Key points for autumn and winter rearing techniques of black carp, grass carp, silver carp and bighead carp broodstock

Broodstock rearing is an important part of the artificial propagation of black carp, grass carp, silver carp and bighead carp. The feeding and management work in autumn and winter directly affects the induced spawning results of the following year, so it must be given full attention.

1. Conditions and clearing of the broodstock pond.

The pond for rearing broodstock should not only be close to the spawning pond but also have good water source conditions, and be convenient for irrigation and drainage. The pond bottom should have little mud; for silver carp and bighead carp ponds, a mud depth of 20 cm is sufficient, while black carp and grass carp ponds should contain little or no mud. The area should be 2000-3300 sq m, with a water depth of about 1.5 m. The broodstock rearing pond must be cleaned and prepared before stocking: remove excess mud, repair the pond embankments, cut away weeds, and thoroughly clear the pond with quicklime or bleaching powder and other drugs.

2. Stocking of broodstock.

(1) Time: Stocking of broodstock is best completed before the end of October, and at the latest no later than February of the following year. The broodstock used for propagation is best reared on site, but can also be collected from rivers, lakes, reservoirs and other waters. Collection can be carried out in November-December together with adult fish harvesting, because at this time the water temperature is lower, and the broodstock is less likely to be injured during capture and transport, the survival rate is higher, and they are less likely to die after stocking. In addition, earlier capture allows a longer period for recovery of body condition, so that after the beginning of spring they can develop normally and be ready for propagation.

(2) Density: A reasonable stocking density is an important condition for good broodstock rearing. In ponds mainly for silver carp and bighead carp, stock about 100-150 kg per mu. In ponds mainly for silver carp, stock 16-20 silver carp of 6-8 kg each, with 2-3 bighead carp of 10 kg each and 2-3 grass carp as secondary species. In ponds mainly for bighead carp, generally do not stock silver carp, so as to avoid silver carp affecting bighead carp; stock 4-6 grass carp of 6-8 kg each per mu. The female-to-male ratio of silver carp and bighead carp broodstock is generally best at 1:1.5; if there are fewer males, the ratio can be slightly lower, but not lower than 1:1. In silver carp and bighead carp broodstock ponds, no @#@233@#@ species should be interstocked, so as not to affect the gonadal development of the broodstock. In ponds mainly for grass carp, the stocking amount is about 130-150 kg per mu, that is, 12-15 grass carp of 7-10 kg each, with 2-3 silver carp or bighead carp broodstock as secondary species. In ponds mainly for black carp, the stocking amount is 160-200 kg per mu, that is, 8-10 black carp of 15-20 kg each. The female-to-male ratio of black carp and grass carp broodstock is best at 1:1.5.

3. Feeding and management of broodstock.

(1) Silver carp and bighead carp: Silver carp and bighead carp mainly feed on plankton, so fertilizer should be applied appropriately to cultivate plankton. Autumn fertilization is the key to rearing silver carp and bighead carp broodstock well; water quality must be well controlled to ensure the pond water is "fertile" and "fresh". Generally, before stocking the broodstock, apply 500-750 kg of organic fertilizer per mu as a base fertilizer, and afterward carry out supplementary fertilization according to the principles of applying little but often and fertilizing according to water conditions. In principle, apply 350-400 kg each month. After winter begins, fertilizer should also be applied as appropriate to ensure the water color does not become clear in winter. In clear and warm winter weather, feed concentrated feed such as soybean cake and soybean milk. At this stage, new water should also be added appropriately according to conditions to regulate water quality, mainly with green feed, combining green and concentrated feed: regular water addition is the key to rearing grass carp well. At this time, the green feed for grass carp can use green grass, ryegrass, sweet potato vines, etc. Concentrated feed can use large @#@245@#@, malt, soybean cake, etc.: the feeding amount depends on the feeding situation of the broodstock; green feed can be fed up to 30% of the fish body weight, and concentrated feed at 1%-2% of the fish body weight. As the temperature drops, green feed gradually becomes exhausted, and the feeding intensity of grass carp decreases; at this time, only concentrated feed should be used: in weather with high water temperature, feed every other day, and when the water temperature is low, feed once every 5 days, and continue feeding this way until the broodstock stop feeding for overwintering. Concentrated feed should be placed on feeding platforms; the feeding platform should be built on the pond bottom relatively close to the bank, and the feeding platform should be cleaned and tidied regularly; green feed should be put into grass baskets, and the grass baskets should be moved regularly to remove sunken rotten grass. At this stage, water should also be added regularly to keep the water quality fresh; generally, add water once every half month to one month.

(2) Black carp: At this stage, black carp broodstock should mainly be fed snails and clams, and when the quantity is insufficient, concentrated feed such as soybean cake should be used as a supplement. Snails, clams, etc. should be evenly scattered on flat pond shallows with a water depth of 0.6-1 m and 2-3 m from the pond bank; the feeding amount depends on the feeding situation, with satiation as the standard. It is necessary to ensure a year-round supply of snails and clams at 20 times the fish body weight and an appropriate amount of concentrated feed, so as to ensure the gonadal maturity of the broodstock. Black carp ponds also need fresh water quality, so new water should also be added regularly to promote the appetite and gonadal development of the black carp, but the number of water additions can be slightly less than for grass carp.