Detailed Explanation of Key Techniques for Broodstock Breeding in Icefish Aquaculture

1. Source of broodstock.

Sexually mature individuals caught during the breeding season of large icefish can be used for artificial breeding; individuals raised to sexual maturity can be used for artificial breeding; individuals that have not reached sexual maturity must not be used for artificial breeding.

2. Capture of broodstock.

The capture of large icefish should be carried out during the peak spawning period; in areas north of the Yellow River, capture can begin in early December, and in areas south of the Yellow River, capture can begin in mid-December. The capture nets can be gill nets (mesh size 2a of 1.5-2.4 cm) or under-ice seine nets. Broodstock should be caught at spawning grounds where spawning and reproduction are relatively concentrated; when removing fish from gill nets, they should be gently taken off head-first.

3. Rearing of broodstock.

Individuals caught during the concentrated fishing period of large icefish that are robust in constitution, large in size, and whose gonads are not yet mature can be used for broodstock rearing, and shall comply with the following provisions:

(1) Broodstock can be reared in cages or ponds.

(2) The specifications of broodstock rearing cages can be 5 m x 5 m x 2 m, or 4 m x 4 m x 1.5 m, with a mesh size 2a of 0.5 cm; the area of broodstock rearing ponds can be 0.2-0.4 hectares, with a water depth of 1.5 m.

(3) The rearing density in cages should not exceed 4000 fish/cubic meter, and the rearing density in ponds should not exceed 0.5 kg/cubic meter.

(4) For the rearing period, sufficient small fish and shrimp should be provided for the broodstock to feed on, and rearing management should be strengthened.

4. Selection of broodstock.

Signs of maturity in female fish: large in size and robust in constitution, abdomen obviously enlarged, anal fin relatively small and triangular in shape, after lifting the fish body egg grains can be seen flowing in the abdomen, the abdomen feels soft to the touch, and lightly pressing the abdomen causes egg grains to flow out; the eggs are round, bright, and scattered. Signs of maturity in male broodstock: the individual is smaller than the female broodstock, the abdomen is not swollen, the chest of the mature male is rose-red, the anal fin is wavy and curved, the scales above the anal fin are large and have adhesive force, and on the left side of the body cavity above the vent there is a crescent-shaped, milky-white testis.