Cultivation method of a new triploid strain of Crassostrea hongkongensis with high salt tolerance and fast growth

Abstract

The invention discloses a cultivation method for a new triploid strain of Crassostrea hongkongensis with high salt tolerance and fast growth. Through technical links such as screening of diploid populations with high salt tolerance, breeding of new diploid strains with high salt tolerance and fast growth, establishment of tetraploid induction lines with high salt tolerance and fast growth, breeding of new tetraploid strains with high salt tolerance and fast growth, and production of new triploid strains with high salt tolerance and fast growth, and by combining stress selection breeding technology and polyploid breeding technology, a new triploid strain of Crassostrea hongkongensis with high salt tolerance, poor fertility, fast growth, high quality and marketable throughout the year is cultivated, which can effectively solve the industrial problem of high mortality of diploid Crassostrea hongkongensis in some places, and has great potential and value for popularization and application.

Description

Technical Field

[0001] The present invention belongs to the technical field of shellfish genetic breeding in marine agriculture, and specifically relates to a method for cultivating a new triploid strain of Crassostrea hongkongensis that is highly salt-tolerant and grows fast. Background Art

[0002] Crassostrea hongkongensis, commonly known as white oyster, is mainly cultivated and distributed in the estuary and sea area. It is an important shellfish economic species in South China. The output in 2022 was about 1.85 million tons, accounting for about 29.86% of the national oyster output. It can be said that it has important economic value. Crassostrea hongkongensis has the advantages of thick shell, white meat, strong umami taste, rich nutritional value, and tough and elastic meat, and is widely loved by consumers in South China. The market selling price has soared all the way and is in short supply. It has increased from about 4 yuan per catty in 2014 to about 10 yuan per catty in 2023. The upstream and downstream industrial chains such as cultivation, sales, processing, and catering have been continuously expanding and the industry has been continuously upgraded. The Crassostrea hongkongensis industry is even a pillar industry in some coastal towns of Guangdong and Guangxi.

[0003] The traditional cultivation of Crassostrea hongkongensis needs to be migrated in combination with the change of sea area salinity. Generally, in December of each year, the oyster rafts need to be migrated to the estuary area with lower salinity, and then pulled back to the medium and high salinity area for cultivation in June of the following year. This cultivation method of Crassostrea hongkongensis requires a large amount of labor, high labor cost, and high technical requirements for farmers to judge the migration timing. Premature migration affects the growth, and late migration increases the mortality rate. However, in recent years, due to the reduction of fresh water inflow into the sea, the planning of the nearshore ecological red line, etc., the area suitable for migrating white oyster cultivation has decreased sharply. On the other hand, the increase in labor cost and the time-consuming and laborious migration work have made farmers miserable. Therefore, due to the influence of the above various factors, Crassostrea hongkongensis is still growing in medium and high salinity during the breeding period from March to May, resulting in a sharp increase in the mortality rate of Crassostrea hongkongensis, with a maximum mortality rate of 90%, bringing great economic losses to farmers, seriously dampening the enthusiasm of farmers for cultivation and seriously delaying the development and growth of the Crassostrea hongkongensis aquaculture industry. The increase in the mortality rate of Crassostrea hongkongensis during this period is mainly caused by the decrease in dissolved oxygen in water due to the increase in salinity, gonadal development, and the increase in seawater temperature. Farmers are urgently in need of cultivating a new strain of Crassostrea hongkongensis that is highly salt-tolerant, has poor gonadal development, and strong stress resistance. Summary of the Invention

[0004] The purpose of the present invention is to provide an excellent method for cultivating a new triploid strain of Crassostrea hongkongensis that is highly salt-tolerant and grows fast, which can cultivate a Crassostrea hongkongensis with high salt tolerance, poor fertility, fast growth, strong resistance, low mortality rate, good quality, and can be marketed throughout the year.

[0005] Through continuous breeding for high-salt tolerance, a new diploid strain of Hong Kong oysters that is tolerant to high salt can be cultivated. Triploids have the advantages of poor fertility, strong resistance, fast growth, and low mortality. Polyploid technology can be used to solve the high mortality problem caused by poor gonadal development and stress resistance. Therefore, a new triploid strain of Hong Kong oysters that is tolerant to high salt and grows fast can be cultivated by combining selective breeding technology with polyploid breeding technology to solve the industrial problems faced by Hong Kong oyster farming. In addition, triploids have poor fertility and cannot be directly bred. By controlling tetraploid germplasm, the seed rights of new triploid oyster strains can be controlled. Controllable seed rights are conducive to the active promotion of new strains by seedling companies, the improvement of the coverage rate of oyster improved varieties, the improvement of the enthusiasm of germplasm research and development institutions, and the continuous genetic improvement of germplasm.

[0006] The present invention mainly relates to a method for cultivating a high-salt-tolerant and fast-growing triploid new strain of Hong Kong oysters, comprising the steps of screening a high-salt-tolerant diploid population, breeding a high-salt-tolerant and fast-growing diploid new strain, establishing a high-salt-tolerant and fast-growing tetraploid induction strain, breeding a high-salt-tolerant and fast-growing tetraploid new strain, and large-scale production of a high-salt-tolerant and fast-growing triploid new strain, and the method is characterized in that the method comprises the following steps:

[0007] Using growth, survival and total weight as screening indicators, we screened out high-salt-tolerant diploid populations with low mortality rates in both high-salt and low-salt waters. Then, using shell height as a screening indicator, we screened out new diploid strains that were tolerant to high salt and grew quickly. We then used this to bred a tetraploid induced strain that was tolerant to high salt and grew quickly. Then, using shell height as a screening indicator, we screened out new tetraploid strains that were tolerant to high salt and grew quickly. Using the new tetraploid strains that were tolerant to high salt and grew quickly and the new diploid strains that were tolerant to high salt and grew quickly as parents, we obtained new triploid strains that were tolerant to high salt and grew quickly.

[0008] The specific steps are:

[0009] a. Screening of diploid populations tolerant to high salt content: different geographical populations were collected in the main breeding areas of Hong Kong oysters with large salinity changes, and the broodstock were artificially temporarily cultured and matured in seawater with a salinity of 24‰ to 28‰, and then artificially dissected and identified for sex, and male and female individuals with well-developed gonads were selected, artificially fertilized, and the larvae were hatched and cultivated in seawater with a salinity of 24‰ to 28‰, and the hatching parameters of each group were recorded; the juveniles of different populations were simultaneously suspended in several sea areas with a salinity of 18‰ to 28‰ and several low-salinity sea areas with a salinity of less than 18‰, and the growth, survival, and total weight of each group were tracked and measured, and the diploid population with low mortality in both high-salinity and low-salinity sea areas was selected, which is the diploid population of Hong Kong oysters tolerant to high salt content;

[0010] b. Breeding of diploid new strains with high salt tolerance and fast growth: Randomly select individuals from the diploid population of Crassostrea hongkongensis with high salt tolerance in step a, temporarily culture them artificially and promote gonadal maturation, screen out individuals with the top shell heights, dissect them, perform artificial fertilization and cultivate larvae to obtain F1, and suspend and culture F1 in waters with a salinity of 18‰ - 28‰; Randomly select several surviving F1, temporarily culture them artificially and promote gonadal maturation, screen out individuals with the top shell heights as parents, perform artificial dissection, fertilization and cultivate larvae to obtain F2, and suspend and culture F2 in waters with a salinity of 18‰ - 28‰; Referring to the above conditions, continuously perform high-salt stress and selection of individuals with large shell heights for another generation to obtain F3, which is the diploid new strain of Crassostrea hongkongensis with high salt tolerance and fast growth;

[0011] c. Establishment of tetraploid induction lines with high salt tolerance and fast growth: Select several individuals from the diploid new strain of Crassostrea hongkongensis with high salt tolerance and fast growth in step b, screen out individuals with the top shell heights as parents, after artificial dissection and fertilization, use 6-DMAP to inhibit the release of the second polar body to obtain triploids with high salt tolerance and fast growth; Promote the gonadal maturation of the triploids with high salt tolerance and fast growth, screen out fertile female individuals, and at the same time use the diploid new strain with high salt tolerance and fast growth in step b as the male parent source. After fertilization of the fertile triploid female individuals and diploid male individuals, use CB to inhibit the release of the second polar body to obtain tetraploid induction lines with high salt tolerance and fast growth;

[0012] d. Breeding of tetraploid new strains with high salt tolerance and fast growth: Randomly select the tetraploid induction lines with high salt tolerance and fast growth in step c, screen out individuals with the top shell heights as parents, perform artificial dissection, fertilization and incubate and cultivate tetraploid larvae in high-salt seawater with a salinity of 26‰, and then culture the tetraploid juvenile clams in waters with a salinity of 18‰ - 28‰, which is tetraploid F1; According to the above steps, similarly screen out F1 with the top shell heights as parents, perform artificial fertilization and high-salt stress culture to obtain F2, which is the tetraploid new strain of Crassostrea hongkongensis with high salt tolerance and fast growth;

[0013] e. Production of triploid new strains with high salt tolerance and fast growth: Temporarily culture and promote the gonadal maturation of the diploid new strain of Crassostrea hongkongensis with high salt tolerance and fast growth in step b and the tetraploid new strain of Crassostrea hongkongensis with high salt tolerance and fast growth in step d in seawater with a salinity of 24‰ - 28‰; Then perform artificial dissection and identify the ploidy of the tetraploids, screen out diploid females and tetraploid males, and fertilize, incubate and cultivate them in seawater with a salinity of 26‰, which is the triploid new strain of Crassostrea hongkongensis with high salt tolerance and fast growth.

[0014] Through the above steps, a triploid new strain of Crassostrea hongkongensis with high salt tolerance and fast growth is obtained. This new strain has the advantages of high salt tolerance, fast growth, poor fertility, strong stress resistance, high quality, and being marketable throughout the year.

[0015] Preferably, the main cultivation area of *Crassostrea hongkongensis* described in step a refers to the cultivation area of *Crassostrea hongkongensis* where the salinity variation range is 18‰ - 28‰ and the salinity exceeds 24‰ for more than 4 months every year.

[0016] Preferably, the different geographical populations described in step a refer to oyster populations with wild settlement as the seedling source, different settlement locations, and having been cultivated for more than 2 years.

[0017] Preferably, the well-developed male and female individuals described in step a mean that the sperm of male individuals beats actively under the microscope when placed in seawater and there are few spermatocytes, and more than 80% of the eggs of female individuals become round within 40 minutes after being placed in seawater, and the eggs are intact and of the same size.

[0018] Preferably, the hatching parameters described in step a refer to the fertilization rate, cleavage rate, and D-larva rate.

[0019] Preferably, screening out the new diploid strain with low mortality rates in both high-salinity and low-salinity sea areas in step a is to ensure that the screened diploid population retains the characteristics of *Crassostrea hongkongensis* adapting to low salinity while tolerating high salinity, because the cultivation area of *Crassostrea hongkongensis* is close to the estuary area, with a large salinity variation range, and the seawater salinity will be relatively low for some time.

[0020] Preferably, the high-salinity stress tolerance described in step b includes that artificial fertilization, hatching, larval cultivation, juvenile oyster intermediate culture, and offshore culture all need to undergo high-salinity stress selection.

[0021] Preferably, the individuals with the top shell heights screened in step b are the top 5% of the individuals in terms of shell height. The reason for using them as parents is to breed a new fast-growing diploid strain of *Crassostrea hongkongensis*.

[0022] Preferably, for the artificial temporary rearing and ripening described in step b, the seawater salinity is 24‰ - 28‰, and the seawater for cultivating larvae has a salinity of 26‰.

[0023] Preferably, when using 6-DMAP to inhibit the release of the second polar body in step c, the concentration of 6-DMAP is 100 mg / L, the density of the treated eggs is 1×10 7 individuals / L, the treatment timing is 20 min after fertilization, and the treatment duration is 25 min.

[0024] Preferably, when using CB to inhibit the release of the second polar body in step c, the concentration of CB is 0.40 mg / L, the density of the treated eggs is 5×10 6 individuals / L, the treatment timing is 30 min after fertilization, and the treatment duration is 45 min.

[0025] Preferably, screening and identifying tetraploid individuals in step d means identifying tetraploids using a flow cytometer with diploids as a control.

[0026] The present invention combines selective breeding and polyploid breeding techniques. By collecting different geographical populations and screening for high-salt-tolerant strains, and then through continuous high-salt stress and shell height selection for three generations, a new diploid strain of the Hong Kong oyster that is high-salt-tolerant and grows fast is obtained. Then, tetraploid induction techniques for the Hong Kong oyster that is high-salt-tolerant and grows fast are used to obtain a tetraploid induction line of the Hong Kong oyster that is high-salt-tolerant and grows fast. Furthermore, high-salt stress and shell height selection are carried out for two generations to obtain a new tetraploid strain of the Hong Kong oyster that is high-salt-tolerant and grows fast. Finally, the male of the new tetraploid strain that is high-salt-tolerant and grows fast is crossed with the female of the new diploid strain that is high-salt-tolerant and grows fast to obtain a new triploid strain of the Hong Kong oyster that is high-salt-tolerant and grows fast, successfully achieving the genetic improvement of the Hong Kong oyster in terms of high-salt tolerance, poor fertility, and fast growth.

[0027] Based mainly on the industrial problems of the diploid Hong Kong oyster, such as its inability to tolerate high salinity, long gonadal development cycle, high mortality, poor quality, slow growth, and inability to be marketed throughout the year, the present invention conducts high-salt stress, growth selection, and polyploid breeding on the Hong Kong oyster through the scientific and effective combination of selective breeding and polyploid breeding, with the aim of obtaining a new triploid strain of the Hong Kong oyster that is high-salt-tolerant and grows fast. The present invention makes full use of the improvement of the high-salt tolerance and growth traits of the Hong Kong oyster by selective breeding technology and the improvement of the gonadal development of the Hong Kong oyster by polyploid breeding technology, obtaining a new strain with both the advantages of selection and polyploidy, having the advantages of high-salt tolerance, poor fertility, fast growth, strong stress resistance, good quality, and being marketable throughout the year, and having great potential and value for commercial promotion and application. The new triploid strain of the Hong Kong oyster that is high-salt-tolerant and grows fast obtained by the present invention has a survival rate increase of 126.19% - 207.84% and a growth increase of 55.10% - 64.40% in high-salt waters (salinity 20‰ - 28‰) compared with the unselected diploid Hong Kong oyster, and the fertile proportion is reduced to 8.74% - 11.37% (diploid is 100% fertile). Compared with the diploid Hong Kong oyster that is high-salt-tolerant and grows fast, the survival rate is increased by 21.55% - 24.92%, the growth is increased by 9.75% - 12.65%, and the fertile proportion is reduced by 8.74% - 11.37% (diploid is 100% fertile).

[0028] The present invention has significantly improved the high-salt tolerance, growth, and fertility performance of the Hong Kong oyster. The obtained high-salt-tolerant new strain grows fast and has poor fertility at the same time, and the poor fertility is beneficial to the protection of the new strain's variety rights. Therefore, the present invention has the advantages of strong adaptability, great potential for commercial application, easy protection of variety rights, and strong operability. Detailed Embodiments

[0029] The following examples are used to illustrate in detail a method for cultivating a new triploid strain of the Hong Kong oyster that is high-salt-tolerant and grows fast provided by the present invention, and it is not a limitation to the present invention.

[0030] Example 1

[0031] a. Screening of diploid populations of Crassostrea hongkongensis resistant to high salinity: 300 individuals cultured for 2 years were collected from 8 sea areas with large annual salinity variation ranges, namely Zhulin in Beihai, Guangxi; Dafengjiang in Beihai, Guangxi; Xiniu Jiao in Qinzhou, Guangxi; Qinzhou Bonded Port in Guangxi; Pearl Bay in Fangchenggang, Guangxi; Niutianyang in Shantou, Guangdong; Donghai Island in Zhanjiang, Guangdong; and Chuandao in Taishan, Guangdong. The individuals were temporarily cultured and promoted to maturity for 15 days in seawater with a salinity of 24‰ - 28‰. Then, they were arranged in descending order of shell height, and the first 30 were taken as parents. The parents were dissected manually to identify the sexes. The eggs were squeezed out and hydrated in seawater with a salinity of 26‰ until 80% of the eggs became round. Then, individuals with good sperm motility were selected, and the eggs and sperm were mixed for fertilization. The fertilized eggs were placed in fresh seawater with a salinity of 26‰ for hatching, and the fertilization rate, cleavage rate, and D-larva rate of each group were recorded. The larvae were cultured and attached to the attachment substrate. Then, the juvenile clams of the 8 populations were simultaneously suspended and cultured in 3 high-salinity sea areas, namely Zhulin in Beihai, Guangxi (salinity variation range: 22‰ - 28‰), Dafengjiang in Beihai, Guangxi (18‰ - 26‰), and Donghai Island in Zhanjiang, Guangdong (20‰ - 28‰), and 2 low-salinity sea areas, namely Maowei Sea in Qinzhou, Guangxi (10‰ - 16‰) and Hengqin in Zhuhai, Guangdong (5‰ - 18‰). The survival rate, shell height, and total weight of the 8 groups in each sea area were tracked and measured over 2 years. The phenotypic data of the 8 groups in each sea area were compared, and through comprehensive analysis, the group - Qinzhou Bonded Port in Guangxi, which performed well in all 3 high-salinity sea areas and 2 low-salinity sea areas, was selected. This is the diploid population of Crassostrea hongkongensis resistant to high salinity.

[0032] b. Selection and breeding of a new diploid strain of Crassostrea hongkongensis that is highly salt-tolerant and grows fast: In April 2013, 600 individuals were randomly selected from the highly salt-tolerant diploid population of Crassostrea hongkongensis in step a, temporarily cultured and promoted to maturity in seawater with a salinity of 24‰ - 28‰. They were arranged in descending order of shell height, and the top 5% (i.e., 30 individuals) were taken as the parental stock for the selection group. The parental stock in the selection group was anatomically dissected and identified for male and female. Eggs were squeezed out and soaked in seawater with a salinity of 26‰ until 80% of the eggs became round. Active sperm were selected for artificial fertilization, and the fertilized eggs were hatched and cultured in seawater with a salinity of 26‰. This was the highly salt-tolerant F1. After attachment, F1 was suspended and cultured in the Dafengjiang Sea area of Beihai for 2 years. In March 2015, 600 individuals were randomly selected from F1, temporarily cultured and promoted to maturity in seawater with a salinity of 24‰ - 28‰. They were arranged in descending order of shell height, and the top 5% (i.e., 30 individuals) were taken as the parental stock for the selection group. The parental stock in the selection group was anatomically dissected and identified for male and female. Eggs were squeezed out and hydrated in seawater with a salinity of 26‰ until 80% of the eggs became round. Active sperm were selected for artificial fertilization, and the fertilized eggs were hatched and cultured in seawater with a salinity of 26‰. This was the highly salt-tolerant F2. After attachment, F2 was suspended and cultured in the Dafengjiang Sea area of Beihai for 2 years. In May 2017, referring to the selection procedure of F2 above, F2 was continuously selected for 1 generation to obtain F3, and F3 was the new diploid strain of Crassostrea hongkongensis that is highly salt-tolerant and grows fast. At the same time, during each generation of selection, 30 individuals were randomly selected from the highly salt-tolerant diploid population of Crassostrea hongkongensis in step a as the parental stock for the control group. The control group was temporarily cultured, promoted to maturity, anatomically dissected, fertilized, and cultured in normal seawater with a salinity of 15‰. After attachment, they were suspended and cultured in the Dafengjiang Sea area of Beihai at the same time, and the growth and survival of the selection group and the control group were tracked and measured.

[0033] c. Establishment of a tetraploid induction line that is highly salt-tolerant and grows fast: In June 2018, 600 individuals were randomly selected from the new diploid strain of Crassostrea hongkongensis that is highly salt-tolerant and grows fast in step b, temporarily cultured and promoted to maturity in seawater with a salinity of 24‰ - 28‰. They were arranged in descending order of shell height, and the top 5% (i.e., 30 individuals) were taken as the parental stock for the selection group. The parental stock in the selection group was anatomically dissected and identified for male and female. Eggs were squeezed out and hydrated in seawater with a salinity of 26‰ until 80% of the eggs became round. Active sperm were selected for artificial fertilization. The fertilized eggs were concentrated with a 500-mesh silk screen and the fertilized eggs were placed according to 1×10 7Incubate in seawater with a salinity of 26‰ at a density of / L. Treat continuously with 100 mg / L of 6-DMAP for 25 min 20 min after fertilization, then wash off the drug with a 500-mesh silk screen, and place the eggs in fresh seawater with a salinity of 26‰ for normal incubation, cultivation and attachment. After attachment, suspend and culture in the Dafengjiang Sea area of Beihai. This is the triploid that is highly salt-tolerant and grows fast; in June 2019, select the 1-year-old fertile female triploids that are highly salt-tolerant and grow fast, squeeze out the eggs and soak them in seawater with a salinity of 26‰ until the eggs become round. Then select 1 diploid individual of Crassostrea hongkongensis that is highly salt-tolerant and grows fast with high sperm activity as the male parent, perform artificial fertilization and adjust the egg density to 5×10 6 individuals / L. Treat with cytochalasin B (CB) at a concentration of 0.40 mg / L for 45 min 30 min after fertilization, wash off the drug with a 500-mesh silk screen and place it in fresh seawater with a salinity of 26‰ for normal incubation, cultivation and attachment. This is the tetraploid induction line that is highly salt-tolerant and grows fast.

[0034] d. Breeding of a new tetraploid strain of Crassostrea hongkongensis that is highly salt-tolerant and grows fast: In May 2020, take the 1-year-old tetraploid induction line individuals in step c, temporarily culture and ripen them artificially in seawater with a salinity of 24‰ - 28‰, detect the ploidy with a flow cytometer and identify 300 tetraploids. Take the top 5% in shell height, that is, 15 individuals as parents, perform artificial fertilization and incubate and cultivate tetraploid larvae in high-salinity seawater with a salinity of 26‰. After attachment, suspend and culture the juvenile shells in the sea area with a salinity of 18‰ - 28‰. This is the highly salt-tolerant tetraploid F1; in June 2021, similarly, take the 1-year-old highly salt-tolerant tetraploid F1, temporarily culture and ripen them artificially in seawater with a salinity of 24‰ - 28‰, identify 300 by flow cytometry, take the individuals in the top 5% of shell height as parents for artificial fertilization, and then incubate and cultivate in high-salinity seawater with a salinity of 26‰. After attachment, suspend and culture the juvenile shells in the sea area with a salinity of 18‰ - 28‰. This is the new tetraploid strain of Crassostrea hongkongensis that is highly salt-tolerant and grows fast;

[0035] e. Production of a new triploid strain that is highly salt-tolerant and grows fast: In May 2022, take the new tetraploid strain of Crassostrea hongkongensis that is highly salt-tolerant and grows fast in step d and the new diploid strain of Crassostrea hongkongensis that is highly salt-tolerant and grows fast in step b, and acclimatize and ripen them simultaneously in seawater with a salinity of 24‰ - 28‰; Manually dissect the parents, flow cytometry identify the tetraploids in the new tetraploid strain, take the sperm of tetraploid males and the eggs of diploid females for artificial fertilization, and incubate and cultivate them in high-salt seawater with a salinity of 26‰, which is the new triploid strain that is highly salt-tolerant and grows fast; Suspend the cultivation of the new triploid strain of Crassostrea hongkongensis that is highly salt-tolerant and grows fast, the new diploid strain of Crassostrea hongkongensis that is highly salt-tolerant and grows fast, and the unselected diploid of Crassostrea hongkongensis simultaneously in Dafengjiang, Beihai, Guangxi (salinity 20‰ - 28‰) and Haishan, Chaozhou, Guangdong (salinity 18‰ - 26‰), and track and measure their survival, shell height, total weight, and gonadal development. The results show that the survival rate of the new triploid strain of Crassostrea hongkongensis that is highly salt-tolerant and grows fast in high-salt waters (salinity 20‰ - 28‰) is increased by 126.19% - 207.84%, growth is increased by 55.10% - 64.40%, and the fertile proportion is reduced to 8.74% - 11.37% (100% fertile for diploids) compared with the unselected diploid of Crassostrea hongkongensis, and the survival rate is increased by 21.55% - 24.92%, growth is increased by 9.75% - 12.65%, and the fertile proportion is reduced by 8.74% - 11.37% (100% fertile for diploids) compared with the new diploid strain of Crassostrea hongkongensis that is highly salt-tolerant and grows fast in high-salt waters.

Claims

1. A method for cultivating a new triploid strain of Hong Kong oysters that is tolerant to high salt and grows fast, characterized in that: The specific steps are: a. Screening of diploid populations tolerant to high salt content: different geographical populations were collected in the main breeding areas of Hong Kong oysters with large salinity changes, and the broodstock were artificially temporarily cultured and matured in seawater with a salinity of 24‰ to 28‰, and then artificially dissected and identified for sex, and male and female individuals with well-developed gonads were selected, artificially fertilized, and the larvae were hatched and cultivated in seawater with a salinity of 24‰ to 28‰, and the hatching parameters of each group were recorded; the juveniles of different populations were simultaneously suspended in several sea areas with a salinity of 18‰ to 28‰ and several low-salinity sea areas with a salinity of less than 18‰, and the growth, survival, and total weight of each group were tracked and measured, and the diploid population with low mortality in both high-salinity and low-salinity sea areas was selected, which is the diploid population of Hong Kong oysters tolerant to high salt content; b. Breeding of a new diploid strain that is tolerant to high salt and grows fast: randomly select individuals of the Hong Kong oyster diploid group that is tolerant to high salt in step a, artificially temporarily culture and accelerate maturity, select individuals with the highest shell height, dissect, artificially fertilize and cultivate larvae to obtain F1, and hang the F1 in a sea area with a salinity of 18‰ to 28‰; randomly select a number of surviving F1, artificially temporarily culture and accelerate maturity, select individuals with the highest shell height as parents, artificially dissect, fertilize and cultivate larvae to obtain F2, and hang the F1 in a sea area with a salinity of 18‰ to 28‰; referring to the above conditions, continue high salt stress and shell height selection for one generation to obtain F3, which is a new diploid strain of Hong Kong oysters that is tolerant to high salt and grows fast; c. Establishment of a tetraploid induction line that is tolerant to high salt and grows fast: take several diploid new strains of Hong Kong oysters that are tolerant to high salt and grow fast in step b, screen out individuals with the highest shell height as parents, and after artificial dissection and fertilization, use 6-DMAP to inhibit the release of the second polar body to obtain a triploid that is tolerant to high salt and grows fast; ripen the triploid that is tolerant to high salt and grows fast, screen out female individuals with fertile gonads, and use the diploid new strain that is tolerant to high salt and grows fast in step b as the source of the father, and after fertilizing the fertile triploid female individuals and the diploid male individuals, use CB to inhibit the release of the second polar body to obtain a tetraploid induction line that is tolerant to high salt and grows fast; d. Breeding of a new tetraploid strain that is tolerant to high salt and grows fast: randomly select the tetraploid induced strain that is tolerant to high salt and grows fast in step c, select the individuals with the highest shell height as parents, perform artificial dissection, fertilization, and hatch and cultivate tetraploid larvae in high-salinity seawater with a salinity of 26‰, and then culture the tetraploid spat in a sea area with a salinity of 18‰ to 28‰, which is tetraploid F1; according to the above steps, similarly select the F1 with the highest shell height as parents, perform artificial fertilization and high-salinity stress culture, and obtain F2, which is a new tetraploid strain of Hong Kong oysters that is tolerant to high salt and grows fast; e. Production of a new triploid strain that is tolerant to high salt and grows fast: The diploid new strain of Hong Kong oysters that is tolerant to high salt and grows fast in step b and the tetraploid new strain of Hong Kong oysters that is tolerant to high salt and grows fast in step d are temporarily cultured and ripened in seawater with a salinity of 24‰ to 28‰; then the tetraploid ploidy is manually dissected and identified, and the diploid females and tetraploid males are screened out, and fertilized, hatched and cultivated in seawater with a salinity of 26‰ to obtain a new triploid strain of Hong Kong oysters that is tolerant to high salt and grows fast.

2. The cultivation method according to claim 1, characterized in that The main Hong Kong oyster culture area described in step a refers to a Hong Kong oyster culture area where the salinity varies between 18‰ and 28‰ and the salinity exceeds 24‰ for more than 4 months each year.

3. The cultivation method according to claim 1, characterized in that The different geographical communities mentioned in step a refer to oyster communities whose seed sources are wild attached seed, which are attached at different locations and have been cultured for more than 2 years.

4. The cultivation method according to claim 1, characterized in that The male and female individuals with well-developed gonads in step a refer to male individuals whose spermatozoa are actively beating and have few spermatocytes under a microscope when placed in seawater, and female individuals whose eggs are more than 80% rounded within 40 minutes after being placed in seawater and whose eggs are intact and of uniform size.

5. The cultivation method according to claim 1, characterized in that: The hatching parameters described in step a refer to fertilization rate, cleavage rate and D larvae rate.

6. The cultivation method according to claim 1, characterized in that: The high-salt stress described in step b includes hatching after artificial fertilization, larval cultivation, juvenile spat culture and offshore aquaculture, all of which need to be subjected to high-salt stress breeding; the individuals with the highest shell height selected in step b are the individuals in the top 5% of shell height, and the reason for them being used as parents is to select a new diploid strain of Hong Kong oysters with fast growth; the artificial temporary cultivation and accelerated maturation described in step b has a seawater salinity of 24‰ to 28‰, and the seawater for cultivating the larvae has a salinity of 26‰.

7. The cultivation method according to claim 1, characterized in that: When 6-DMAP was used to inhibit the release of the second polar body in step c, the concentration of 6-DMAP was 100 mg / L and the egg density was 1×10 7 / L, the treatment time was 20 minutes after fertilization, and the treatment duration was 25 minutes.

8. The cultivation method according to claim 1, characterized in that: When CB was used to inhibit the release of the second polar body in step c, the CB concentration was 0.40 mg / L and the egg density was 5×10 6 / L, the treatment time was 30 minutes after fertilization, and the treatment duration was 45 minutes.

9. The cultivation method according to claim 1, characterized in that: The breeding of a new tetraploid strain that is tolerant to high salt and grows fast in step d refers to identifying the tetraploid by flow cytometry while using the diploid as a control.