A method for cultivating high-salt-tolerant seedlings of Omi oysters

Abstract

The present invention discloses a method for cultivating high-salt-tolerant seedlings of Crassostrea gigas, and belongs to the technical field of oyster seedling cultivation. The method for cultivating high-salt-tolerant seedlings of the present invention comprises the following steps: raising the salinity and the temperature alternately during the temporary rearing and maturation of the parents to ensure the quality of sperm and eggs and to have a certain degree of high-salt tolerance; raising the salinity once in the later stage of larval rearing; applying salinity stress once after attachment and metamorphosis, and temporarily rearing and protecting the seedlings in a normal high-salt sea area, and finally obtaining Crassostrea gigas seedlings with obvious tolerance to high salt. The method for cultivating high-salt-tolerant seedlings provided by the present invention effectively improves the salt tolerance of Crassostrea gigas seed shells and offspring, can obtain a population of offspring with a certain degree of high-salt tolerance in a short time, shortens the breeding time, and improves the breeding efficiency. The obtained seedlings can be cultured in high-salt deep-water sea areas, expand the breeding range of Crassostrea gigas, increase the yield of Crassostrea gigas, promote the diversification of oyster farming, and provide diversified oyster products.

Description

Technical Field

[0001] The invention belongs to the technical field of oyster seedling cultivation, and particularly relates to a method for cultivating high-salt-resistant seedlings of Omi oysters. Background Art

[0002] The Omi oyster (Crassostrea ariakensis) is distributed along the coast from the Lizi River in the north to Hainan Island in the south. Named for its peak growth in estuaries where freshwater flows into the sea, it is nutritious and delicious, making it a popular commodity for consumers and a key commercial shellfish in my country. Omi oysters are a key aquaculture species in the South China Sea. Their abundance in northern China has been declining, and they were once considered functionally extinct in northern my country. Although large Omi oyster reefs have been discovered in coastal areas such as Dongying and Binzhou in Shandong Province, large-scale aquaculture has yet to be established in northern China.

[0003] Salinity affects the physiological and metabolic state of marine organisms, determines their growth and distribution, and is an important ecological factor in marine ecosystems. When salinity rises, marine organisms need to adjust osmotic pressure, change respiration, feed intake, and other stress responses to maintain their homeostasis. Stress responses consume a large amount of energy, which can cause the death of some or all organisms. Although the Omi oyster is a euryhaline species, its tolerance to high salt levels is relatively weak. Its optimal survival salinity is 10-25‰, and its optimal growth salinity is 20-25‰. Therefore, it is only distributed in estuaries with lower salinity. High salinity is also one of the factors that restrict the large-scale promotion of Omi oyster aquaculture in northern China. Research on China's Omi oysters is mostly focused on seedling breeding and interspecific hybridization. The impact of salinity on Omi oysters is also mostly focused on the physiological response of Omi oysters to salinity stress. When breeding Omi oyster seedlings, the source of parents is mainly naturally mature parents in natural sea areas or parents that are matured by heating under low-salt conditions. Juvenile cultivation is also carried out under low-salt conditions. The obtained seedlings are only suitable for farming in low-salt sea areas. The problem of seedlings' intolerance to high salt has not been effectively solved.

[0004] Establishing technical methods for cultivating high-salt-tolerant Omi oyster seedlings and obtaining large quantities of high-salt-tolerant Omi oyster seedlings can expand the Omi oyster farming area, area and output, provide the public with more diversified oyster products, and meet people's growing needs for a better life. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for cultivating high-salt-tolerant seedlings of Omi oysters, effectively improving the high-salt tolerance of Omi oyster seed shells and offspring, obtaining a progeny population with a certain high-salt tolerance in a short period of time, shortening the breeding time, and improving the breeding efficiency.

[0006] The present invention provides a method for cultivating high-salt-tolerant seedlings of Crassostrea gigas, comprising the following steps: (1) collecting wild Crassostrea gigas parents and temporarily cultivating them, during which the cultivation temperature is increased from the natural water temperature to 24°C, and the salinity is gradually increased from 20‰ to 28‰;

[0007] (2) collecting sperm and eggs from mature gonadal parents, artificially inseminating them and incubating them in an environment with a salinity of 28‰. After the larvae develop into D-shaped larvae, the salinity is gradually increased to 30‰. After some larvae have eyespots, they are placed on a substrate; the temperature in the environment is 24-26°C.

[0008] (3) After the larvae develop into juveniles with an average body length of 500 μm, they are cultured in a stress environment with a salinity of 35‰ and then transferred to normal seawater for cultivation.

[0009] Preferably, the temporary culture in step (1) comprises: in a first temporary culture stage, maintaining the salinity at 20‰ and gradually increasing the water temperature to 15°C;

[0010] In the second temporary rearing stage, the salinity is gradually increased to 25‰ and the water temperature is increased to 18℃;

[0011] In the third temporary rearing stage, the salinity is maintained at 25‰ and the water temperature is gradually increased to 24℃;

[0012] In the fourth temporary rearing stage, the salinity is gradually increased to 28‰ and the water temperature is maintained at 24℃.

[0013] Preferably, the first temporary raising stage, the second temporary raising stage, the third temporary raising stage and the fourth temporary raising stage are all 7 to 10 days.

[0014] Preferably, during each temporary rearing stage, the parents are moved to the pond once a day before the temperature exceeds 24°C, and the water is changed twice a day after the temperature reaches 24°C, with each water change amount being 40-60%.

[0015] Preferably, during the temporary culture period of step (1), the feed includes diatoms, chlorella, golden algae and flat algae.

[0016] Preferably, after the larvae in step (2) develop into D-type larvae, the salinity is slowly increased to 30‰ within 5 days.

[0017] Preferably, the larvae culture density in step (2) is: after selection and breeding, the density is 5 to 6 per ml, and after the shell length reaches 300 μm, the density is 1 to 2 per ml.

[0018] Preferably, the stress culture time in step (3) is 96 hours.

[0019] Preferably, in step (3), when the juvenile spat grows to 800-1000 μm, they are moved to a pond or natural sea area (salinity 32‰) for temporary rearing, and then cultured in a cage or in a fry cage.

[0020] Preferably, the change in salinity in step (1), step (2) or step (3) is achieved by changing water.

[0021] Beneficial effects: The present invention provides a method for cultivating high-salt-tolerant seedlings of Crassostrea gigas. During the temporary rearing and maturation of the parents, the salinity and temperature are alternately increased to ensure the quality of sperm and eggs and a certain degree of high-salt tolerance; the salinity is increased once in the later stage of larval rearing; salinity stress is applied once after attachment and metamorphosis, and temporary rearing and seedling conservation are carried out in a normal high-salt sea area, finally obtaining Crassostrea gigas seedlings with obvious tolerance to high salt. The method for cultivating high-salt-tolerant seedlings provided by the present invention, firstly, effectively improves the salt tolerance of Crassostrea gigas seed shells and offspring, and secondly, can obtain a population of offspring with a certain degree of high-salt tolerance in a short period of time, shortening the breeding time and improving the breeding efficiency. The obtained seedlings can be cultured in high-salt deep-water sea areas, expanding the breeding range of Crassostrea gigas, increasing the yield of Crassostrea gigas, promoting the diversification of oyster farming, and providing diversified oyster products. DETAILED DESCRIPTION

[0022] The present invention provides a method for cultivating high-salt-tolerant seedlings of Crassostrea gigas, comprising the following steps: (1) collecting wild Crassostrea gigas parents and temporarily cultivating them, during which the cultivation temperature is increased from the natural water temperature to 24°C, and the salinity is gradually increased from 20‰ to 28‰;

[0023] (2) collecting sperm and eggs from mature gonadal parents, artificially inseminating them and incubating them in an environment with a salinity of 28‰. After the larvae develop into D-shaped larvae, the salinity is gradually increased to 30‰. After some larvae have eyespots, they are placed on a substrate; the temperature in the environment is 24-26°C.

[0024] (3) After the larvae develop into juveniles with an average body length of 500 μm, they are cultured in a stress environment with a salinity of 35‰ and then transferred to normal seawater for cultivation.

[0025] The present invention first performs temporary culture to promote the maturation of broodstock. Wild Omi oyster broodstock are collected and then cultured temporarily. During the culture period, the culture temperature is increased from the natural water temperature to 24°C, and the salinity is gradually increased from 20‰ to 28‰. The present invention preferably collects broodstock from natural sea areas in mid-to-late April and then culture them in ponds. The culture preferably includes: a first culture stage, maintaining the salinity at 20‰ and gradually increasing the water temperature to 15°C;

[0026] In the second temporary rearing stage, the salinity is gradually increased to 25‰ and the water temperature is gradually increased to 18℃;

[0027] In the third temporary rearing stage, the salinity is maintained at 25‰ and the water temperature is gradually increased to 24℃;

[0028] In the fourth temporary rearing stage, the salinity is gradually increased to 28‰ and the water temperature is maintained at 24℃.

[0029] The first temporary rearing stage, the second temporary rearing stage, the third temporary rearing stage and the fourth temporary rearing stage of the present invention are preferably all 7 to 10 days. For example, in the embodiment of the present invention, the first temporary rearing stage is 7 days, the second temporary rearing stage is 10 days, the third temporary rearing stage is 10 days, and the fourth temporary rearing stage is 9 days. The present invention preferably transfers the parent to the pond once a day before the temperature exceeds 24°C in each temporary rearing stage, and changes the water twice a day after 24°C, with the amount of water changed each time being about half of 40 to 60%. In the present invention, in the first three temporary rearing stages, the salinity and temperature are increased by a certain amount every day by inverting the pond, and the target salinity or temperature is reached on the last day of the temporary rearing stage; in the fourth temporary rearing stage, the salinity is increased by changing the water, and finally the target salinity is reached. During the said rearing period of the present invention, the feed preferably includes feeding diatoms, chlorella, golden algae and flat algae.

[0030] After the temporary rearing, the present invention enters larval culture, specifically including dissecting the juveniles to obtain sperm and eggs after the parent shellfish's gonads mature, and completing artificial insemination before hatching. During the fertilization and hatching described in the present invention, the salinity is preferably maintained at 28‰, and the water temperature is maintained between 24 and 26°C to avoid large fluctuations. The present invention preferably selects the best larvae after they develop into D-shaped larvae and transfers them to a cultivation pond for cultivation. More preferably, when the larvae grow to 200μm, the salinity is slowly increased to 30‰ by changing the water within 5 days. The salinity is then maintained at 30‰, and after 20% of the larvae have eyespots, the attachment substrate is added. The cultivation density of the larvae of the present invention is 5 to 6 per ml after selection, and 1 to 2 per ml after the shell length reaches 300μm in the later stage. After selection, golden algae are fed, and after one week of cultivation, diatoms, flat algae, and chlorella are gradually added.

[0031] After the larval culture stage, the present invention enters the juvenile spat stage management. During and after the juvenile metamorphosis, the salinity is controlled at 30‰. When the juvenile spat grows to 500 μm, the salinity is placed in water with a salinity of 35‰ for 96 hours, and then the salinity is reduced to 32‰. When the juvenile spat grows to 800-1000 μm, it is removed from the pond and moved to a pond or natural sea area (salinity 32‰) for temporary rearing, and then clipped or caged for culture.

[0032] To further illustrate the present invention, the following describes in detail a method for cultivating high-salt-tolerant seedlings of Crassostrea gigas provided by the present invention in conjunction with examples, but they should not be construed as limiting the scope of protection of the present invention.

[0033] Example 1

[0034] Two experimental groups were set up: a low-salt group and a gradually increasing salinity group.

[0035] 1. Temporary cultivation of seed shellfish to promote their maturity

[0036] On April 15th, the oysters were wild oysters collected from Dingzi Bay in Laiyang. After removing any debris from the shells and scrubbing them clean, they were placed in floating cages for temporary cultivation and maturation. The inlet temperature was 13.5°C and the salinity was 20‰.

[0037] Temporary culture stage I (7 days): The salinity of the low-salt and high-salt groups was maintained at 20‰, and the temperature was naturally increased from 13.5℃ to 15℃;

[0038] Temporary culture stage II (10 days): The salinity for the low-salt group was maintained at 20‰, while the salinity for the high-salt group was gradually increased from 20‰ to 25‰ (by 0.5‰ per day). The ripening temperature for both the low-salt and high-salt groups was uniformly increased from 15°C to 18°C (by 0.3°C per day).

[0039] Temporary culture stage III (10 days): The salinity for the low-salt group was maintained at 20‰, and the salinity for the high-salt group was maintained at 25‰. The ripening temperature for both the low-salt and high-salt groups was uniformly increased from 18°C to 24°C (0.6°C per day).

[0040] Temporary culture stage IV (9 days): The salinity for the low-salt group was maintained at 20‰, while the salinity for the high-salt group was gradually increased from 25‰ to 28‰ (0.3‰ per day). The ripening temperature for both the low-salt and high-salt groups was maintained at 24°C.

[0041] 2. Larval cultivation

[0042] On May 20th, after the broodstock's gonads matured, sperm and eggs were dissected and incubated. Fertilization and incubation took place at a salinity of 20‰ for the low-salt group and 28‰ for the high-salt group. The incubation water temperature was maintained between 24 and 26°C to avoid large fluctuations. After the larvae developed into D-shaped larvae, they were selected and transferred to the rearing pond for cultivation.

[0043] Cultivation stage I (9 days): the salinity of the low-salt group was controlled at 20‰, and the salinity of the high-salt group was maintained at 28‰.

[0044] Cultivation stage II (5 days): The salinity of the low-salt group was maintained at 20‰; when the larvae in the high-salt group grew to 200 μm, the salinity was slowly increased to 30‰ by changing the water within 5 days (increased by 0.4‰ per day).

[0045] Incubation stage III (6 days): The salinity in the low-salt group was maintained at 20‰; the salinity was controlled at 30‰. On June 10, after 20% of the larvae had developed eyespots, the cultch was released.

[0046] The larval culture temperature is 24-26℃, avoiding large fluctuations; the early culture density is 5-6 / ml, and the later culture density is 1-2 / ml; golden algae are fed in the early stage, and diatoms, flat algae, and chlorella are gradually added in the later stage.

[0047] 3. Management of Juvenile Spat

[0048] Juvenile stage I (5 days): During and after the metamorphosis of the larvae, the salinity is controlled at 30‰.

[0049] Juvenile stage II (4 days): Juveniles grow to an average of 500 μm and are placed in water with a salinity of 35‰ for 96 hours, and then moved to normal seawater (32‰) for culture.

[0050] Juvenile spat stage III (5 days): On June 24, the juvenile spat had grown to more than 800 μm and were moved to a pond or natural sea area (salinity 32‰) for temporary rearing, and then were clipped or caged for culture.

[0051] 4. Comparison of larval growth and survival

[0052] Fertilization rate: The fertilization rate of the high-salinity parent in a high-salinity environment was 95.41%, while the fertilization rate of the low-salinity parent in a high-salinity environment was 81.71%. The fertilization rate was significantly higher when the fertilization salinity was consistent with the parent culture salinity than when it was inconsistent.

[0053] Hatching rate: The hatching rate of the high-salt parent in a high-salt environment was 96.09%, and the hatching rate of the low-salt parent in a high-salt environment was 84.15%.

[0054] Larval growth: The high-salt parent grew faster in a high-salt environment, reaching the conditions for placement of the attachment substrate at the 26th day of age, with an average daily growth of 10.09 μm; the low-salt parent grew relatively slowly in a high-salt environment, reaching the conditions for placement of the attachment substrate at the 28th day of age, with an average daily growth of 9.39 μm.

[0055] Survival rate: The survival rate of the high-salt parent in a high-salt environment was 76.3%, and the survival rate of the low-salt parent in a high-salt environment was 69.26%.

[0056] Although the above embodiment provides a detailed description of the present invention, it is only a part of the embodiments of the present invention, not all of the embodiments. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. A method for cultivating high-salt-tolerant seedlings of Omi oysters, characterized in that: The following steps are involved: (1) collecting wild Crassostrea gigas parents and temporarily culturing them, during which the culture temperature is gradually increased from the natural water temperature to 24°C, and the salinity is gradually increased from 20‰ to 28‰; the temporary culturing comprises: a first temporary culturing stage, maintaining the salinity at 20‰ and gradually increasing the water temperature to 15°C; In the second temporary rearing stage, the salinity is gradually increased to 25‰ and the water temperature is increased to 18℃; In the third temporary rearing stage, the salinity is maintained at 25‰ and the water temperature is gradually increased to 24℃; In the fourth temporary rearing stage, the salinity is gradually increased to 28‰ and the water temperature is maintained at 24℃; (2) collecting sperm and eggs from mature gonadal parents, artificially inseminating them and incubating them in an environment with a salinity of 28‰. After the larvae develop into D-shaped larvae, the salinity is gradually increased to 30‰. After some larvae have eyespots, they are placed on a substrate; the temperature in the environment is 24-26°C. (3) After the larvae develop into juveniles with an average body length of 500 μm, they are cultured in a stress environment with a salinity of 35‰ and then transferred to normal seawater for cultivation.

2. The method for cultivating high-salt tolerant seedlings according to claim 1, wherein: The duration of the first temporary rearing stage, the second temporary rearing stage, the third temporary rearing stage and the fourth temporary rearing stage are all 7 to 10 days.

3. The method for cultivating high-salt tolerant seedlings according to claim 1, wherein: During each temporary rearing stage, the parents were moved to the pond once a day before the temperature exceeded 24°C, and the water was changed twice a day after 24°C, with the water exchange volume each time being 40-60% of the temporary rearing water.

4. The method for cultivating high-salt tolerant seedlings according to claim 1, wherein: During the temporary culture period of step (1), the feed includes diatoms, chlorella, golden algae and flat algae.

5. The method for cultivating high-salt tolerant seedlings according to claim 1, wherein: After the larvae in step (2) develop into D-type larvae, the salinity is gradually increased to 30‰ within 5 days.

6. The method for cultivating high-salt tolerant seedlings according to claim 1 or 5, characterized in that: The larvae culture density in step (2) is: after selection, the density is 5 to 6 per ml; after the shell length reaches 300 μm, the density is 1 to 2 per ml.

7. The method for cultivating high-salt tolerant seedlings according to claim 1, wherein: The time of the stress culture in step (3) is 96 hours.

8. The method for cultivating high-salt tolerant seedlings according to claim 1 or 7, characterized in that: In step (3), when the juvenile spat grows to 800-1000 μm, it is moved to a pond or natural sea area for temporary rearing, and then the spat is clamped or caged for rearing.

9. The method for cultivating high-salt tolerant seedlings according to claim 1, wherein: The change of salinity in step (1), step (2) or step (3) is achieved by changing water.