A brief analysis of the large-scale breeding technology of blunt-nosed yellow-covered flounder

A brief analysis of the large-scale breeding technology of blunt-nosed yellow-covered flounder

Zheng Chunbo

Pseudopleuronectes yokohamae, belonging to the flounder family, flounder family, yellow lid flounder genus, commonly known as yellow lid, sand board, small beak, small high eye, is a shallow sea small fish. It is mainly distributed in the sediment bottom or reef bottom sea near the northwest pacific ocean, and is distributed in the northern part of the East China Sea to the Yellow and Bohai Seas, the Korean Peninsula, the Tatar Strait of Russia and the southern part of Hokkaido, Japan. Blunt-nosed yellow flounder is a cold and warm demersal fish, mostly living in the seabed for argy, sandy bottom area, its migration range is small, adaptable, low temperature resistance, is an ideal species for marine aquaculture. Its tender flesh, high nutritional value, popular with domestic and foreign consumers, is a very important marine economic fish resources, but also one of the main flounder fish catches in China's Yellow Bohai Sea. In 2017, the authors conducted a study of the large-scale breeding technology of blunt-nosed yellow flounder and achieved good results, and the trial status is reported as follows. [Yoshiyama Huayao self-media network debut]

1 Test conditions

1.1 Test site

Nursery in Weihai Wenden District Haihe Aquatic Nursery Co., Ltd.

1.2 Cultivation of water bodies

The use of effective nursery water body 544 m 3, a total of 34 nursery ponds, nursery pond size specifications are the same, single pond seedling water body 16 m 3 (specification of 4 m×4 m×1 m); the bottom of the pool is a pot bottom type; in the lowest part of the pool is provided with a drainage hole, pore diameter of 110 mm; in the upper part of the pool set up 2 water holes, controlled by valves, pore size of 30 mm, the size of the flow can be adjusted as needed.

1.3 Water source and water quality conditions

The water for seedlings is taken from the underground seawater of the seawater well (well depth of 25 to 30 m) by an electric pump, filtered by the sand filter tank and entered into the pool. The underground seawater is transparent and clear, does not contain harmful heavy metal ions, and the sulfide < 0.02 mg/L, and the water quality meets the national fishery secondary water quality standards. The annual temperature of well water is 14~23 °C, salinity is 25~32, and pH is 7.6~8.5.

1.4 Aeration facilities

The aeration of the nursery pond uses aerocarburium. With the Roots blower as the main engine, the main pipe is made of PVC hard pipe, and each nursery pond is connected with a polyethylene hose to connect the gas stone, and 16 gasstones are evenly placed at the bottom of each pool to continuously inflate.

1.5 Illumination

In the center above the nursery pond, install a 20 W energy-saving lamp with a light of 500~1 500 lx.

2 Test methods

2.1 Sources and selection of broodstock

The blunt-nosed yellow flounder broodstock used in the test are derived from wild broodstock caught off the coast of Shuangdao Bay in Weihai City. From March 7 to 10, 2017, a total of 131 broodstock were harvested, of which 102 were females with body mass of 483-825 g/tail and an average body mass of 662 g/tail; males had 29 fish with a body mass of 338-506 g/tail and an average body mass of 428 g/tail; and the ratio of males to females was 3.5: 1.

The blunt-snouted yellow-covered flounder, which has obvious selective gonadal development, no damage to the body surface, and no disease, acts as a broodstock. Broodstock are transported at a water temperature of 8 °C and a density of 15 to 20 fish/m3. After the broodstock are transported back, a medicinal bath of povidone iodine liquid with a mass concentration of 30 mg/L is used for 3 to 5 minutes.

2.2 Intensive rearing of broodstock

Broodstock were reared in 2 cement ponds indoors, with a bottom area of 16 m2, using normal flowing water, the amount of flowing water was 4 to 5 full/d, and the average cultivation density was 4.1 tails/m2. Broodstock are bred to promote ripening by using three measures: temperature control, light control and increased nutrition. The water temperature is controlled at 9 ~10 °C, and the light is 100~150 lx. The bait for raising broodstock is live sand silkworms, fresh fish such as jade tendon fish, anchovies, etc., and add an appropriate amount of vitamin C, vitamin E, cracked pot algae powder and other nutrients to the feed fish, and the amount of bait is 1% to 3% of the body mass of the fish per day. Gonadal development is observed and checked frequently.

2.2 Acquisition of fertilized eggs

2.2.1 Natural spawning to obtain fertilized eggs Select broodstock with mature gonadal development, concentrate on the spawning pool, adopt flowing water, temperature control, and light control methods, so that mature broodstock naturally spawn and ovulate, and the eggs laid into the pool are naturally fertilized, and the fertilized eggs are collected in the cage with the flowing water, and the fertilized eggs in the cage reach a certain density and are taken out for later use.

2.2.2 Artificial squeeze to obtain fertilized eggs Select the female fish with an enlarged abdomen, gently squeeze the abdomen to squeeze the mature eggs into a clean container prepared in advance, and then select the male fish with mature gonadal development, gently press the abdomen to flow out the mature milky white semen, suck the semen out with a straw, drip into the container containing the eggs, slowly inject a certain amount of clean seawater, gently stir with a glass rod, so that the eggs and semen are fully mixed and evenly fertilized, and after 4 to 5 minutes, wash off the excess semen and impurities with clean seawater.

After obtaining the fertilized eggs, they are soaked with a mass concentration of 15 mg/L of povidone iodine solution for 3 to 5 minutes, then rinsed with clean seawater, the dead eggs are selected, and then counted and placed in a prepared cage for incubation.

2.3 Incubation

Incubate in cages placed in incubation tanks (water depth 1 m). The cage is sewn with 60 mesh polyethylene sieve mesh with a size of 1 m×1 m×0.6 m, the cage is suspended in the incubation tank, and the incubator is suspended with an attachment base made of 40 mesh 0.4 m × 0.4 m×0.4 m screen silk mesh, and the eggs are attached to the attachment base. The density of the attachment base eggs is 15,000 to 20,000 grains/m2.

During incubation, the mucus in the incubator and the dead eggs at the bottom of the cage are removed in time, and the development progress of the fertilized eggs is examined daily, and the water is changed regularly.

Incubation adopts micro-flowing water, micro-inflation, light control and temperature control methods for incubation. Incubation conditions: light 500~1 000 lx, water temperature 11~13 °C, salinity 30, pH 7.8~8.5, dissolved oxygen >6 mg/L.

2.4 Rearing of juvenile, juvenile and juvenile fish

At water temperature 11 to 13 °C, the baby fish burst out of the membrane after 9 days of fertilized eggs. After hatching, stop the air for 5 to 10 minutes, and then count the healthy hatched fish floating, and move the water into the nursery pond for cultivation.

2.4.1 Rearing density of juvenile fish and juvenile fish: 0.8 million to 10,000 juvenile fish/m3, juvenile fish 0.5 million to 0.8 million/m3.

Feeding: The hatching of the juvenile fish is 2 to 5 days, the total length of the juvenile fish is about 4.8 mm, the density of concentrated chlorella in the breeding pond is 200,000 to 300,000 cells /mL, and the rotifers are fed with chlorella and cracker algae (rich in DHA and EPA) for more than 24 hours, and the rotifer density is 3 to 5 / mL, feeding twice a day. Hatched 6 to 12 d, the total length of the calves is about 6.6 mm, the swimming ability of the juvenile fish is enhanced, concentrated in the middle and upper layers of the pond water, the density of chlorella in the breeding pond is maintained at 200,000 to 300,000 cells / mL, and the density of rotifers is 8 to 10 / mL, fed twice a day. The hatching of the calves was 13 to 23 d, the total length of the fry was about 8.6 mm, and the euphorbia began to be cast into the euphorbia, the feeding density was 1 to 3 mL, and the feeding density of the rotifers and the density of chlorella gradually decreased, and the domestication and feeding of the compound feed began to be fed 3 times/d, at this time, it has developed to the juvenile stage. Hatched 24 to 26 d, fry length of about 10 mm, began to metamorphose, the left eye moved up, after 3 to 4 d metamorphosis completed, into the juvenile stage, feeding to the compound feed, a small amount of feeding of harvest insects avalve, feeding 4 to 6 times / day. The specific amount of bait at each stage should also be appropriately adjusted according to the amount of residual bait in the breeding pond and the degree of gastrointestinal fullness of the baby fish and juvenile fish.

Water change, sewage suction: the second day after the opening of the fish began to change the water, change the water 1 time / d, the water change rate is 10% to 15% per day; 6 ~ 12 d, suction 1 time / d, start to flow, the flow rate is 50% to 75% per day; 13 ~ 23 d, increase the amount of water flow, absorb pollution 1 time / d, the flow rate is 80% to 100% per day; 24 ~ 25 d, the amount of water increases, the water absorption is 1 time / d, the flow rate is 100% to 150% per day. Sewage suction is carried out after each baiting is completed, and the siphon method is used to suck up the dirt and residual bait at the bottom of the pool.

Water temperature: 2~ 5 d, gradually heated to 13 °C, hatched 6 ~ 12 d, the water temperature of the breeding was controlled at 13 ~ 15 °C; the hatching of the 13 ~ 23 d, the cultivation water temperature was controlled at 15 ~ 16 °C; the water temperature of the hatched fish was controlled at about 17 °C after hatching for 24 days.

Inflation: Continuous micro-inflation using a Roots blower to microwave the water surface.

Illumination: Controlled at 500~1 500 lx.

2.4.2 Rearing density of juvenile fish: total length 20~30 mm, density 0.5 million~0.3 million/m2, total length 30~40 mm, density 0.25 million~0.2 million/m2, full length 40 mm density of 0.2 million~0.15 million/m2.

Feeding: Juveniles look similar to adults, with juveniles completely lying down. Juveniles can swim from the bottom of the pond to the upper layer of the water in groups to grab food, at which time the amount of food is greatly increased and the growth is rapid. The feed is artificial compound feed, and the bait is 3 to 4 times per day. The specific amount of bait should be appropriately adjusted according to the amount of residual bait in the breeding pond and the fullness of the stomach of the juvenile fish.

Water change, sewage: the hatching of the fish 27 ~ 39 d, sewage 3 times / d, the use of normal flow of water cultivation method, the flow rate of 150% to 200% per day; after the hatching of the fish 40 d, the amount of water increased, the flow rate of 300% to 400% per day, sewage 3 times / d, after the completion of each bait.

Pond and screening: When the total length of juvenile fish reaches about 20 mm, the pool is screened once, and the total length of juvenile fish reaches about 30 mm, and the whole length of the juvenile fish reaches about 30 mm, and the whole length of the juvenile fish reaches about 40 mm, and the pool is screened once. The specific situation should be determined according to the density of juvenile fish distributed at the bottom of the pond, and excessive density affects the growth rate and the survival rate. When screening ponds, the method of fishing nets is used for drainage, and then the method of manual picking is used to separate the small and large juvenile fish, and the juvenile fish with similar individual size are concentrated in the same pond for breeding.

Water temperature: 15~17 °C;

Inflation: continuous inflation, increased gas volume;

Illumination: 500~1 500 lx.

Juvenile fish out of the pond: When the juvenile fish have a total length of > 50 mm, they can be sold out of the pond for indoor grow-out or artificial breeding and stocking.

2.5 Disease control

The prevention and control of diseases adheres to the principle of "prevention as the mainstay, prevention and control combined", pays close attention to the feeding, activities, growth of juvenile fish and whether there is any abnormality in the water quality in the breeding pond in the daily management, and timely detects the precursors of the disease and takes corresponding measures to solve it.

2.5.1 Maintain a good water environment Fry in different periods should take different amounts of water replacement (flowing water) according to their growth needs, especially in the juvenile stage, the amount of water flow should be increased. After the bait is thrown, the feces and remaining bait at the bottom of the pond should be cleaned up in time to maintain a good water environment.

2.5.2 Ensure that the bait is of good quality and sufficient amount The rotifers fed must undergo nutritional fortification of chlorella and chlorella and chysophorus phylloxera for more than 24 h; the euphorbia of the harvesters must not carry the egg shells of the harvest insects.

2.5.3 Timely separation and transfer of ponds With the continuous growth of juvenile fish and juvenile fish, it is necessary to divide and move ponds in a timely manner according to the situation to reduce the cultivation density of juvenile fish and juvenile fish, improve the ecological environment, promote growth, and improve the survival rate of breeding.

3 Results

From the acquisition of broodstock on March 7, 2017, to August 14, 2017, a total of 523,000 juveniles with an average total length of 52.7 mm, normal morphological color and healthy and lively juveniles were bred.

4 Summary

Through the experiment, the problem of inability to obtain batch fertilized eggs in a concentrated manner due to the unsynchronized development of male and female broodstock broodstock was solved; the problem of low hatching rate of sticky fertilized eggs of blunt-nosed yellow-covered flounder due to long incubation time was solved; and the problem of demand and conversion of palatable bait at different stages of development of blunt-nosed yellow-covered flounder, juvenile fish and juvenile fish was solved.

The smooth implementation of the project has laid a solid foundation for the development of the aquaculture industry of blunt-nosed yellow-covered flounder, and provided strong technical support for the resource restoration of blunt-snouted yellow-covered flounder.