CATDOLL : CATDOLL: What should we pay attention to in the breeding technology of yellow croaker fry?

1. Broodstock selection

There is no obvious difference between male and female large yellow croaker, and males mature early. It is best to choose those that are more than 2 winters old, with bright colors and good vitality.

Intensive cultivation and ripening of broodstock: When the water temperature is below 15℃, move them to the wintering grounds, where the water temperature is 16±1℃, and raise male and female broodstock together. From March to April, select some broodstock for intensive cultivation and feed them with small fresh animal baits. Use drugs to ripen them regularly in spring and winter.

Select artificially cultured adult fish that are over 2 years old, weigh more than 500g, and are strong and uninjured for intensive cultivation. Put the selected broodstock in a net cage, feed them mainly with high-quality, fresh small fish, supplemented with compound feed, and add 1-2% fish vitamins. In winter, when the seawater temperature is low, move the broodstock into an indoor cement pool, feed them with high-nutrition baits such as oysters and sandworms, and keep the water fresh to make the broodstock have a strong appetite. During this period, extend the light time, increase the temperature, and use hormones to accelerate the development of the broodstock gonads.

2. Artificial seedling cultivation

Artificial induction of labor: The abdomen of female fish is swollen and soft, while that of male fish is soft and contains semen when lightly squeezed. The oxytocin is made from carp pituitary gland, LRH-A, DOM+SGARH, used alone or in combination, and injected once. The injection site is at the base of the pectoral fin without scales. The injection time is between 10 am and 12 pm.

Spawning and fertilization: Use fresh filtered seawater, pre-aerate, and stimulate the spawning process with appropriate water flow; swim slowly before estrus, and enter the proestrus after 30 hours. Male fish like to swim constantly in the upper and lower layers of the water, while female fish swim slowly, and the reproductive pores are red and protruding; after 35 hours, the parents begin to estrus, chasing each other in groups, and "cooing" sounds can be heard. Estrus lasts for 2 to 3 hours and reaches a climax, continuing until after midnight, and then enters the spawning stage. During spawning, the female fish produces misty light yellow fine-grained eggs, and the male fish lies on its side and discharges semen.

Fertilized egg collection: egg diameter 1150 ~ 365um, oil ball about 319.8um, floating eggs; collected using 80 mesh cage flow method or scooping method.

Transportation of fertilized eggs: Use 30L film bags and 10L seawater for oxygenation, and then pack them in foam boxes for transportation. Generally, long-distance transportation is by air and truck, and short-distance transportation is by truck.

After April, the gonads of the broodstock gradually mature. When the gonad maturity index (GS1) reaches 20%, artificial induction of spawning can be performed. Eugenol anesthesia is applied before induction of spawning, and the LRH-A3 injection dose is 50-100. The naturally fertilized eggs produced in the pond are collected by running water or sieve silk and moved to the nursery pond for incubation. Under the condition of 18-4℃, the incubation process takes about 27-42 hours.

During the spawning season, broodstock that can squeeze out mature eggs and semen are collected at the Guanjingyang spawning grounds for artificial insemination on site. Fertilized eggs are separated and transported back to the nursery room for screening again before being put into the pond for hatching. In addition, broodstock that are strong and healthy, with a swollen and soft abdomen of females, clear ovarian contours, and males that can squeeze out thick semen are selected from artificially cultivated broodstock. After being anesthetized with eugenol, hormones of different dosage forms and doses are injected. Then, they are placed in the spawning pond at a ratio of 1:1 between males and females, continuously aerated, and flushed regularly to stimulate the broodstock to spawn naturally. Fertilized eggs are collected by the running water egg collection method or the egg scooping method, and are counted and put into the incubator or pond after screening.

3. Seedling cultivation

Control of environmental factors: Water temperature 10-32℃, optimum water temperature 20-28℃, salinity 20‰-32‰. Too low salinity can easily cause deformities. Sudden changes in light will cause fish to become restless, jump in large numbers, float up the fry, and go into shock and die. Fry are apt to survive in weak light, so light intensity should be controlled at less than 2000Lx. Fish are particularly sensitive to light in the later stages, so it should be controlled within 500-800Lx.

Water quality conditions: Use still water or flowing water for cultivation. In the early stage, use still water, and change 1/5 to 1/4 of the water a day. In the later stage, use intermittent flowing water to cultivate fry, twice a day. Later, the amount of flowing water will be increased. Generally, feed is fed in still water for 2 to 3 hours before flowing water. Ammonia nitrogen <0.3ppm, pH is 7.8 to 8.5, and dissolved oxygen is one air stone/2m2.

The density of larvae and juveniles culture is: 30,000 to 50,000/m3 of water body in the larval stage, 10,000 to 30,000/m3 of water body in the juvenile stage, and 5,000/m3 of water body in the young fish stage. After the scales of young fish have fully grown, they are moved to the sea area for cage culture.

Cultivating seedlings in earthen ponds: After 2-3 days of feeding on Artemia, move them into earthen ponds for further cultivation. The earthen ponds should be cleaned in advance and fertilized. Compared with indoor cultivation, seedlings in earthen ponds grow faster and have better vitality. Their body color is brighter.

The cages for juvenile and young yellow croaker should be set up in the harbor, where the tide is not urgent but smooth, the flow direction is stable, the flow rate is less than 1 meter per second, there is "reciprocating flow", but avoid "vortex flow" in the sea area. The water depth of the harbor area is required to be more than 5 meters. Even at the lowest tide, it is necessary to ensure that the bottom of the cage is more than 1.5 meters away from the seabed; it is best to have mountains or large reefs around the harbor area to block the wind and prevent wind and waves. Cultivate the fish in the pond into juvenile fish with a total length of more than 30 mm. Generally, in a small indoor cement pool with a volume of 20 to 30 cubic meters, the cultivation density is 30,000 to 50,000 per cubic meter of water. All newly built cement pools must be thoroughly soaked for 1.5 to 2 months before they can be used.

1. Selection of broodstock: The difference between male and female yellow croaker is not obvious, and males mature early. It is best to choose those that are more than 2 winters old, brightly colored, and have good vitality. Strengthening and ripening of broodstock: When the water temperature is below 15℃, move them to the wintering ground, the water temperature is 16±1℃, and male and female are mixed; from March to April, select some broodstock for intensive cultivation, feed small fresh...

2. Artificial breeding and artificial induction of labor: The abdomen of the female fish is swollen and soft, while the abdomen of the male fish is soft and contains semen when lightly squeezed. The oxytocin is made from carp pituitary gland, LRH-A, DOM+SGARH

During the cultivation process, we must pay attention to the germination time of the seedlings, and also pay attention to the need for the cultivation process to be moist and maintain a good temperature.