Collection and transportation of broodstock
The American redfish broodstock grows naturally in the United States mainly in the sea area. It is mainly cultured in ponds or cages in China, and fishing methods are mainly used for fishing. The broodstock must be trained for a certain period of time before they are shipped, so that they can adapt to the life in the barrel. Inflation can be carried out on short-distance transportation (within 5 hours). The long-distance transportation must be added with ice to keep the water temperature at about 21°C. Antibiotics can be added to the transfer water to reduce the risk of bacterial infection.
Hormones Induced Excretion of Redfish
Squeezing eggs can be done in smaller, cheaper tanks, which can synchronize the spawning season. However, squeezing eggs is more laborious and requires more solid technical expertise to keep normal fertilization in synchrony with ovulation. Broodstock may not tolerate artificial ovulation.
1. Estimation of broodstock maturity: Most of the broodstock that are caught during the spawning season (mid-August to mid-October) can be used for hormone-induced ovulation, but the development of gonads should be checked before hormone injection. For males, pressure can be applied on both sides of the fish and in the abdomen to extrude semen to check sperm production. For females, a 1-mm to 2-mm diameter glass tube can be inserted into the fallopian tube to obtain tissue samples in the ovary for microscopic examination. Mature eggs appear grayish yellow and egg diameter ≥ 0.5 mm.
2.Injection of hormones: Intramuscular injections of hormones can be performed when the eggs reach maturity. Human chorionic gonadotropin (HCG) of approximately 500 IU/kg-600 IU/kg fish weight can be administered within 24 hours to 30 hours at 25°C. Induction of ovulation (usually without injection of female fish), the addition of 1.0 mm to the egg during the final stage of maturation, becomes transparent, and produces 1 to 2 oil globules. When ovulation occurs, it is gently squeezed in the peritoneal cavity. Out of eggs. After the eggs and sperm are squeezed into a container, they can be fertilized. At the same time, a certain volume of seawater (salinity 28-32) is added, and it can be counted after one minute of stirring.
3. Post Spawning Procedure: The mixture of eggs and seawater is then transferred to a well-gassed 10 gallon aquarium for approximately 1 hour to 2 hours and then examined for meiosis. If 70% or more of the eggs undergo meiosis, eggs can be placed directly into the incubator. If the fertilization rate is 30%-70%, the inflating needs to be interrupted for a few minutes, live eggs will float on the water surface, and dead eggs will sink to the bottom, and the dead eggs will be removed by siphoning.
Incubation of redfish eggs and larvae
Redfish spawned buoyant, spherical, diameter of about 0.9 mm to 1.0 mm, eggs transparent, most eggs with a golden yellow oil ball.
Incubation usually takes place at 25°C up to 4 hours, and the vegetative organs are well developed after 48 hours of incubation. The optimal salinity for hatching is 28%-35%. The temperature should be maintained above 22°C, the ammonia concentration should be less than 0.5 mg per liter, and the dissolved oxygen should be higher than 3.0 mg per liter.
Growth and development of redfish larvae
Temperature is a relatively important environmental factor that affects growth. The ideal conditions for redfish eggs and larvae are 25°C-30°C, salinity 25-30. Increase 1 mm per day at the appropriate temperature for food intake and fish density. Therefore, juveniles developed from a newly hatched larvae to full scales are only weeks (3 weeks). Feeding of larvae was carried out 3 days after hatching. Five rotifers/ml were added at the beginning. Regardless of the fish density, they were fed 2 times to 3 times a day until the larvae reached 9 days to 10 days. At this time, Artemia was started. No nauplii, 1/mL in the first and second days, then halved, can not allow Artemia to increase in the aquarium, food changes after 15 days. At this time, some shrimp meal and commercial dry feed mix can be added while feeding on Artemia. After about 5 days, the Artemia supply can be stopped, and after 2 weeks to 3 weeks the shrimp can be slowly reduced and dry feed is used. Prepare fish to move into a water tank.
Harvest of red fry
Red fish hardened, more vulnerable to injury than other species, large fish fry smaller adaptability. The fish was harvested after approximately 30 days of stocking. Collect a few samples every week before harvesting with a harvesting box. Ensure good water quality and prevent low dissolved oxygen.
Transport and adaptation of red fry
There are two commonly used methods, the first is the canvas barrel transport, generally 1 cubic meter of barreled seedlings for 5000 - 10000 tail. The second is the transport of plastic bags (oxygenation), which is more commonly used domestically and has the highest survival rate. At this time, the seawater is first filled into the bag, and the fry are bagged and then filled with oxygen. After that, the bag is put into a foam plastic box. Generally, the fry is 2 cm-3 cm and 300-400 pieces per bag.
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