Detailed Explanation of Key Techniques for Autumn Grass Carp Broodstock Rearing

In autumn and winter, the sex cells of grass carp broodstock are in the growth and development stage. The quality of feeding and management during this period directly affects the maturation of the gonads, the spawning induction results the following year, and the fertilization rate and hatching rate of the eggs. For this reason, the rearing of grass carp broodstock in autumn and winter should focus on the following points. 1. Pond preparation. The pond for rearing grass carp broodstock should be close to the spawning pond and have a good water source. The pond area is generally 3-4 mu, with a water depth of 1.5 m. Before stocking the broodstock, the pond should be cleaned and renovated, the pond embankments repaired, weeds removed, and the pond disinfected with quicklime or bleaching powder and other chemicals. 2. Broodstock stocking. The broodstock stocking time is generally best carried out between October and December. The broodstock used for breeding is best raised locally on site, but can also be caught from rivers, lakes, and reservoirs. The catching work is carried out in November and December, because the water temperature is lower at this time, and the broodstock is less likely to be injured during catching and transportation, with a high survival rate, and is also less likely to die after stocking. Earlier catching allows the broodstock a period of time to recover their physique, so that they can develop normally after the beginning of spring and catch up with the breeding season. Stocking density is very important. In ponds mainly for grass carp, stock 130-150 kg of grass carp broodstock per mu, that is, 12-15 grass carp broodstock weighing 7-10 kg each. In addition, stock 2-3 silver carp and bighead carp broodstock as a supplementary species. 3. Feeding and management. (1) Scientific feeding. In the earlier stage, green feed should be the main feed, combining green feed with concentrated feed. Green feed can include green grass, ryegrass, sweet potato vines, etc., and the amount fed depends on the feeding situation of the broodstock. Green feed can be fed up to 30% of the fish body weight at most, and concentrated feed at 1-2% of the fish body weight. As the temperature drops, green feed gradually becomes scarce, and the feed intake of grass carp broodstock gradually decreases. At this time, concentrated feed should be used entirely. The feeding method should be well controlled: on days with high water temperature, feed every other day; on days with low water temperature, feed once every 3 days. Concentrated feed should be placed on feeding tables, and the feeding tables should be built on the bottom near the shore; green feed should be put into baskets, and the grass baskets should be moved regularly to remove sunken rotten grass. (2) Keep the water quality fresh and clean, and regularly add new water, generally once every 15-30 days. (3) Disease prevention and treatment. In autumn and winter, grass carp broodstock is prone to enteritis, water mold, gill rot, and other diseases. Once fish disease is found, it should be diagnosed promptly and treated according to the symptoms. Each month, an appropriate amount of quicklime and bleaching powder solution can be splashed into the pond, which can play a role in disease prevention.