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(A) broodstock
1. The source of the broodstock.
Sexually mature individuals caught in the breeding season of large silverfish can be used for artificial propagation; individuals that are stocked until sexual maturity can be used for artificial propagation; individuals that are not mature enough to perform artificial breeding can not be used.
2. Broodstock fishing.
Fishing for silverfish should be carried out during the spawning period. The area north of the Yellow River can be harvested from the beginning of December and the area south of the Yellow River from the middle of December. Fishing nets can be gilled (1.5-2.4 cm mesh 2a) or ice-pulled. The broodstock should be caught in spawning sites where spawning is more concentrated; when picking fish on the gill net, they should be gently inverted from the head.
3. The stocking of broodstock.
During the period of centralized fishing of large whitebait, the physique captured is strong and individuals are large. However, individuals whose gonads are not yet mature may carry out broodstock stocking and shall meet the following requirements:
(1) Broodstock can be stocked in cages or ponds.
(2) The size of the broodstock storage cage may be 5m 5m 2m, or 4m 4m 1.5m, mesh 2a 0.5 cm, and broodstock ponds may be 0.2-0.4 hectares , water depth 1.5 meters.
(3) The cage stocking density should not exceed 4,000 m/m3 and the stocking density of the pond should not exceed 0.5 kg/m3.
(4) During the period of stocking, a sufficient amount of small fish and shrimp should be used for broodstock consumption, and the management of stock raising should be strengthened.
4. The choice of broodstock.
Signs of maturity of females: They are generally healthy. The abdomen is obviously shaped and the anal fin is smaller. It is triangular. After the fish is lifted up, it can be seen that the abdomen has egg flow, the hands touch the abdomen is soft, and the abdomen has ooze out of the egg, oval, bright And scattered. The mature flag of the male broodstock: the individual is smaller than the female broodstock, the abdomen does not inflate, the mature male has a rose-red chest, an anal fins, a large scale above the anal fins, and an adsorption force. The left upper body cavity of the excretory hole has a crescent-shaped and Milky testis.
(II) Artificial insemination
1. Sex ratio.
The proportion of male and female broodstock used for artificial reproduction is 1:2-3.
2. Insemination method.
Dry insemination should be used. The specific method of operation is as follows.
(1) Semen insemination. Gently pinch the female head with her left thumb and forefinger. Lift the female with a dry cloth and dry the fish with a dry cloth. Gently squeeze the female abdomen with the right thumb from top to bottom to allow the eggs to flow into the dry seeding dish. Take 2-3 males in sequence to dry the body surface, squeeze the semen in the anal fin area, and put it into the fertilization dish to be inseminated along with the fish body, and immediately add a small amount of sieve water filtered reservoir water or 0.7% Saline, shake for 1 to 2 minutes.
(2) Testis insemination. Use a pointed tweezers to pierce the male abdomen forward from the anus, pick the intestines, pick the testes in a dry seeding dish, grind the testes with a glass rod or tweezers, and then pull the female head up and down, from front to back Gently squeeze the abdomen, make the eggs flow into the dish to be taught, stir the sperm and eggs with the caudal fins of the male fish, and then add a small amount of filtered reservoir water or 0.7% physiological saline, and shake for 1-2 minutes.
(C) Fertilized eggs hatching The fertilized eggs of the big whitebait should be hatched at a low temperature. The hatching time is relatively long, and it is hatched until the mid-term of the original intestine that can be transported and put in. The average water temperature is 6°C-7°C and it takes more than 100 hours. It takes about 30 days to hatch into fry. If the water temperature is lower, the incubation time is longer, so the change of water temperature must be controlled throughout the incubation process. Meet the requirement of dissolved oxygen for the development of fertilized eggs to prevent the emergence and spread of fertilized eggs.
The water temperature is controlled within 1°C-8°C, and water can not be frozen or exceed 10°C, otherwise it will greatly reduce the hatching rate or developmental deformity. The sudden change of water temperature should be controlled within 2°C. When the water is changed, the reservoir water with the same temperature can be used to change the water. The dissolved oxygen is achieved by changing the water. Generally, the number of daily water changes is determined according to the water temperature, and the average value within 3 days starts. Water temperature is about 3 °C, or do not move the hatchery as well, after the incubation process, the average daily water temperature is lower than 4 °C, 2 days for a water, such as the average daily water temperature 5 °C - 8 °C, usually one day for water 1-2 times. The fertilized eggs cannot overlap in the hatchery tray. Otherwise, they will die of hypoxia or developmental malformations. The water depth of the hatching plate is about 5 cm. The hatching room should not be exposed to direct sunlight or dark rooms.
In the method of artificial reproduction of whitebait, the new whitebait of Taihu Lake is basically the same as the big whitebait, but the breeding season is different. The following describes the artificial breeding of whitebait with large silverfish as an example.