What are the key technical points for winter rearing of broodstock?

Broodstock rearing is divided into stages such as post-spawning care, autumn rearing, winter rearing and spring rearing. Because winter temperatures are low, broodstock activity decreases, their feeding ability is weaker and they are prone to fish diseases; if management is poor, it will have a great impact on the next year's artificial hatching, fry and fingerling production, market-size fish farming and other production stages. The key technical points for doing a good job of winter broodstock rearing are:

1. Pond selection

Broodstock ponds require an adequate water source, a flat pond bottom, shelter from wind and exposure to sun, and good water and heat retention, with an area of 10-15 mu being suitable.

2. Reasonable stocking

The stocking density of broodstock should be such that the water body is fully utilized while the gonads develop well; a reasonable stocking density is an important condition for ensuring successful broodstock rearing. The requirements for different species are:

For a pond mainly rearing silver carp broodstock, stock 10-15 brood fish weighing 5-8 kg each per mu, together with 3-5 bighead carp broodstock of the same size and 3-5 grass carp broodstock weighing about 10 kg each. For a pond mainly rearing bighead carp broodstock, stock 10-15 brood fish weighing 15-20 kg each per mu, together with 3-5 grass carp broodstock weighing about 10 kg each. For a pond mainly rearing grass carp broodstock, stock 15 grass carp broodstock weighing 8-10 kg each per mu, together with 3 silver carp or bighead carp broodstock and about 12 kg of Wuchang bream broodstock. The female-to-male ratio is generally 1:1.5, and at minimum no less than 1:1.

3. Daily management

Broodstock ponds must have a dedicated person responsible for careful management. Carry out frequent pond patrols, regularly add fresh water to increase dissolved oxygen, prevent seepage and maintain a certain water level so as to raise the water temperature. When the weather stays clear for consecutive days and the water temperature is above 6°C, feed appropriate amounts of concentrated feed and green feed for the fish to eat directly, so as to strengthen their constitution and reduce weight loss. For ponds mainly rearing silver carp and bighead carp, some fermented manure should be applied regularly throughout the overwintering period to raise the water temperature and fertilize the water quality.

4. Prevention and treatment of fish diseases

In winter, broodstock are prone to fish diseases such as saprolegniasis and white skin disease, so care should be taken to move quickly and gently when catching broodstock to avoid injuring the skin and scales of the fish; fish with relatively severe mechanical injuries should not be used as broodstock for the next year. To treat saprolegniasis, a 10-20 ppm bath in Weikang can be used, or Weikang can be splashed over the whole pond at 0.15-0.3 ppm.