Key Technical Points for Spring Broodstock Conditioning of the Four Major Chinese Carps

Spring is an important period for the maturation of broodstock gonads. From the beginning of spring to spawning, a large amount of nutrients in the broodstock's body is diverted to gonad development, so broodstock conditioning should be intensified in spring to meet the needs of gonad development, promote timely maturation of broodstock and ensure smooth spawning. The conditioning techniques are:

1. Divide ponds early. Adjusting stocking density and species combination is the primary condition for good broodstock conditioning. The pond area for broodstock division should preferably be 2000-2600 sq m. Before dividing the ponds, first drain the pond water, remove wild trash fish, snails, mussels and harmful organisms, and at the same time remove part of the sludge, then spread 100-150 kg of quicklime per mu for disinfection. After 5 days, fill with water to a depth of 1 m; for silver carp and bighead carp broodstock, apply 200-300 kg of fermented pig manure per mu as base fertilizer, and the stocking density should preferably be 150-200 kg per mu. Broodstock ponds should not be used for polyculture of fingerlings and market fish. If the ponds were already divided at suitable density in the previous autumn, they need not be divided again in spring. For such ponds, one-third of the pond water can be drained, keeping the water depth at 0.8-1 m, and the water can be sunned for about 10 days, which can raise the pond water temperature and promote early feeding of the broodstock.

2. Apply bait and fertilizer early. After overwintering for as long as 150 days, the nutrients stored in the broodstock's body have been largely consumed and their constitution is relatively weak. At this time, whether nutrition can be fully supplied will directly affect the gonad development of the fish. Applying bait and fertilizer early can meet the nutritional needs of the broodstock, promote gonad development, increase egg-carrying capacity, and enable timely entry into the smooth-spawning period. When the water temperature reaches 6-8 degrees C, silver carp and bighead carp broodstock ponds should promptly be fertilized to promote the reproduction and growth of food organisms, and additional fertilizer should be applied in good time according to water color. After the water temperature reaches 12-15 degrees C, fertilization should follow the "three observations," namely "observe water color, observe weather, observe fish activity," and should be applied in small amounts many times. The transparency of the pond water should be kept at 25-30 cm. Silver carp and bighead carp broodstock are mainly conditioned with fertile water, and each broodstock should also be fed about 20 g of concentrated feed per day, such as wheat bran, cornmeal and soybean cake powder in equal thirds. For grass carp broodstock in the early conditioning stage, feed 1 cm-long malt at 25 g dry weight per fish per day, and also feed vegetable leaves and aquatic plants; in the later stage, mainly feed grass, giving as much as they will eat, with the criterion that it is finished within 3-4 hours.

3. Add water at the right time. Ensuring good water quality is the key to broodstock conditioning. Flushing more water and frequently can regulate pond water quality, improve the pond water environment, and promote earlier maturation of broodstock gonads. Starting from a water temperature of 10 degrees C, flush and add water once a day, raising the water level by 3-5 cm each time; silver carp and bighead carp broodstock ponds should be flushed once a week. In the half month before spawning, grass carp ponds should be flushed once a day for 2 hours each time, while silver carp and bighead carp ponds should be flushed once every 2-3 days; after reaching the highest water level, new water should be pumped in to replace the old.