Group breeding method of blue crab fast-growing strain

Abstract

The invention provides a blue crab fast-growing strain group breeding method, and aims to improve the growth speed and quality of blue crabs through multi-generation continuous breeding. The method comprises the following steps: firstly, breeding offspring seeds of a basic group, carrying out high-intensity screening in different growth stages, and selecting individuals which grow fastest for breeding; carrying out third screening before reproductive shelling, and selecting male crabs and female crabs which grow fastest; then carrying out free mating and overwintering; the female crabs are screened for the last time in spring, and it is ensured that the selected female crabs are healthy and free of diseases; and finally carrying out egg carrying, membrane rupture incubation and cultivation to form a breeding group. In the breeding process, a far-source population is introduced for germplasm rejuvenation, and a microsatellite (SSR) molecular marker is used for genetic diversity and heritability evaluation. In addition, the method further comprises the steps that specific bait feeding is conducted on the blue crabs in different growth stages, and the breeding environment is strictly controlled. Through the steps, the growth performance and genetic quality of the blue crabs can be effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of blue crab breeding, and more specifically to a method for breeding a blue crab fast-growing strain population. Background Art

[0002] Blue crabs are large, fast-growing, and delicious, making them an excellent marine aquaculture crab. Blue crab farming has the advantages of low investment, quick results, good benefits, and convenient technical management, and has become an emerging marine industry. Blue crab farming technology has made continuous breakthroughs, and the farming area has increased, but the per-acre yield is generally not high, which limits the further development of the industry. The increase in farming output needs to rely on the improvement of breeding of fine varieties.

[0003] The seed industry is at the forefront of the agricultural industry chain and is a core element that determines the development of modern agriculture and social stability. The aquatic seed industry is the main component of the seed industry. It is the foundation for ensuring the safe and effective supply of aquatic products and promoting the healthy and sustainable development of the modern aquatic industry. It is also the hard-core "chip" for promoting the transformation and upgrading of fisheries and realizing the modernization of fisheries. At present, the blue crab farming industry is facing many problems and challenges, which poses a serious threat to the sustainable and healthy development of the entire industry. First, blue crab seedlings mainly rely on fishing in the sea area. Wild seedlings have uneven quality and large individual differences. The lack of quarantine makes them easy to carry a large number of pathogens and seedlings from different regions are mixed. Second, repeated outbreaks of diseases often occur during breeding. Therefore, further strengthening the research on the selection and breeding of blue crab varieties, exploring new breeding models, and implementing effective disease prevention and control measures are the key to promoting the sustainable and healthy development of China's blue crab industry. Summary of the invention

[0004] In view of the shortcomings of the existing technology, the present invention provides a method for breeding a group of fast-growing blue crab strains, and carries out breeding and genetic improvement of blue crabs to improve breeding efficiency and industrial competitiveness. The breeding method adopts a breeding method combining group breeding and molecular marker-assisted selection to carry out breeding of fast-growing new strains, and at the same time integrates and improves large-scale breeding technology to promote the industrial application of blue crabs.

[0005] To achieve the above object, the present invention provides the following technical solution: a method for breeding a fast-growing strain of blue crab, comprising the following steps:

[0006] A. Cultivate the progeny seedlings of the basic population to the fifth stage, intensively screen 20% of the individuals, and culture the screened individuals in pond enclosures;

[0007] B. When the crabs weigh 20-30g, secondary screening is carried out, and 20% of the male and female crabs are screened separately, and the selected individuals are moved into small ponds for breeding;

[0008] C. After the first molt before reproductive molt is completed in a small pond, the crab seedlings are caught and subjected to a third intensive screening according to male and female crabs, and the top 20% are screened to obtain the fastest growing male and female crabs;

[0009] D. After the last reproductive molt is completed, free mating is carried out;

[0010] E. After mating, the female crabs will hibernate and be picked out in spring for the final screening to obtain female crabs without any injuries or diseases on their body surface;

[0011] F. After the female crabs hold the eggs, break the membranes to hatch and cultivate them, the offspring breeding group is obtained;

[0012] G. Repeat steps AF for multiple generations of continuous breeding.

[0013] The present invention is further configured as follows: the seedlings are selected from more than 5 wild geographical groups of blue crabs with roe crabs, with reference to biological indicators such as the weight, carapace width, and gonad development of blue crabs. More than 50 roe crabs are selected from each group, and the negative groups are left after independent breeding, sampling, and virus PCR testing to evaluate the genetic diversity of the germplasm resources of the groups and the relationship between the groups. Then, based on the standards of strong physique, complete appendages, and good gonad development, 50% pressure selection is carried out to establish a basic group of more than 100 blue crab fast-growing strains, and the crab seedlings obtained from the roe crab group within 3-5 days after the eggs are broken are regarded as the same batch of crab seedlings.

[0014] The present invention is further configured as follows: in the step E, it also includes a step E1 of introducing a distant source population in each generation to rejuvenate the population germplasm:

[0015] E1. Select crabs weighing more than 500 g, with good body color, strong vitality, and no diseases or injuries in the sea area or outside ponds, introduce them as foreign species, and mix them with the female crabs screened in step E, with the mixing ratio of 30-50%.

[0016] The present invention is further configured to include: using microsatellite (SSR) molecular markers to evaluate the genetic diversity and heritability of the core population of generations, so as to provide guidance for population management and protection strategies.

[0017] The present invention is further configured as follows: the seedlings in step A are selected from large-eyed larvae with strong vitality and good phototropism.

[0018] The present invention is further configured as follows: the criteria for the enhanced screening include but are not limited to ranking by physique, complete limbs and weight, and the top 20% of the individuals are selected as the enhanced screening of 20%.

[0019] The present invention is further configured as follows: in step E, the overwintering cultivation conditions of blue crabs are: fine sand is spread on the bottom of the pond, plastic frames made of PE material are arranged in the pond, the frame openings are tied with large-mesh nylon nets, the bottom of the plastic frames are fixed to the bottom of the pond, and the average thickness of the fine sand in the frames is more than 10 cm; clams, clams and other shellfish are fed regularly and quantitatively every day, and more than 30% of disinfected seawater is added and replaced the next day, and the residual bait in the frames is removed and the bait is replenished. The overwintering crabs are moved to the pond once every 15 days, and the old pond is cleaned of bait and then the sand is washed and cleaned, and thoroughly disinfected with bleaching powder.

[0020] The present invention is further configured as follows: in the crab seedling stage of step A, the bait is mainly fed with Artemia and krill; in the stage of step B, the bait is mainly fed with clams, supplemented with blue clams; in the stage of step CE, the bait is mainly fed with low-value shellfish and wild fish; in the stage of step AE, the bait is fed in sufficient amount.

[0021] The present invention is further configured as follows: in step C and step D, the reproductive molting refers to the last molting performed by the female crab when it reaches sexual maturity for the purpose of reproduction and mating.

[0022] The present invention is further configured to include seedling data statistics: selecting a core breeding area for blue crabs, establishing a breeding group and a wild control group in the breeding area, the breeding ponds and feeding management of the two groups are consistent, and after being cultivated into crab roe, including but not limited to using body weight, survival rate, carapace width, and carapace length as measurement indicators, obtaining specific weight gain rate, absolute weight gain rate, and coefficient of variation data of body length and weight traits of the breeding group and the wild control group, providing basic data for the estimation of genetic parameters of growth traits.

[0023] In summary, the present invention has the following beneficial effects:

[0024] The invention carries out three times of enhanced screening at different stages of blue crabs, and through the enhanced screening at different stages, blue crabs with fast growth and development and excellent traits at different stages are selected, and blue crab varieties with fast growth and excellent traits are selected through multi-generation group breeding;

[0025] The present invention uses microsatellite (SSR) molecular markers to evaluate the genetic diversity and heritability of the core population of generations, introduces foreign distant population species into the generations to carry out germplasm rejuvenation, enrich the gene pool, ensure genetic diversity, prevent degeneration after multiple generations of breeding, and avoid inbreeding and genetic decline.

[0026] The present invention conducts seedling data statistics, and obtains the improvement ratio and variation coefficient of corresponding traits by testing and comparing with local wild seedlings in the core breeding area of ​​blue crab, thereby providing basic data for the genetic parameters of growth shape, thereby understanding the effect of breeding improvement after multiple generations of breeding, and more accurately judging the changes in genetic traits after multiple generations of breeding, which is convenient for carrying out large-scale breeding technology.

[0027] The method of the invention is simple to operate, the breeding stage settings are reasonable, the breeding effect is good, and the breeding benefits are effectively promoted. DETAILED DESCRIPTION

[0028] The present invention is described in further detail below.

[0029] This embodiment discloses a method for breeding a fast-growing strain of blue crab, comprising the following steps:

[0030] A. Cultivate the progeny seedlings of the basic group to the fifth stage of crab larvae, intensively screen 20% of the individuals, and culture the screened individuals in pond enclosures; by conducting early screening at the crab larvae stage, individuals with rapid growth potential can be identified and cultivated as early as possible, which helps to improve the overall breeding efficiency and speed up the overall breeding efficiency.

[0031] B. When the crabs weigh 20-30g, they are screened for the second time, and 20% of the individuals are screened for male and female crabs respectively. After screening, they are moved to small ponds for breeding; small ponds can provide an environment more suitable for the current growth needs of blue crabs, thereby optimizing growth conditions and facilitating management. Male and female crabs are screened separately, because male crabs grow slightly faster than female crabs at this time. If they are not distinguished, too many male crabs will be screened out. Therefore, distinguishing between male and female can ensure that the best individuals of both sexes can be selected, which helps to improve the breeding effect and the quality of the offspring.

[0032] C. After the crabs are cultured in a small pond until the last molt before the reproductive molt is completed, the crabs are caught and subjected to a third intensive screening for male and female crabs, respectively, to select the top 20% and obtain the fastest growing male and female crabs; the screening before the reproductive molt helps to ensure that the selected individuals have shown excellent growth traits before reproduction, which is particularly important for genetic improvement. At the same time, through multiple screenings in the above steps AC, through multiple intensive screenings, the screening is gradually improved, which can ensure that the selected individuals are the fastest growing in each stage, thereby gradually improving the overall growth rate of the group.

[0033] D. After the last reproductive molt is completed, free mating is allowed. Free mating can also allow stronger male crabs to have better breeding opportunities to a certain extent, and also help to obtain a better population of blue crabs.

[0034] E. After mating, the female crabs hibernate and are picked out in the spring for a final screening to obtain female crabs without injuries or diseases on their body surface. Health screening of female crabs before they lay eggs can ensure that the breeding female crabs are free of injuries and diseases, thereby increasing the hatching rate and survival rate of the larvae.

[0035] F. After the female crabs hold the eggs, break the membranes to hatch and cultivate them, the offspring breeding group is obtained;

[0036] G. Repeat steps AF to carry out continuous breeding for multiple generations. Through continuous breeding for multiple generations, excellent traits can be gradually accumulated to form a genetically stable improved population.

[0037] Table 1 compares the growth rates of wild strains and selected strains;

[0038] Group Initial weight (g) Final weight (g) Specific growth rate (% / d) Wild juvenile crabs 3.41±0.21 311.67±15.82 2.51±0.01 Selecting young crabs 3.46±0.24 384.65±17.03 2.62±0.02

[0039] Table 2 shows the comparison of survival rates between wild strains and selected strains;

[0040] Group Survival rate Wild juvenile crabs 10.5％ Selecting young crabs 16.2％

[0041] Table 3 is a comparison of per-acre yields of wild strains and selected strains

[0042] Group Yield per mu Wild juvenile crabs 75kg Selecting young crabs 129kg

[0043] It can be seen that after group selection, the growth rate, survival rate and yield have been significantly improved.

[0044] Furthermore, the seedlings are selected from more than 5 wild geographical groups of blue crabs with roe crabs, with reference to biological indicators such as weight, carapace width, and gonad development. More than 50 roe crabs are selected from each group, and the negative groups are left after independent breeding, sampling, and virus PCR testing to evaluate the genetic diversity of the germplasm resources of the groups and the relationship between the groups. Then, based on the standards of strong physique, complete appendages, and good gonad development, 50% pressure selection is carried out to establish a basic group of more than 100 blue crab fast-growing strains for breeding. The crab seedlings obtained from the roe crab group within 3-5 days after the eggs are broken are regarded as the same batch of crab seedlings. By selecting individuals with strong physique, complete appendages and well-developed gonads, the high quality of germplasm resources is ensured, laying a good foundation for subsequent breeding work. Through pressure selection, individuals with excellent traits can be screened out to provide support for establishing a basic population for breeding of fast-growing strains. Selecting crab seedlings that break the membrane within 3-5 days as seedlings from the same batch helps to ensure the homogeneity of the seedlings and ensure that the growth and development stages of the seedlings are consistent, thereby making fair comparisons in subsequent screening.

[0045] In step E, it also includes step E1 of introducing distant source populations to rejuvenate the population germplasm in each generation:

[0046] E1. Select crabs weighing more than 500g, with good body color, strong vitality, and no diseases or injuries in the sea area or outside ponds, introduce them as foreign species, and mix them with the female crabs screened in step E, with a mixing ratio of 30-50%. Introducing foreign species can increase the diversity of the gene pool, prevent genetic degeneration caused by inbreeding, and improve the adaptability and survival ability of the offspring.

[0047] Furthermore, it also includes the use of microsatellite (SSR) molecular markers to evaluate the genetic diversity and heritability of the core population of generations, which is used to provide guidance for population management and conservation strategies, and to ensure that the breeding core population has rich genetic diversity, high heterozygosity and long genetic distance.

[0048] Furthermore, the seedlings in step A are selected from large-eyed juveniles with strong vitality and good phototropism. By screening the seedlings in advance, it is helpful to select potential individuals and speed up the overall breeding speed.

[0049] Furthermore, the criteria for the enhanced screening include but are not limited to ranking by physique, complete appendages and weight, and the top 20% of individuals are selected as the enhanced screening 20%. Through quantitative screening with specific criteria, statistical screening can be better performed. At the same time, on this basis, those skilled in the art can further refine the criteria and perform targeted breeding.

[0050] In step E, the wintering cultivation conditions of blue crabs are as follows: fine sand is spread on the bottom of the pond, plastic frames made of PE material are arranged in the pond, the mouth of the frame is tied with a large-mesh nylon mesh, the bottom of the plastic frame is fixed to the bottom of the pond, and the average thickness of the fine sand in the frame is more than 10 cm; razor clams, clams and other shellfish are fed regularly and quantitatively every day, and more than 30% of disinfected seawater is added and replaced the next day, and the residual bait in the frame is removed and the bait is replenished. The wintering crabs are moved to the pond once every 15 days. After cleaning the bait in the old pond, the sand is flushed and washed, and it is thoroughly disinfected with bleaching powder. The wintering period is generally more than 3 months. The crabs' cannibalistic characteristics lead to a low wintering survival rate. After adopting the above conditions, the shelters set at the bottom of the pond can simulate the natural environment and control the number of blue crabs in a unit space. The fine sand provides the blue crabs with sand-lying conditions, while increasing the stability of the plastic frame, and the bottom sand layer can regulate the temperature to a certain extent, thereby improving the wintering survival rate. In addition, feeding bait at regular intervals and in fixed quantities can also reduce the rate of mutual cannibalism; the water quality should be changed daily and leftover bait should be removed to reduce the growth of pathogens and harmful microorganisms and maintain the hygiene of the breeding environment.

[0051] In the crab seedling stage of step A, the bait is mainly Artemia and krill; in the stage of step B, the bait is mainly clams, supplemented by blue clams; in the stage of step CE, the bait is mainly low-value shellfish and wild fish; in the stage of step AE, the bait is fed in sufficient amount. Through the above steps, different baits are fed at different growth stages, and the targeted feeding strategy helps to meet the nutritional needs of blue crabs at different growth stages and promote their healthy growth. At the same time, sufficient feeding at the corresponding stage ensures that the blue crabs can obtain sufficient nutrition and improve the overall growth efficiency and survival rate.

[0052] In step C and step D, the reproductive molt refers to the last molt performed by the female crab when the female crab is sexually mature and for reproduction and mating. Before the reproductive molt, the male crab will wait beside the female crab, and after the molt is completed and the crab shell becomes soft, mating will be performed. Therefore, step C must be screened after the molt before the reproductive molt is completed. Screening cannot be performed in the early stage of the reproductive molt due to the habits of male and female crabs.

[0053] Furthermore, the present invention also includes seedling data statistics: select the core breeding area of ​​blue crab, establish a breeding group and a wild control group in the breeding area, the breeding ponds and feeding management of the two groups are consistent, and after being cultivated into crab roe, including but not limited to weight, survival rate, cephalothorax width, and cephalothorax length as measurement indicators, obtain the specific weight gain rate, absolute weight gain rate, and coefficient of variation data of body length and weight traits of the breeding group and the wild control group, and provide basic data for the estimation of genetic parameters of growth traits. Through the statistics of control data of breeding and wild seedlings, the trait changes of seedlings after breeding are scientifically recorded, and the collected data provide a basis for the estimation of genetic parameters of growth traits, which is helpful for more in-depth genetic research and the formulation of breeding strategies, especially after multiple generations of breeding, the trait change rate of each generation can also be evaluated, and the trait changes between each generation can be further tracked. The trait changes between each generation are timely discovered, and the economic benefits between breeding and breeding are evaluated, providing a reference for future population breeding.

[0054] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the design concept of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for breeding a fast-growing strain of blue crab, characterized in that: The following steps are involved: A. Cultivate the progeny seedlings of the basic population to the fifth stage, intensively screen 20% of the individuals, and culture the screened individuals in pond enclosures; B. When the crabs weigh 20-30g, secondary screening is carried out, and 20% of the male and female crabs are screened separately, and the selected individuals are moved into small ponds for breeding; C. Cultivate the crabs in a small pond until the last molt before the reproductive molt is completed, catch the crabs, and conduct a third intensive screening of male and female crabs respectively, and select the top 20%, and obtain the fastest growing male and female crabs; D. After the last reproductive molt is completed, free mating is carried out; E. After mating, the female crabs will hibernate and be picked out in spring for the final screening to obtain female crabs without any injuries or diseases on their body surface; F. After the female crabs hold the eggs, break the membranes to hatch and cultivate them, the offspring breeding group is obtained; G. Repeat steps AF for multiple generations of continuous breeding.

2. The method for breeding a fast-growing strain of blue crab according to claim 1, characterized in that: The described seedlings are selected from more than 5 wild geographical groups of blue crab roe with reference to biological indicators such as blue crab weight, cephalothorax width, gonad development, etc., and more than 50 blue crab roe crabs are retained in each group. After independent breeding, sampling, and virus PCR detection, negative groups are retained to evaluate the genetic diversity of group germplasm resources and the relationship between groups. Then, based on the standards of strong physique, complete appendages, and good gonad development, 50% pressure selection is carried out to establish a basic group of blue crab fast-growing strains with more than 100 blue crabs. The crab seedlings obtained from the roe crab group within 3-5 days after ovum breaking are regarded as crab seedlings from the same batch.

3. The method for breeding a fast-growing strain of blue crab according to claim 1, characterized in that: In the step E, it also includes the step E1 of introducing distant source populations in each generation to rejuvenate the population germplasm: E1. Select crabs with a size of more than 500g, good body color, strong vitality, and no disease or injury in the sea area or outside ponds, introduce them as foreign species, and mix them with the female crabs selected in step E. The mixing ratio is 30-50％。 4. The method for breeding a fast-growing strain of blue crab according to claim 1, characterized in that: It also includes the use of microsatellite (SSR) molecular markers to assess genetic diversity and heritability of generational core populations to provide guidance for population management and conservation strategies.

5. The method for breeding a fast-growing strain of blue crab according to claim 1, characterized in that: The seedlings in step A are selected from large-eyed larvae with strong vitality and good phototropism.

6. The method for breeding a fast-growing strain of blue crab according to claim 1, characterized in that: The criteria for the enhanced screening include, but are not limited to, ranking by physique, complete limbs and weight, and the top 20% of individuals are selected as the enhanced screening 20%.

7. The method for breeding a fast-growing strain of blue crab according to claim 1, characterized in that: In step E, the overwintering culture conditions of blue crabs are as follows: fine sand is spread on the bottom of the pond, plastic frames made of PE material are arranged in the pond, the frame openings are tied with large-mesh nylon meshes, the bottoms of the plastic frames are fixed to the bottom of the pond, and the average thickness of the fine sand in the frames is more than 10 cm; clams, clams and other shellfish are fed regularly and quantitatively every day, more than 30% of disinfected seawater is added and replaced the next day, residual bait in the frames is removed, and bait is replenished; the overwintering crabs are moved to the pond once every 15 days, the old pond is cleaned of bait, the sand is flushed and washed, and the pond is thoroughly disinfected with bleaching powder.

8. The method for breeding a fast-growing strain of blue crab according to claim 1, characterized in that: In the crab seedling stage of step A, the bait is mainly Artemia and krill; in the stage of step B, the bait is mainly clams, supplemented by blue clams; in the stage of step CE, the bait is mainly low-value shellfish and wild fish; in the stage of step AE, the bait is fed in sufficient amount.

9. The method for breeding a fast-growing strain of blue crab according to claim 1, characterized in that: In step C and step D, the reproductive molting refers to the last molting performed by the female crab when it reaches sexual maturity for reproduction and mating.

10. The method for breeding a fast-growing strain of blue crab according to claim 1, characterized in that: It also includes seedling data statistics: select the core breeding area for blue crabs, establish a breeding group and a wild control group in the breeding area, and the breeding ponds and feeding management of the two groups are consistent. After they are cultivated into roe crabs, including but not limited to weight, survival rate, carapace width, and carapace length as measurement indicators, obtain the specific weight gain rate, absolute weight gain rate, and coefficient of variation data of body length and weight traits of the breeding group and the wild control group, providing basic data for the estimation of genetic parameters of growth traits.