Method for improving egg carrying rate of scylla paramamosain under factory circulating water culture condition

Abstract

The invention discloses a breeding method of scylla paramamosain, and particularly relates to a method for improving the egg carrying rate of scylla paramamosain under the condition of factory circulating water culture, which comprises the following specific steps: 1) selecting mated female crabs with complete and healthy appendages, the weight of which is 400-500g, the gonad development reaches IV stage or above, and the ovary index is greater than 12%; (2) carrying out hot burning ablation on single-side eyestalks of the crab parents; and (3) controlling environmental parameters and strengthening baits during the breeding period of the crab parents. According to the method, the technical problem that the egg carrying rate is limited in artificial breeding of scylla paramamosain is effectively solved. According to the method for improving the egg carrying rate of the scylla paramamosain under the factory-like circulating water culture condition, the egg carrying rate of the scylla paramamosain can be remarkably improved through culture environment parameter setting, bait strengthening and single-side eyestalk ablation operation adopting a hot burning ablation method, namely, the reproductive capacity of the scylla paramamosain can be effectively promoted, and the survival rate of the scylla paramamosain is improved. Furthermore, the breeding efficiency of the scylla paramamosain is improved under the factory circulating water breeding condition.

Description

Technical Field

[0001] The invention relates to a breeding method for mud crabs, in particular to a method for improving the egg-carrying rate of mud crabs under factory-scale circulating water aquaculture conditions. Background Art

[0002] Scylla pseudoburrowing ( Scylla paramamosain Slush crabs, also known as mud crabs, belong to the genus Scylla, family Portunidae, order Decapoda, class Crustacea. They are widely distributed in the Yangtze River estuary and coastal waters to the south of my country. They are one of my country's most economically important marine fishery resources and marine aquaculture species. This species boasts rapid growth, delicious meat, and high nutritional value, and is in high demand in both domestic and international markets. According to the "2024 China Fisheries Statistical Yearbook," the mud crab cultivation area in 2023 was approximately 370,000 mu (approximately 16,000 hectares), with an annual production of 157,000 tons.

[0003] Despite the high production of blue crabs, numerous challenges remain in artificial breeding technology. For example, blue crab farming still relies on sea-caught seedlings, which not only results in unstable seed quality but also causes damage to natural resources due to overfishing. One of the main reasons for the blue crab industry's heavy reliance on wild seedlings is the shortage of high-quality parent crabs and the difficulty in cultivating brooding crabs. This leads to a shortage of artificial blue crab seedlings, a major bottleneck restricting the development of the blue crab industry.

[0004] Among them, the unsatisfactory egg-laying rate is one of the key factors restricting the development of the industry. In the natural environment, the mud crab is affected by the synergistic effect of various ecological conditions and can maintain a certain reproductive efficiency, but the artificial breeding environment is significantly different from the natural environment. On the one hand, the water quality of the aquaculture water body, such as key indicators such as temperature, salinity, and dissolved oxygen, is difficult to accurately simulate the seasonal changes and dynamic balance of the natural habitat. Temperatures that are too high or too low may interfere with the development of the female crab's gonads and disrupt its spawning cycle. On the other hand, during the gonadal development stage, the mud crab has strict requirements for nutrients such as protein and unsaturated fatty acids. If the nutrition of the bait is unbalanced and cannot meet its nutritional reserve needs, it will be difficult to increase the egg-laying rate.

[0005] In summary, given the bottleneck effect of the limited egg-carrying rate in artificial aquaculture of mud crabs on industrial development, there is an urgent need for a scientific and effective method to improve the current situation and increase the egg-carrying rate of mud crabs under factory-scale recirculating aquaculture conditions to ensure the sustainable development of the aquaculture industry.

[0006] Therefore, the applicant proposed the present invention. Summary of the Invention

[0007] The purpose of the present invention is to solve the above-mentioned deficiencies of the prior art and provide a method for improving the egg-carrying rate of mud crabs under factory-scale recirculating aquaculture conditions, which can effectively promote the reproductive capacity of mud crabs and thus improve the aquaculture efficiency of mud crabs under factory-scale recirculating aquaculture conditions.

[0008] To achieve the above objectives, the present invention provides a method for increasing the egg-carrying rate of mud crabs under industrial recirculating aquaculture conditions, which involves thermally ablating the unilateral eyestalk of the crab parent. Specifically, the method comprises the following steps: 1) Steps for selecting parent crabs Select healthy, mated female crabs with intact appendages, weighing 400-500 g, with gonadal development at stage IV or above and an ovarian index greater than 12%; 2) Hormone regulation steps of crab parents The unilateral eyestalk of the crab parent was thermally ablated; 3) Steps for promoting spawning of crab broodstock Crab parents with unilateral eyestalk ablation were cultured under a blue background; the culture area of ​​the crab parents was paved with fine sand with a thickness of 8-10 cm and a diameter of 3-5 mm; fresh or chilled shellfish were fed, with a daily feeding amount of not less than 5% of the crab parent's body weight, and adjusted according to feeding conditions; the water temperature was controlled at 25°C-30°C, the dissolved oxygen was above 6 mg / L, the salinity was 22.5±2.5ppt, the pH was 8.0±0.5, the ammonia nitrogen and nitrite concentrations were below 0.2 mg / L, the daily water exchange rate was 10%, and residual bait and feces were cleaned up irregularly according to water quality monitoring; a full-spectrum light source was used, the light intensity of the light source was 200Lx, and the daylight duration was 14h.

[0009] Furthermore, the above method for increasing the egg-carrying rate of mud crabs under factory-scale recirculating aquaculture conditions preferably includes: Temporary rearing steps for parent crabs After disinfection, the parent crabs were individually housed for 15 days. Fresh or chilled shellfish were fed starting on the fourth day of the temporary housing, and the feeding was adjusted according to feeding habits. The water temperature was controlled at 15-17°C, dissolved oxygen was above 6 mg / L, salinity was 25 ± 2 ppt, pH was 8.0 ± 0.5, ammonia nitrogen and nitrite concentrations were below 0.2 mg / L, and the water volume was changed by 10% daily. A full-spectrum light source was used, with a light intensity of 200 Lx and a daylight duration of 12 hours. The parent crabs with intact, healthy and vigorous appendages after temporary rearing are selected as crab parents and then subjected to unilateral eye stalk thermal ablation, and then to egg-promoting culture. The initial temperature of the egg-promoting culture is the same as that during the temporary rearing period, but the water temperature is increased at a rate of 1°C / day until it reaches 25°C-30°C.

[0010] In the above preferred technical solution, the parent crabs are further strictly screened to eliminate those with relatively poor vitality, so as to ensure excellent germplasm, stable genetic traits, good growth performance and disease resistance.

[0011] In addition, in the above-mentioned method for improving the egg-carrying rate of mud crabs under factory-scale recirculating aquaculture conditions, it is preferred to disinfect the parent crabs in 5 ppm potassium permanganate for 15 minutes and then in 2 ppm potassium persulfate for 30 minutes to complete the disinfection and reduce pathogen infection.

[0012] In addition, in the above method for improving the egg-carrying rate of mud crabs under factory-scale recirculating aquaculture conditions, feeding is preferably carried out between 19:00 and 20:00 every day during the temporary rearing and egg-carrying promotion cultivation period.

[0013] In addition, in the above-mentioned method of improving the egg-laying rate of mud crabs under factory-scale recirculating aquaculture conditions, the crab parents will have a certain stress response after the eyestalk is ablated, resulting in an inability to eat normally. Therefore, during the egg-laying induction cultivation period, it is preferred to start feeding fresh or chilled shellfish on the second or third day of cultivation to avoid unnecessary waste of bait.

[0014] The method of the present invention provides a method for improving the egg-carrying rate of mud crabs under factory-scale recirculating aquaculture conditions. The method can significantly improve the egg-carrying rate of mud crabs by setting aquaculture environment parameters, strengthening bait, and performing unilateral eyestalk ablation operation using a thermal ablation method. That is, the method can effectively promote the reproductive capacity of mud crabs, thereby improving the aquaculture efficiency of mud crabs under factory-scale recirculating aquaculture conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of the factory recirculating aquaculture system; Figure 2 This is a picture of the effect of unilateral eyestalk ablation using thermal ablation; Figure 3 are the survival rate (A) and egg-carrying rate (B) of the mud crab parents; Figure 4 The following are histological observations of the ovary of Scylla burrowing at 25°C water temperature (A1-A3); histological observations of the ovary of Scylla burrowing at 25°C water temperature and eyestalk ablation (B1-B3); histological observations of the ovary of Scylla burrowing at 30°C water temperature (C1-C3); histological observations of the ovary of Scylla burrowing at 30°C water temperature and eyestalk ablation (D1-D3); comparison of oocyte diameters in the ovarian tissue of Scylla burrowing (E); Figure 5 The contents of gonadal inhibitory hormone (GIH) (A), gonadotropin (GTH) (B), serotonin (5-HT) (C), and methyl farnesate (MF) (D) in the hemolymph of the parent mud crab. DETAILED DESCRIPTION

[0016] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention are within the scope of protection of the present invention. Example 1:

[0017] The method provided in this embodiment for increasing the egg-carrying rate of mud crabs under factory-scale recirculating aquaculture conditions includes the following specific steps: Parent crab selection: The quality of the parent crabs determines the quality of the subsequent brooding crabs and their offspring. Therefore, select parent crabs that are vigorous, have healthy appendages, are free of external injuries and carapace ulcers, and have well-developed ovaries. They should weigh between 400-500 g, have a total carapace width of approximately 13 cm, and have gonadal development at or above stage IV, with an ovarian index greater than 12%.

[0018] Temporary rearing of parent crabs: Disinfect parent crabs in 5 ppm potassium permanganate for 15 minutes, then in 2 ppm potassium persulfate for 30 minutes. After disinfection, place the parent crabs in a "crab apartment" for temporary rearing. The "crab apartment" consists of several culture units (length * width * height = 45 cm * 30 cm * 20 cm), with one crab placed in each culture unit for individual rearing. No feeding is performed during the first three days of temporary rearing, and crabs that die due to transportation or stress are eliminated. After the fourth day, fresh Manila clams are fed daily from 7:00 PM to 8:00 PM, and the feeding amount for the next day is adjusted based on the previous day's feeding habits. Temporary rearing lasts for a total of 15 days. During this period, the water temperature is controlled at 15-17°C, salinity at 23-27 ppt, dissolved oxygen (DO) > 6 mg / L, pH at 8.0 ± 0.5, and total ammonia nitrogen (TAN) and NO2 - -N < 0.2 mg / L, a full-spectrum light source was used, the light intensity of the light source was 200 Lx, the photoperiod was 12L:12D (photophase was 6:00-18:00), the light intensity was 200 lx, and 10% of the seawater was replaced every day in the "Crab Apartment" system.

[0019] Preparation of facilities for crab broodstock (egg-bearing crabs): Prepare a factory-scale recirculating aquaculture system in advance. Figure 1As shown, the system comprises a water treatment system and aquaculture equipment. The water treatment system includes a microfiltration unit, a protein skimmer, a biofilter, an aeration pump, and a UV sterilizer. The aquaculture equipment includes aquaculture tanks and a water quality monitoring system. An 8 mm thick transparent acrylic partition, pre-punched with several holes to facilitate water exchange, is placed between each aquaculture tank. Once the partition is in place, each aquaculture tank is divided into two independent aquaculture spaces. At the bottom of each aquaculture space is a blue frame (length * width * height = 40 cm * 30 cm * 15 cm) filled with fine sand. The sand layer is 8 cm to 10 cm thick and 3 to 5 mm in diameter. This sand layer provides a substrate for the eggs of the mud crabs.

[0020] Hormone regulation of crab parents: Select healthy and vigorous crabs with sound appendages and mature ovaries from the temporarily reared parent crabs and transfer them to the above-prepared breeding system. Place a mud crab on each side of each breeding bucket, that is, each system contains 24 mud crabs. The initial temperature of the system is the same as that during the temporary rearing period (15℃-17℃). After the crabs are settled, the water temperature is increased at a rate of 1℃ / day until it reaches 25℃. Subsequently, all mud crab individuals are uniformly subjected to unilateral eye stalk heat cauterization and ablation. In this embodiment, the left eye stalk is subjected to heat cauterization and ablation. Before the operation, use alcohol cotton balls or iodine tincture to wipe and disinfect the eye stalk and the surrounding area to reduce the risk of postoperative infection. During the operation, use sterile tweezers that have been heated red by an alcohol lamp to achieve the heat cauterization effect and minimize the risk of infection. Using the heat cauterization and ablation method, the red-hot tweezers are used to clamp the base of the unilateral eye stalk for a few seconds to burn it at high temperature, thereby destroying the X-organ-sinus gland complex in the eye stalk, such as Figure 2 As shown, this interferes with hormone secretion. It is worth noting that burning only the base of the eyestalk, rather than directly removing it, reduces individual stress and injury, improving survival rates and operational safety. This is particularly suitable for improving the aquaculture efficiency of mud crabs under factory-scale recirculating aquaculture conditions, where the goal is to reduce mortality.

[0021] Crab broodstock incubation: Broodstock crabs experience a certain stress response immediately after eyestalk ablation. Therefore, do not feed them for 1-2 days to avoid unnecessary food waste. Once the crabs have stabilized, feed them clams or razor clams daily between 7:00 PM and 8:00 PM, approximately 5% of their body weight. Adjust the amount the following day based on feeding activity. Carefully remove any remaining bait and feces daily to prevent deterioration of the sand and water quality. During the brooding period, water quality should also be monitored and controlled. The water temperature should be maintained at 25°C, dissolved oxygen above 6 mg / L, salinity at 20-25‰, pH at 8.0 ± 0.5, and ammonia nitrogen and nitrite concentrations below 0.2 mg / L. The light cycle should be adjusted from the 12 L:12 D cycle used during the initial aquarium to 14 L:10 D, with lights on at 5:00 AM and off at 7:00 PM. Patrols were conducted several times every morning, noon and evening to observe the survival and egg-laying status of blue crabs. Water was changed at 14:00 in the afternoon, with a water change rate of 10% per day. Example 2:

[0022] The present embodiment provides a method for increasing the egg-carrying rate of mud crabs under factory-scale recirculating aquaculture conditions. The specific steps are consistent with those of the above embodiment, except that the water temperature is controlled at 30° C. during the egg-carrying incubation stage of the crab parents.

[0023] Comparative Example 1: This comparative example provides a method for improving the egg-carrying rate of mud crabs under factory-scale recirculating aquaculture conditions. The specific steps are consistent with the aforementioned embodiment. However, in this comparative example, unilateral eyestalk thermal ablation treatment is not uniformly performed on all mud crab individuals, and the water temperature of the crab parents is controlled at 25°C during the egg-carrying incubation stage.

[0024] Comparative Example 2: The only difference between this comparative example and the aforementioned comparative example is that the water temperature during the brooding stage of the crab broodstock is controlled at 30°C.

[0025] The results showed that the survival rate of mud crabs did not change whether the eyestalk was ablated or not. The survival rate of mud crabs in each case was stable at around 80% (e.g. Figure 3 The egg-carrying rates of mud crabs without eyestalk ablation (Comparative Examples 1 and 2) at 25°C and 30°C were 12.2 ± 10.7% and 17.0 ± 2.9%, respectively, while the egg-carrying rates of mud crabs with eyestalk ablation (Examples 1 and 2) at 25°C and 30°C were 41.1 ± 8.4% and 50.0 ± 10.0%, respectively, indicating that unilateral eyestalk ablation can significantly increase the egg-carrying rate of mud crabs (as shown in Figure 2). Figure 3 B).

[0026] In addition, in each of the above examples, individual samples of mud crabs were collected and their biological characteristics were observed and tested. Specifically: Histological observations showed that the ovarian tissue of the mud crab had complete and clearly structured oocytes (Oc), in which yolk granules (Yg) were evenly distributed within the oocytes ( Figure 4 A1-D3). In addition, clear nuclei (Nu) and nucleoli (No) structures were observed, indicating that the oocytes were in the early stage of maturation (stage IV) as defined by the gonadal index (GSI). To further investigate the status and development of oocytes, the diameter of oocytes ( Figure 4 E). The results showed that eyestalk ablation significantly increased the diameter of oocytes. At 30°C, the diameter of oocytes from blue crabs treated with eyestalk ablation was significantly larger than that from blue crabs without eyestalk ablation.

[0027] Through the detection of hormone content in the hemolymph of blue crabs, it was found that the content of gonad-inhibiting hormone (GIH) in the hemolymph of blue crabs decreased significantly after the eyestalk was ablated at 25℃ and 30℃ (such as Figure 5 At the same time, eyestalk ablation at 30°C significantly increased the level of gonadotropin (GTH) (as shown in Figure 2A). Figure 5 In addition, there was no significant difference in the expression of 5-hydroxytryptamine (5-HT) and methylfarnesate (MF) (Fig. Figure 5 C and D). Thus, unilateral eyestalk ablation further enhances the egg-laying rate by reducing the level of gonadal inhibitory hormone and increasing the level of gonadotropin in the hemolymph of S. pseudoburrows.

[0028] The present invention is not limited to the above-mentioned optimal implementation mode. Anyone can derive other forms of products under the inspiration of the present invention. However, no matter what changes are made in the shape or structure, any technical solution that is the same or similar to that of the present application falls within the scope of protection of the present invention.

Claims

1. A method for increasing the egg-carrying rate of mud crabs under factory-scale recirculating aquaculture conditions, characterized by: The unilateral eyestalk of the crab parent was thermally ablated.

2. The method for increasing the egg-carrying rate of mud crabs under industrial circulating aquaculture conditions according to claim 1, characterized in that The specific steps include the following: 1) Steps for selecting parent crabs Select healthy, mated female crabs with intact appendages, weighing 400-500 g, with gonadal development at stage IV or above and an ovarian index greater than 12%; 2) Hormone regulation steps of crab parents The unilateral eyestalk of the crab parent was thermally ablated; 3) Steps for promoting spawning of crab broodstock Crab parents with unilateral eyestalk ablation were cultured under a blue background; the culture area of ​​the crab parents was paved with fine sand with a thickness of 8-10 cm and a diameter of 3-5 mm; fresh or chilled shellfish were fed, with a daily feeding amount of not less than 5% of the crab parent's body weight, and adjusted according to feeding conditions; the water temperature was controlled at 25°C-30°C, the dissolved oxygen was above 6 mg / L, the salinity was 22.5 ±2.5ppt, the pH was 8.0 ± 0.5, the ammonia nitrogen and nitrite concentrations were below 0.2 mg / L, the daily water exchange rate was 10%, and residual bait and feces were cleaned up irregularly according to water quality monitoring; a full-spectrum light source was used, the light intensity of the light source was 200Lx, and the daylight duration was 14h.

3. The method for increasing the egg-carrying rate of mud crabs under factory-scale circulating aquaculture conditions according to claim 2, characterized in that Also includes: Temporary rearing steps for parent crabs After disinfection, the parent crabs were individually housed for 15 days. Fresh or chilled shellfish were fed starting on the fourth day of the temporary housing, and the feeding was adjusted according to feeding habits. The water temperature was controlled at 15-17°C, dissolved oxygen was above 6 mg / L, salinity was 25 ± 2 ppt, pH was 8.0 ± 0.5, ammonia nitrogen and nitrite concentrations were below 0.2 mg / L, and the water volume was changed by 10% daily. A full-spectrum light source was used, with a light intensity of 200 Lx and a daylight duration of 12 hours. The parent crabs with intact, healthy and vigorous appendages after temporary rearing are selected as crab parents and then subjected to unilateral eye stalk thermal ablation, and then to egg-promoting culture. The initial temperature of the egg-promoting culture is the same as that during the temporary rearing period, but the water temperature is increased at a rate of 1°C / day until it reaches 25°C-30°C.

4. The method for increasing the egg-carrying rate of mud crabs under industrial recirculating aquaculture conditions according to claim 3, characterized in that: The parent crabs were disinfected in 5 ppm potassium permanganate for 15 minutes and then in 2 ppm potassium persulfate for 30 minutes to complete the disinfection.

5. The method for increasing the egg-carrying rate of mud crabs under industrial recirculating aquaculture conditions according to claim 3, characterized in that: During the period of temporary rearing and egg incubation, feeding is carried out between 19:00 and 20:00 every day.

6. The method for increasing the egg-carrying rate of mud crabs under industrial recirculating aquaculture conditions according to claim 1, 2, 3, 4, or 5, characterized in that: During the egg-incubation period, start feeding fresh or chilled shellfish on the second or third day of cultivation.

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