevant standards clearly define the range of key water quality parameters such as water temperature (23℃~30℃), salinity (20-30) and dissolved oxygen (≥5mg / L). In terms of nutrition supply, research has established a formula of compound feed with crude protein content of 35-45%, and has explored the positive effect of immune enhancers such as Chinese herbal medicine on improving the weight gain rate (up to 65.4%) and disease resistance. In the aspect of seed cultivation, the technical scheme optimizes the rotifer feeding density (10-20 individuals / mL) and the first time of feeding (16-22 days old), aiming to improve the growth and survival rate of larvae.

[0004] However, the existing technical system has significant limitations. The current culture mode generally focuses on the optimization of static environmental factors (such as water temperature, salinity) and the implementation of fixed feeding strategies, but has long neglected the water flow rate, which is a crucial environmental factor in the natural habitat of fish (such as reef and shallow sea). In nature, red sea perch juveniles will encounter dynamically changing water flow, which directly affects their movement behavior, energy metabolism allocation and physiological state. Improper flow rate will force the juveniles to consume excessive energy to resist the water flow, leading to increased stress level and inhibited growth; while appropriate flow rate stimulation can promote their movement ability and optimize metabolic efficiency, thus benefiting the improvement of growth performance. Unfortunately, the existing culture facilities generally adopt static or constant flow rate mode, lacking dynamic flow rate regulation strategies based on the physiological needs and behavioral feedback of juveniles at different growth stages.

[0005] Although individual studies have begun to focus on the static, forward and backward behaviors of red sea perch juveniles near artificial reefs, research on associating these specific behavior patterns with scientific flow rate regulation is still in the blank. In addition, the existing technology often applies environmental control, nutrition regulation and water flow management separately, without forming a systematic solution of synergistic optimization. For example, appropriate water flow may enhance the activity of juveniles to improve their feeding activity and feed utilization rate, but this synergistic effect has not been effectively tapped and utilized.

[0006] Therefore, developing a method for precise and dynamic flow rate control based on the growth characteristics, swimming ability, and real-time behavioral feedback of juvenile redfin snapper is of great and urgent practical significance for breaking through the technical bottlenecks of existing aquaculture models and comprehensively improving the growth rate, health level, and economic benefits of juvenile fish. Summary of the Invention

[0007] In view of this, the present invention develops a method and application for promoting the growth of juvenile redfin snapper by adjusting the flow rate. By precisely controlling the water flow rate and combining it with environmental control and nutritional regulation, the growth of juvenile redfin snapper is effectively promoted.

[0008] The primary objective of this application is to provide a method for promoting the growth of juvenile redfin snapper by regulating flow rate, comprising the following steps: S1. Determination of critical swimming speed: The absolute critical swimming speed Ua and relative critical swimming speed Ur of juvenile redfin snapper were determined by step speed test. The relative critical swimming speed Ur is the ratio of the absolute critical swimming speed Ua to the body length Bl. S2. Determine the maximum acclimatization speed VRM: Based on the relative critical swimming speed Ur measured in step S1, determine the limiting flow velocity value. Set multiple increasing flow velocity gradients within the range of 0 to the limiting flow velocity value to acclimatize juvenile fish. Observe and count the time juvenile fish remain still, move forward, and move backward at each flow velocity. Select the highest flow velocity where the forward movement time is greater than the backward movement time and set it as the maximum acclimatization speed VRM. S3. Phased Flow Rate Control: Throughout the entire rearing cycle, the water flow rate is dynamically adjusted in three phases to regulate the growth of juvenile redfin snapper, as detailed below: (a) Days 0-3, growth adaptation period: incremental variable flow stimulation was used. The initial flow rate was maintained at 0.5 Bl / s for 12 hours, and the rest of the time was kept still. Then, the flow rate was increased by 0.2 Bl / s each day until it reached 0.3 VRM. The flow rate was maintained for 12 hours each day, and the rest of the time was kept still. (b) Days 4-21, growth promotion period: periodic variable-speed water flow stimulation is used, specifically: From 8:00 to 12:00 daily, the flow rate is maintained at VRM; From 12:00 to 16:00 daily, the flow rate is reduced to 0.5 VRM; From 16:00 to 20:00 daily, the flow rate rebounded to 0.75 VRM; From 20:00 to 8:00 the next day, the flow rate is maintained at 0.25 VRM; (c) From day 22 to the end of the culture, during the stable growth period: constant water flow stimulation was used, and the flow rate was maintained at 0.5 VRM; when the body length of the juvenile fish was monitored to be more than 20% of the initial body length, the VRM value detection experiment was carried out again according to the new body length, and the S3 staged flow rate regulation was carried out again. S4. Dynamic optimization based on physiological indicators: During the aquaculture process, the liver glucose, lactic acid and cortisol content and daily growth rate of juvenile fish are monitored regularly, and the flow rate strategy is dynamically adjusted based on the monitoring results. S5. Supporting aquaculture management: Implement feeding and water quality management measures in conjunction with flow rate control.

[0009] As a preferred technical solution, the method for determining the absolute critical swimming speed in step S1 is as follows: multiple juvenile fish are placed in a flow rate of 0.5 BL / s for 30 min, and then the flow rate is increased by 0.5 BL / s every 30 min until the fish is exhausted. The fish is considered exhausted when it stays on the downstream honeycomb net for ≥20 s. The formula for calculating the absolute critical swimming speed Ua is: Ua = U + (ΔU * t / ΔT), where U is the highest speed of the fish during the entire time interval, ΔU is the speed increment, t is the sustainable swimming time of the fish at the highest flow rate, and ΔT is the specified time interval.

[0010] As a preferred technical solution, the limiting flow velocity value in step S2 is equal to the relative critical swimming velocity.

[0011] As a preferred technical solution, in step S2, "still" means that the fish remains in a fixed position and does not move with the water flow for more than 5 seconds; "moving forward" means that the fish actively swims forward against the current for a distance greater than 10cm; and "moving backward" means that the fish is swept away by the water flow or actively moves backward with the current for a distance greater than 10cm.

[0012] As a preferred technical solution, in step S4, the dynamic optimization based on physiological indicators specifically includes: Monitor the liver glucose, lactic acid, and cortisol levels, as well as the daily growth rate of the juvenile fish, every 7 days. When any of the following conditions are met, pause variable-speed stimulation and maintain the flow rate at 0.3 VRM until the indicators recover: Glucose (GLU) content <0.6 mmol / g protein; GLU reflects the energy metabolism status of fish, and a value below the threshold indicates poor energy metabolism status.

[0013] Lactic acid LD content >1.2 mmol / g protein; lactic acid reflects the intensity of anaerobic metabolism, and when it is higher than the threshold, it indicates that the fish is under stress or has excessive energy consumption.

[0014] Cortisol (COR) content >30 ng / m³ per gram of protein; COR is a core hormone of stress response, and a level above the threshold indicates that the fish is under stress.

[0015] Meanwhile, adjustments are made based on the daily growth rate: when the daily growth rate is ≥1.2% / day, the current flow rate strategy is maintained; when the daily growth rate is <1.2% / day, the current flow rate is increased by 0.1 Bl / s to stimulate the flow.

[0016] As a preferred technical solution, the formula for calculating the daily growth rate is as follows: Daily growth rate = (W t W0) / (W0×t)×100%, where W t W0 represents the average weight of the juvenile fish after rearing (g); W0 represents the average weight of the juvenile fish before rearing (g); and t represents the number of rearing days.

[0017] As a preferred technical solution, in step S5, the supporting aquaculture management includes: Feed the fish daily when the flow rate is ≤0.3 VRM. Keep the flow rate ≤0.5 Bl / s for 30 minutes after feeding. Gradually increase the flow rate to the corresponding stage standard 1 hour after feeding. The daily feeding amount is 3%-5% of the fish's body weight. Use floating pellets with a particle size of 0.3-0.5mm and remove any uneaten feed before the flow rate increases. Replace 40% of the aquaculture water every 2 days; maintain water temperature at 28±1℃, dissolved oxygen ≥7.00 mg / L, and test ammonia nitrogen ≤0.5 mg / L and nitrite <0.1 mg / L daily.

[0018] Another object of this application is to provide the application of the above-described method in promoting the growth of juvenile redfin snapper.

[0019] As can be seen from the above technical solution, compared with the prior art, the present invention has the following beneficial effects: This invention achieves precise control of the aquaculture water flow rate by staged regulation of the water flow rate and dynamic optimization based on growth and physiological indicators. It precisely sets flow rate parameters for the adaptation, promotion, and stable growth phases of juvenile redfin snapper, targeting their physiological needs at different growth stages. Through periodic variable-speed water flow stimulation and flow rate regulation based on liver glucose, lactic acid, and cortisol levels, it achieves accurate control of the aquaculture water flow rate. This method offers advantages such as ease of operation and precise regulation, avoiding the energy waste and stress problems associated with traditional fixed-flow-rate aquaculture. It provides a new, efficient, and environmentally friendly approach for the healthy aquaculture and large-scale production of redfin snapper, and is of great significance for improving the economic benefits and technological level of aquaculture. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0021] Figure 1 The flowchart shows a method for regulating flow rate to promote the growth of juvenile redfin snapper.

[0022] Figure 2 Example 1: The percentage of movement states of redfin snapper under different flow velocities.

[0023] Figure 3 Example 1: Average weight of redfin snapper after 30 days of culture in different groups.

[0024] Figure 4 Example 1: Daily growth rate of redfin snapper after 30 days of culture in different groups.

[0025] Figure 5 Example 2: Evaluation of fish movement behavior under different flow rates.

[0026] Figure 6 Example 2: Evaluation of fish movement behavior when redetermining the critical swimming speed.

[0027] Figure 7 Example 2: Average weight of redfin snapper after 44 days of culture in different groups.

[0028] Figure 8 Example 2: Daily growth rate of redfin snapper after 44 days of culture in different groups. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Construction of the aquaculture system used in the embodiments of the present invention A fish swimming ability testing circulating water tank (model FBT-10X) was used for flow rate regulation experiments. The test section dimensions were 50cm×50cm×120cm, and the test flow rate range was 5-120cm / s. It can achieve timed operation from 1min to 999min and constant speed intermittent operation from 10-120cm / s. The water level in the circulating water tank was 10cm lower than the top of the tank. The water flow was powered by an underwater propulsion device. A honeycomb flow stabilizer was installed to form a stable water flow. The water flow speed was adjusted by the machine power. Network cameras were installed in front of and above the circulating water tank to observe and record the behavior of juvenile fish. A thermometer and a dissolved oxygen meter were installed on the side of the tank to monitor the temperature and dissolved oxygen levels in real time.

[0031] Experimental Materials: Healthy juvenile redfin snapper were selected and temporarily housed in a factory-style recirculating aquaculture system. The juveniles' body length and weight were monitored regularly. The seawater temperature was maintained at 28±2℃, and dissolved oxygen was ≥ 7.00 mg / L. Fish were fed to satiety at 8:30 AM and 5:30 PM daily, and 40% of the aquaculture water was replaced every two days. The experimental fish were housed for 7 days, with feeding stopped 24 hours before the experiment. Before the experiment, the body length (in cm) of the fish was measured, and juveniles were randomly selected and placed in the recirculating aquaculture tank. After the fish had recovered from stress, subsequent experimental procedures were carried out on the juveniles. Water temperature and dissolved oxygen were monitored in real time throughout the experiment.

[0032] All embodiments of this invention are based on the body length of juvenile redfin snapper, and the flow rate regulation is studied using multiples of body length per second as the unit of flow rate, with the unit being Bl / S, where Bl is the body length in cm.

[0033] Example 1 A method to promote the growth of juvenile redfin snapper by adjusting the flow rate (body length increase not exceeding 20%). In this example experiment, the juvenile fish had a body length of 9.93±1.02 cm, a body height of 4.23±0.21 cm, and a weight of 15.13±1.78 g, totaling 600 fish. The specific process (…) Figure 1 )as follows: S1, Critical Swimming Speed ​​Determination First, the critical swimming speed of the juvenile fish was monitored. The critical swimming speed can characterize the swimming ability of juvenile redfin snapper and guide the subsequent development of flow rate control strategies. In order to characterize the swimming ability of redfin snapper, a stepped speed test was used to measure its absolute critical swimming speed (Ua) and relative critical swimming speed (Ur).

[0034] Absolute critical swimming speed (Ua) determination: Ten fish were placed in the working area and exposed to a current of 0.5 Bl / s for 30 min to acclimatize. The current was then increased by 0.5 Bl / s every 30 min until exhaustion was achieved. A fish was considered exhausted if it remained on the downstream honeycomb barrier for 20 s. The swimming speed and elapsed time were recorded (Table 1). The 10th fish was considered an outlier and does not represent the group's characteristics. Fish were used only once during the experiment to prevent exhaustion from affecting the results.

[0035] The formula for calculating the absolute critical swimming speed (Ua) is: Ua = U + U×t / t. Where U is the fish's highest speed (cm / s) during the entire time interval (from the start of swimming to exhaustion). U is the velocity increment (cm / s) (initial flow velocity - flow velocity at exhaustion), and t is the sustainable swimming time of the fish at the highest flow velocity (min). t is the specified time interval (min), which is 30 min here.

[0036] The formula for calculating the relative critical swimming speed (Ur) is: Ur = Ua / Bl, where Bl is the body length of the juvenile fish.

[0037] Table 1. Swimming speed, time, and critical swimming speed of the experimental fish

[0038] Results analysis: As shown in Table 1, the absolute critical swimming speed of the redfin snapper is 53.04±5.27 cm / s, and the relative critical swimming speed is 5.34±0.53 Bl / s.

[0039] S2. Determine the maximum acclimatization rate (VRM) Based on the relative critical swimming speed Ur measured in step S1, the limiting flow velocity was determined to be 5Bl / s. According to this limiting flow velocity, the flow velocities were divided into groups at 1Bl / s intervals from 0 to 5Bl / s: 0Bl / s, 1Bl / s, 2Bl / s, 3Bl / s, 4Bl / s, and 5Bl / s. Before each experiment, 10 juvenile redfin snapper were placed in a circulating water tank and acclimatized for 30 minutes at a low flow velocity (1Bl / s). They were then acclimatized for 2 hours at the aforementioned flow velocities to assess their movement behavior. The specific assessment process is as follows: Fish movement behavior was categorized into three states: stationary (maintaining position for more than 5 seconds), forward movement (fish actively moving forward against the current for a distance greater than 10 cm), and backward movement (fish being swept away by the current or actively moving backward with the current for a distance greater than 10 cm). For each experiment, five fish were randomly selected, and videos of more than ten different movement states were included. Each experimental group was repeated three times.

[0040] The time percentages of three motion states are compared and analyzed. The calculation method for the time percentage of each motion state is as follows: For any given water flow velocity (e.g., 2 Bl / s): Percentage of time for a certain motion state = (Total time observed for this state at this flow rate) / (Total time observed for all states at this flow rate) × 100%.

[0041] Results analysis, by Figure 2 It can be seen that the percentage of time spent stationary, moving forward, and moving backward in the redfin snapper is related to the flow velocity. At a flow velocity of 3 Bl / s, the forward movement time accounts for 21.14%, and the backward movement time accounts for 15.63%, meaning the forward movement time is longer than the backward movement time. At a flow velocity of 4 Bl / s, the forward movement time accounts for 21.24%, and the backward movement time accounts for 25.28%, meaning the forward movement time is shorter than the backward movement time. Therefore, 3 Bl / s is chosen as the maximum acclimatization speed, i.e., VRM is 3 Bl / s.

[0042] S3 staged flow rate regulation and S4 dynamic optimization based on physiological indicators The experimental fish were randomly divided into three groups of 60 fish each: a control group, a fixed flow rate group, and an invention group (the phased flow rate control group of this invention). The control group maintained a static flow rate of 0 B1 / s throughout the experiment; the fixed flow rate group maintained a constant flow rate of 1 B1 / s throughout the experiment; and the invention group was cultured according to the following phased flow rate control strategy: (a) Adaptation period (0-3 days): The flow rate is maintained at 0.5 Bl / s initially, with a buffer period of 12 hours, and the fish remain still for the rest of the time. From the second day onwards, the flow rate is increased by 0.2 Bl / s daily until it reaches 0.9 Bl / s, allowing the juvenile fish to adapt to the water flow environment. This flow rate is maintained for 12 hours each day, and the fish remain still for the rest of the time.

[0043] (b) Growth promotion period (4-21 days): Promote the movement and metabolism of juvenile fish from 8:00 to 12:00 (3.0 Bl / s), reduce energy consumption from 12:00 to 16:00 (1.5 Bl / s), continuously stimulate muscle development of juvenile fish from 16:00 to 20:00 (2.25 Bl / s), and ensure that juvenile fish get rest from 20:00 to 8:00 the next day (0.75 Bl / s). Adjust the flow rate according to the above cycle.

[0044] On day 7, 5 fish were taken for testing: The liver GLU of the juvenile fish in this invention group was 1.12±0.15 mmol / g protein, LD was 0.78±0.09 mmol / g protein, COR was 22.5±3.2 ng / mg protein, and the daily growth rate was 1.2% / day. The current strategy will be maintained. On day 14, five fish were harvested for testing: the LD in the constant flow rate group increased to 1.12 ± 0.11 mmol / g protein, and flow stimulation was suspended for 2 days. In the juvenile group of this invention, the liver GLU was 1.11 ± 0.12 mmol / g protein, the LD was 0.82 ± 0.12 mmol / g protein, the COR was 20.4 ± 2.2 ng / m² / g protein, and the daily growth rate reached 1.6% / day, maintaining the growth rate.

[0045] On day 21, five fish were harvested for testing: In the constant flow rate group, the LD (lower protein concentration) increased to 1.22 ± 0.08 mmol / g protein, and flow rate stimulation was suspended for 2 days. In the juvenile group of this invention, the liver GLU was 0.92 ± 0.21 mmol / g protein, the LD was 0.90 ± 0.08 mmol / g protein, the COR (coefficient of regeneration) was 23.2 ± 3.1 ng / m³ / g protein, and the daily growth rate reached 1.3% / day, maintaining the growth rate.

[0046] Table 2. Physiological and growth indicators of each group at different time points.

[0047] (c) Stable growth period (22-30 days): The average body length of the juvenile fish in this invention group increased to 11.6 cm, and the body length growth did not exceed 20%, so the flow rate was maintained at 1.5 B1 / s.

[0048] S5, Supporting Aquaculture Management During the experiment, feeding was conducted daily at 7:00 AM, with feeding done when the flow rate was maintained at or below 0.9 Bl / s. The flow rate was kept ≤ 0.5 Bl / s for 30 minutes after feeding, and then gradually increased to the corresponding standard flow rate 1 hour later. Floating pellets with a particle size of 0.3-1.0 mm were used as feed, with a daily feeding amount of 3-5% of the fish's body weight. Excess food and residue in the tank were removed before the flow rate increased. 40% of the aquaculture water was changed every 2 days. While adjusting the flow rate, the water temperature was maintained at 28±1℃, dissolved oxygen ≥ 7.00 mg / L, and ammonia nitrogen ≤ 0.5 mg / L and nitrite < 0.1 mg / L daily.

[0049] To verify the effectiveness of the method in Example 1, the growth status of juvenile redfin snapper was measured after 30 days of culture.

[0050] Ten juvenile redfin snapper were randomly selected after 30 days of rearing. Their body weight was measured, and their daily growth rate was calculated. The experimental results are as follows: Figure 3 and Figure 4 As shown.

[0051] Results Analysis: Figure 3 and Figure 4 It can be seen that the average weight of the juvenile redfin snapper in the control group was 19.6±3.2 g, and its daily growth rate was 0.98% / day; the average weight of the juvenile redfin snapper in the fixed flow rate group was 20.7±3.8 g, and its daily growth rate was 1.23% / day; and the average weight of the juvenile redfin snapper in the present invention group was 22.2±4.5 g, and its daily growth rate was 1.56% / day.

[0052] The results show that the phased flow rate regulation process has a higher consistency with the liver physiological indicators compared with the fixed flow rate group, indicating that the method of the present invention reduces stimulation. At the same time, the method of the present invention has the best effect on improving the growth rate of juvenile red snapper, and is an effective way to regulate the growth of juvenile red snapper based on flow rate.

[0053] Example 2 The effect of flow rate regulation on the growth of juvenile redfin snapper (body length increase exceeding 20%). In this example, the juvenile fish had a body length of 9.21±1.05 cm, a body height of 3.97±0.32 cm, and a weight of 12.43±1.35 g, with a total of 600 fish.

[0054] S1, Critical Swimming Speed ​​Determination First, the critical swimming speed of the juvenile fish was monitored. The critical swimming speed can characterize the swimming ability of juvenile redfin snapper and guide the subsequent development of flow rate control strategies. In order to characterize the swimming ability of redfin snapper, a stepped speed test was used to measure its absolute critical swimming speed (Ua) and relative critical swimming speed (Ur).

[0055] Determination of absolute critical swimming speed (Ua): Ten fish were placed in a circulating water tank and adapted to a flow rate of 0.5 Bl / s for 30 min. Then, the flow rate was increased by 0.5 Bl / s every 30 min until the fish were stuck in the downstream net for 20 s. The swimming speed and time were recorded (Table 3). The fish were used only once during the experiment and were not reused to prevent energy consumption from affecting the experimental results.

[0056] The formula for calculating the absolute critical swimming speed (Ua) is: Ua = U + U×t / t. Where U is the highest velocity (cm / s) of the fish during the entire time interval. U represents the velocity increment (cm / s), and t represents the time (min) the fish can swim sustainably at the highest current velocity. t is the specified time interval (min).

[0057] The formula for calculating the relative critical swimming speed (Ur) is: Ur = Ua / Bl, where Bl is the body length of the juvenile fish.

[0058] Table 3. Swimming speed, time, and critical swimming speed of the experimental fish

[0059] Results analysis: As shown in Table 3, the absolute critical swimming speed was calculated to be 52.65±5.12 cm / s, and the relative critical swimming speed was 5.68±0.57 Bl / s.

[0060] S2. Determine the maximum acclimatization rate (VRM) Based on the relative critical swimming speed Ur measured in step S1, the limiting flow velocity was determined to be 6Bl / s. According to this limiting flow velocity, the flow velocities were divided into groups at 1Bl / s intervals from 0 to 6Bl / s: 0Bl / s, 1Bl / s, 2Bl / s, 3Bl / s, 4Bl / s, 5Bl / s, and 6Bl / s. Before each experiment, 10 juvenile redfin snapper were placed in a circulating water tank and acclimatized at a low flow velocity (1Bl / s) for 30 minutes. They were then acclimatized for 2 hours at the aforementioned flow velocities to assess their movement behavior. The specific assessment process is as follows: Fish movement behavior was categorized into three states: stationary (maintaining position for more than 5 seconds), forward movement (fish actively moving forward against the current for a distance greater than 10 cm), and backward movement (fish being swept away by the current or actively moving backward with the current for a distance greater than 10 cm). For each experiment, five fish were randomly selected, and videos of more than ten different movement states were included. Each experimental group was repeated three times.

[0061] The time percentages of three motion states are compared and analyzed. The calculation method for the time percentage of each motion state is as follows: For any given water flow velocity (e.g., 2 Bl / s): The percentage of time spent in a particular motion state = (total time observed in this state at that flow rate) / (total time observed in all states at that flow rate) × 100%. Determined through motion behavior assessment.

[0062] Results Analysis: Results analysis, by... Figure 5 It can be seen that at a current speed of 3Bl / s, the redfin snapper spends 22.35% of its time moving forward and 14.72% moving backward, with the forward movement time being longer than the backward movement time; at a current speed of 4Bl / s, the forward movement time is 20.11% and the backward movement time is 26.34%, with the forward movement time being shorter than the backward movement time. Therefore, 3Bl / s is chosen as the maximum taming speed, i.e., VRM is 3Bl / s.

[0063] S3 staged flow rate regulation and S4 dynamic optimization based on physiological indicators The experimental fish were randomly divided into three groups of 60 fish each: a control group, a fixed flow rate group, and an invention group (the phased flow rate control group of this invention). The control group maintained a static flow rate of 0 B1 / s throughout the experiment; the fixed flow rate group maintained a constant flow rate of 1 B1 / s throughout the experiment; and the invention group was cultured according to the following phased flow rate control strategy: (a) Adaptation period (0-3 days): The flow rate is maintained at 0.5 Bl / s initially, with a buffer period of 12 hours, and the fish remain still for the rest of the time. From the second day onwards, the flow rate is increased by 0.2 Bl / s daily until it reaches 0.9 Bl / s, allowing the juvenile fish to adapt to the water flow environment. This flow rate is maintained for 12 hours each day, and the fish remain still for the rest of the time.

[0064] (b) Growth promotion period (4-21 days): The flow rate is adjusted according to the daily cycle of 8:00-12:00 (3.0Bl / s), 12:00-16:00 (1.5Bl / s), 16:00-20:00 (2.25Bl / s), and 20:00-8:00 the next day (0.75Bl / s).

[0065] On day 7, 5 fish were taken for testing: In the juvenile group of this invention, the liver GLU was 1.09±0.06 mmol / g protein, LD was 0.77±0.04 mmol / g protein, COR was 21.8±0.8 ng / mg protein, and the daily growth rate was 1.23% / day. The current strategy was maintained.

[0066] On day 14, five fish were collected for testing: In the constant flow rate group, the LD was 1.14 ± 0.02 mmol / g protein (close to the threshold), and stimulation was paused for 2 days. In the juvenile group of this invention, the liver GLU was 1.13 ± 0.06 mmol / g protein, the LD was 0.80 ± 0.04 mmol / g protein, the COR was 20.7 ± 0.7 ng / m² / g protein, and the daily growth rate reached 1.3% / day. The average body length of the juvenile fish increased to 11.35 ± 0.65 cm (an increase of 23.2%, exceeding 20%), and the experiment was immediately restarted, with VRM calculated.

[0067] Table 4. Physiological and growth indicators of each group at different time points

[0068] (c) Redetermine the critical swimming speed VRM On day 14, the juvenile fish measured 11.35±0.65 cm in length, 5.12±0.87 cm in height, and 28.43±5.67 g in weight.

[0069] The absolute critical velocity and relative critical velocity were re-determined using the same method described above, and the experimental results are shown in Table 5.

[0070] Table 5. Swimming speed, time, and critical swimming speed of the experimental fish.

[0071] The results are shown in Table 5. Under this body length condition, the absolute critical swimming speed of the juvenile fish is 61.31±3.27 cm / s, and the relative critical swimming speed is 5.40±0.32 Bl / s.

[0072] (d) Determination of flow velocity in stages Flow velocity grouping: Based on the relative critical swimming velocity Ur measured in step S1, the limiting flow velocity value is determined to be 5Bl / s. According to the limiting flow velocity value, the flow velocities from 0 to 5Bl / s are divided into groups at intervals of 1Bl / s, namely 0Bl / s, 1Bl / s, 2Bl / s, 3Bl / s, 4Bl / s, and 5Bl / s.

[0073] Motor behavior assessment: At a flow rate of 3Bl / s, the forward movement time accounts for 23.5% and the backward movement time accounts for 13.2%, with the forward movement time being greater than the backward movement time. At a flow rate of 4Bl / s, forward movement accounts for 21.8%, backward movement accounts for 27.5%, and the forward movement time is less than the backward movement time. Figure 6 ).

[0074] Therefore, the maximum acclimatization rate (VRM) during the acclimatization period remains at 3Bl / s.

[0075] (e) Phased flow rate regulation The experimental fish were randomly divided into three groups of 60 each: a control group, a fixed flow rate group, and an invention group (the phased flow rate control group of the present invention). The control group maintained a static flow rate of 0 B1 / s throughout the process; the fixed flow rate group maintained a constant flow rate of 1 B1 / s throughout the process; and the invention group was raised according to the above-mentioned phased flow rate control strategy.

[0076] Adaptation period (0-3 days): The flow rate is maintained at 0.5 Bl / s initially, with a buffer period of 12 hours, and the fish remain still for the rest of the time. From the second day onwards, the flow rate is increased by 0.2 Bl / s daily until it reaches 0.9 Bl / s, allowing the juvenile fish to adapt to the current environment. This flow rate is maintained for 12 hours each day, and the fish remain still for the rest of the time.

[0077] Growth promotion period (4-21 days): The flow rate is adjusted according to the daily cycle of 8:00-12:00 (3.0Bl / s), 12:00-16:00 (1.5Bl / s), 16:00-20:00 (2.25Bl / s), and 20:00-8:00 the next day (0.75Bl / s).

[0078] On day 7, 5 fish were taken for testing: In the juvenile group of this invention, the liver GLU was 1.07±0.03 mmol / g protein, LD was 0.76±0.02 mmol / g protein, COR was 21.7±0.4 ng / mg protein, and the daily growth rate was 1.23% / day. Maintenance strategy; On day 14, five fish were collected for testing: the LD in the constant flow rate group increased to 1.14 ± 0.02 mmol / g protein, close to 1.2, so flow rate stimulation was suspended for 2 days. In the juvenile fish of this invention, the liver GLU was 1.11 ± 0.03 mmol / g protein, the LD was 0.79 ± 0.02 mmol / g protein, the COR was 20.7 ± 0.4 ng / m² protein, and the daily growth rate reached 1.3% / day, maintaining the growth rate.

[0079] On day 21, five fish were taken for testing: In the juvenile group of this invention, the liver GLU was 1.14±0.03 mmol / g protein, LD was 0.81±0.02 mmol / g protein, COR was 20.4±0.4 ng / mg protein, the daily growth rate was 1.36% / day, and the maintenance flow rate was maintained.

[0080] Table 6. Physiological and growth indicators of each group at different time points

[0081] Stable growth period (22-30 days): The average body length of the juvenile fish in this invention group increased to 13.52 cm, an increase of 19.1%, which did not exceed 20%. Therefore, the flow rate was maintained at 1.5 Bl / s.

[0082] S5, Supporting Aquaculture Management During the experiment, feeding was conducted daily at 7:00 AM, with feeding done when the flow rate was maintained at or below 0.9 Bl / s. The flow rate was kept ≤0.5 Bl / s for 30 minutes after feeding, and then gradually increased to the corresponding standard flow rate 1 hour later. Floating pellets with a particle size of 0.3-1.0 mm were used as feed, with a daily feeding amount of 3-5% of the fish's body weight. Excess food and residue in the tank were removed before the flow rate increased. 40% of the aquaculture water was changed every 2 days. During flow rate adjustment, the water temperature was maintained at 28±1 ℃, dissolved oxygen ≥7.00 mg / L, and ammonia nitrogen ≤0.5 mg / L and nitrite <0.1 mg / L were monitored daily.

[0083] To verify the effectiveness of the method in Example 2, the growth status of juvenile redfin snapper was measured after 14+30 days of rearing. Ten juvenile redfin snapper were randomly selected after 44 days of rearing. Their body weight was measured, and their daily growth rate was calculated. The experimental results are as follows: Figure 7 and Figure 8 As shown.

[0084] Results Analysis: Figure 7 and Figure 8 It can be seen that the average weight of the juvenile redfin snapper in the control group was 18.2±3.6 g, and its daily growth rate was 1.05% / day; the average weight of the juvenile redfin snapper in the fixed flow rate group was 19.4±4.3 g, and its daily growth rate was 1.28% / day; and the average weight of the juvenile redfin snapper in the present invention group was 22.4±5.2 g, and its daily growth rate was 1.82% / day.

[0085] The results show that the method of the present invention has the best effect on improving the growth rate of juvenile redfin snapper, and is an effective way to regulate the growth of juvenile redfin snapper based on flow rate.

[0086] Example 3 The effect of flow rate regulation on the growth of juvenile redfin snapper (body length increase <20%, growth rate <1.2% / day). In this example, the juvenile fish had a body length of 8.50±1.01 cm, a body height of 3.12±0.24 cm, and a weight of 10.50±1.50 g, with a total of 600 fish.

[0087] S1, Critical Swimming Speed ​​Determination Table 7. Swimming speed, time, and critical swimming speed of the experimental fish

[0088] Results analysis: The absolute critical swimming velocity (Ua) was measured by the stepped flow velocity test: 45.35±3.45 cm / s; relative critical swimming velocity (Ur): 5.34±0.41BL / s.

[0089] S2. Determine the maximum acclimatization rate (VRM) Flow velocity grouping: Based on the relative critical swimming velocity Ur measured in step S1, the limiting flow velocity value is determined to be 5Bl / s. According to the limiting flow velocity value, the flow velocities from 0 to 5Bl / s are divided into groups at intervals of 1Bl / s, namely 0Bl / s, 1Bl / s, 2Bl / s, 3Bl / s, 4Bl / s, and 5Bl / s.

[0090] Motor behavior assessment: Using the same experimental method, it was observed that at 2BL / s, the forward movement time (20.14%) > the backward movement time (14.63%); while at 3BL / s, the forward movement time (19.24%) < the backward movement time (24.28%).

[0091] Conclusion: 2BL / s is chosen as the maximum acclimatization speed, i.e., VRM = 2BL / s.

[0092] S3 staged flow rate regulation and S4 dynamic optimization based on physiological indicators The experimental groups were identical: Control group: 0 BL / s throughout (static water). Fixed flow rate group: 1 BL / s constant flow rate throughout. Invention group / Experimental group: Applying a "staged flow rate control strategy": (a) Adaptation period (0-3 days): Start with a flow rate of 0.5 BL / s, buffer for 12 hours, then allow to stand still. From the second day onwards, increase the flow rate by 0.2 BL / s daily to 0.3 VRM (i.e., 0.6 BL / s), maintaining this flow rate for 12 hours daily (keeping still for the rest of the time). The purpose is to allow the fish to adapt to the water flow.

[0093] (b) Growth promotion period (4-21 days): Daily flow rate cycle: 8:00-12:00 (2.0 BL / s), 12:00-16:00 (1.0 BL / s), 16:00-20:00 (1.5 BL / s), 20:00-8:00 the next day (0.5 BL / s).

[0094] Day 7: The LD of the invention group was 1.18 ± 0.08 mmol / g protein, close to the threshold of 1.2, and the daily growth rate was 1.1% / day < 1.2%. According to the rule (LD < 1.2, continue to change the flow rate), the daily flow rate cycle became: 8:00-12:00 (2.1 BL / s), 12:00-16:00 (1.1 BL / s), 16:00-20:00 (1.6 BL / s), 20:00-8:00 the next day (0.6 BL / s).

[0095] Day 14: Inventive group LD=0.98±0.04 (<threshold), COR decreased, daily growth rate 1.25% / day (>1.2%, strategy maintained). Fixed flow rate group LD=1.18±0.10 (close to threshold), triggering flow rate cessation stimulation for 2 days.

[0096] Day 21: Inventive group LD=0.85±0.03 (<threshold), COR continues to decrease, daily growth rate 1.3% / day. Fixed flow rate group LD=1.28±0.03 (>threshold), triggering pause.

[0097] Table 8. Physiological and growth indicators of each group at different time points.

[0098] (c) Stable growth period (22-30 days): The average body length increases to 9.8 cm. Since the body length increase does not exceed 20 cm, the strategy requires maintaining the flow rate.

[0099] S5, Supporting Aquaculture Management Feeding: Feed daily at 7:00 AM when the flow rate is ≤0.6 BL / s. After feeding, reduce the flow rate to ≤0.5 BL / s within 30 minutes, and gradually increase it to the corresponding standard flow rate after 1 hour. Use floating pellets with a particle size of 0.3-1.0 mm. The daily feeding amount is 3-5% of the fish's body weight. Avoid feed loss. Clean excess food and residue from the tank before the flow rate increases. Change 40% of the aquaculture water every 2 days. While adjusting the flow rate, simultaneously maintain a water temperature of 28±1℃, dissolved oxygen ≥7.00 mg / L, and daily ammonia nitrogen ≤0.5 mg / L and nitrite <0.1 mg / L.

[0100] To verify the effectiveness of the method in Example 3, the growth of juvenile redfin snapper was measured after 30 days of culture: Control group: 15.5 ± 2.5 g; daily growth rate = 0.92% / day; Constant flow rate group: 17.7 ± 3.2 g; daily growth rate = 1.13% / day; Invention Group: 20.2 ± 3.8 g; Daily growth rate = 1.35% / day; The results show that the method of the present invention (staged flow rate regulation) significantly improves the growth rate and final weight of juvenile fish, and is an effective way to regulate the growth of juvenile redfin snapper.

[0101] This invention achieves low-stress, high-growth-efficiency aquaculture of juvenile red snapper by staged dynamic flow rate regulation combined with real-time monitoring and optimization of liver physiological indicators. In contrast, fixed flow rate regulation suffers from drawbacks such as frequent stress and poor growth continuity due to its single parameter and lack of dynamic adaptability. This invention further demonstrates the advanced nature and practicality of the method in the aquaculture of juvenile red snapper.

[0102] This invention illustrates a phased flow velocity regulation growth strategy for juvenile redfin snapper and proposes a method for improving the growth of juvenile redfin snapper by adjusting flow velocity. However, this invention is not limited to the described embodiment. Those skilled in the art can make equivalent modifications and substitutions for other body length groups, growth stages, fish species, and regulation cycles (such as stage duration, total regulation duration, and flow velocity change frequency) of the juveniles without departing from the spirit of this invention. All such equivalent modifications and substitutions are included within the scope defined by the claims of this application.

[0103] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0104] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for promoting the growth of juvenile redfin snapper by adjusting flow rate, characterized in that, Includes the following steps: S1. Determination of critical swimming speed: The absolute critical swimming speed Ua and relative critical swimming speed Ur of juvenile redfin snapper were determined by step speed test. The relative critical swimming speed Ur is the ratio of the absolute critical swimming speed Ua to the body length Bl. S2. Determine the maximum acclimatization speed VRM: Based on the relative critical swimming speed Ur measured in step S1, determine the limiting flow velocity value. Set multiple increasing flow velocity gradients within the range of 0 to the limiting flow velocity value to acclimatize juvenile fish. Observe and count the time juvenile fish remain still, move forward, and move backward at each flow velocity. Select the highest flow velocity where the forward movement time is greater than the backward movement time and set it as the maximum acclimatization speed VRM. S3. Phased Flow Rate Control: Throughout the entire rearing cycle, the water flow rate is dynamically adjusted in three phases to regulate the growth of juvenile redfin snapper, as detailed below: (a) Days 0-3, growth adaptation period: incremental variable flow stimulation was used. The initial flow rate was maintained at 0.5 Bl / s for 12 hours, and the rest of the time was kept still. Then, the flow rate was increased by 0.2 Bl / s each day until it reached 0.3 VRM. The flow rate was maintained for 12 hours each day, and the rest of the time was kept still. (b) Days 4-21, growth promotion period: periodic variable-speed water flow stimulation is used, specifically: From 8:00 to 12:00 daily, the flow rate is maintained at VRM; From 12:00 to 16:00 daily, the flow rate is reduced to 0.5 VRM; From 16:00 to 20:00 daily, the flow rate rebounded to 0.75 VRM; From 20:00 to 8:00 the next day, the flow rate is maintained at 0.25 VRM; (c) From day 22 to the end of the culture, during the stable growth period: constant water flow stimulation was used, and the flow rate was maintained at 0.5 VRM; when the body length of the juvenile fish was monitored to be more than 20% of the initial body length, the VRM value detection experiment was carried out again according to the new body length, and the S3 staged flow rate regulation was carried out again. S4. Dynamic optimization based on physiological indicators: During the aquaculture process, the liver glucose, lactic acid and cortisol content and daily growth rate of juvenile fish are monitored regularly, and the flow rate strategy is dynamically adjusted based on the monitoring results. S5. Supporting aquaculture management: Implement feeding and water quality management measures in conjunction with flow rate control.

2. The method according to claim 1, characterized in that, The method for determining the absolute critical swimming speed in step S1 is as follows: Multiple juvenile fish are placed in a flow rate of 0.5 BL / s for 30 min, and then the flow rate is increased by 0.5 BL / s every 30 min until the fish is exhausted. The fish is considered exhausted when it stays on the downstream honeycomb net for ≥20 s. The formula for calculating the absolute critical swimming speed Ua is: Ua = U + (ΔU * t / ΔT), where U is the highest speed of the fish during the entire time interval, ΔU is the speed increment, t is the sustainable swimming time of the fish at the highest flow rate, and ΔT is the specified time interval.

3. The method according to claim 1, characterized in that, In step S2, the limiting velocity value is equal to the relative critical swimming velocity.

4. The method according to claim 1, characterized in that, In step S2, "still" means that the fish remains in a fixed position and does not move with the water flow for more than 5 seconds; "moving forward" means that the fish actively swims forward against the current for a distance greater than 10cm; "moving backward" means that the fish is swept away by the water flow or actively moves backward with the current for a distance greater than 10cm.

5. The method according to claim 1, characterized in that, In step S4, the dynamic optimization based on physiological indicators specifically includes: Monitor the liver glucose, lactic acid, and cortisol levels, as well as the daily growth rate of the juvenile fish, every 7 days. When any of the following conditions are met, pause variable-speed stimulation and maintain the flow rate at 0.3 VRM until the indicators recover: Glucose content < 0.6 mmol / g protein; Lactic acid content > 1.2 mmol / g protein; Cortisol content > 30 ng / m² per gram of protein; Meanwhile, adjustments are made based on the daily growth rate: when the daily growth rate is ≥1.2% / day, the current flow rate strategy is maintained; when the daily growth rate is <1.2% / day, the current flow rate is increased by 0.1 Bl / s to stimulate the flow.

6. The method according to claim 5, characterized in that, The formula for calculating the daily growth rate is as follows: Daily growth rate = (W t W0) / (W0×t)×100%, where W t The average weight of the juvenile fish after rearing is in grams. W0 represents the average weight of the juvenile fish before rearing (in grams); t represents the number of days of rearing.

7. The method according to claim 1, characterized in that, In step S5, the supporting aquaculture management includes: Feed the fish daily when the flow rate is ≤0.3 VRM. Keep the flow rate ≤0.5 Bl / s for 30 minutes after feeding. Gradually increase the flow rate to the corresponding stage standard 1 hour after feeding. The daily feeding amount is 3%-5% of the fish's body weight. Use floating pellets with a particle size of 0.3-0.5mm and remove any uneaten feed before the flow rate increases. Replace 40% of the aquaculture water every 2 days; maintain water temperature at 28±1℃, dissolved oxygen ≥7.00 mg / L, and test ammonia nitrogen ≤0.5 mg / L and nitrite <0.1 mg / L daily.

8. The application of the method according to any one of claims 1-7 in promoting the growth of juvenile redfin snapper.

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