CATDOLL : CATDOLL: Production technology and breeding methods of the four major carps

1. Strictly select the natural original species of broodstock, which should be healthy and have well-developed gonads. The individual weight of silver carp should be above 6Kg, bighead carp should be above 10Kg, black carp should be above 15Kg, and grass carp should be above 8Kg. The annual renewal rate of broodstock should be about 10%.

2. Scientifically clean the fish pond. The broodstock pond should be easy to irrigate and drain. The bottom of the silver carp and bighead carp pond should have 20 cm of silt, while the bottom of the silver carp and grass carp pond should contain little or no silt. The area should be 1-5 mu and the water depth should be about 1.5 meters. The pond should be cleaned before stocking.

3. Reasonable combination: For ponds mainly stocked with silver carp, 3-4 bighead carp and grass carp should be stocked per mu; for ponds mainly stocked with bighead carp, 6-8 grass carp should be stocked per mu; for ponds mainly stocked with black carp, 2-3 silver carp and grass carp should be stocked per mu; for ponds mainly stocked with grass carp, 3-5 silver carp or bighead carp should be stocked per mu. The male-female ratio of silver carp, bighead carp, black carp and grass carp broodstock should generally be 1:1-1.5. At the same time, 8-10 mandarin fish and about 150 silver carp should be stocked per mu to control the breeding of wild fish and large zooplankton.

4. Strengthen feeding management Before stocking, 500-700 kg of decomposed organic fertilizer should be put into the silver carp and bighead carp broodstock pond per mu to cultivate plankton, and appropriate fertilization should be applied later. In addition, soybean cake slurry should be fed in sunny and warm weather to promote gonad development.

The main feed for black carp broodstock is snails and clams, supplemented with bean stool cakes and other fine feeds.

Grass broodstock are fed mainly with green feed such as green grass, ryegrass, and sweet potato vines, supplemented by macro-closed fine feed. If there is insufficient green grass in spring and autumn, fine feed should be the main feed.

To keep the water fresh, water should be added frequently in autumn and the water depth should be kept above 1.5 meters in winter.

5. Pay attention to determining the appropriate date for early induction of labor: After the weather turns warmer, it is more suitable when the lowest water temperature in the morning remains above 18°C ​​for three consecutive days and there is no strong cold air invasion.

Appearance characteristics of mature broodstock:

The female fish has a swollen abdomen, and the two sides near the genital opening are plump, soft and elastic. The genital opening is relaxed. At the same time, the scales on the abdomen of grass carp are loosely arranged, the midline of the abdomen is concave, and the ovaries are drooping, as if moving, which has a good effect of inducing labor.

Male fish that can squeeze out milky white semen that disperses when it comes into contact with water can be used. Generally, female fish are injected with 1,000 international units of chorionic gonadotropin or 40-50 micrograms of LRH-A per kilogram of body weight; male fish are injected with half the amount.

6. Optimize the hatching process. The hatching water should be filtered with a filter to prevent floating objects and wild fish from entering. Clean the hatching tank and hatching tank before each hatching, provide appropriate water flow during the hatching period, and frequently turn the water to check whether there are accumulated eggs and fry in the bottom corners, and clean them in time to maintain water quality.

7. Comprehensive prevention and control of fish diseases In the breeding of broodstock, prevention of fish diseases is the main approach. In spring and autumn every year, 0.4ppm crystal trichlorfon is sprayed throughout the pond to prevent parasites. From April to October, 30ppm quicklime or 1ppm bleaching powder is sprayed throughout the pond once a month to prevent bacterial diseases. Once a fish disease is found, the right medicine should be taken to cure it as soon as possible. In the mid-1960s, there were 36 spawning grounds for domestic fish distributed in the section of the river from Chongqing to Pengze, Jiangxi. After 1969, the spawning grounds such as Xinmatou, Xinxiakou and Xiachewan in the middle reaches of the Yangtze River no longer exist due to the straightening of the river. After the construction of the Gezhouba Water Conservancy Project, there was no significant change in the environmental conditions and the regularity of the river floods for domestic fish breeding in the mainstream of the Yangtze River. There was no major change in the spawning grounds of the four major domestic fishes. Only in the section of Sanduping to Shilihongjiang in the front section of the reservoir, there were few spawning activities of domestic fish due to changes in hydrological conditions. According to a survey in 1986, there are 30 spawning grounds of a certain scale from Chongqing to Sijia Town, of which 11 spawning grounds are distributed in the section from Chongqing to Sanduping, accounting for about 29.6% of the spawning volume of the whole river; there are 11 spawning grounds in the section from Yichang to Chenglingji, accounting for about 42.7% of the spawning volume; there are 8 spawning grounds in the section from Chenglingji to Wuxue, accounting for about 27.7% of the spawning volume. In addition, there are also smaller spawning grounds in Fuchikou, Jiujiang, Hukou and Pengze.

The quality of the four major carps varies in different sections of the river. Grass carp is the main domestic fish fry in the upper reaches of the river, accounting for more than 80% to 90% of the total number of domestic fish fry. Grass carp and black carp are the main domestic fish in the Yichang to Chenglingji section of the river. In Zhicheng and Jianli, grass carp account for 62.8% and 61.4% of the total number of domestic fish fry, respectively; black carp account for 37.1% and 29.8%, respectively.

According to analysis and speculation, after the completion of the Three Gorges Project, the eight spawning grounds located in the reservoir below Fuling will disappear due to significant changes in hydrological conditions. Domestic fish that grow up and reach sexual maturity in the reservoir will migrate upstream to the river sections above the backwater areas of the main and tributary rivers to reproduce and form new spawning grounds. As the number of parent fish increases, the scale of spawning will increase accordingly. After May, the average flow rate in the Three Gorges Reservoir is greater than 0.5m/s. The fish eggs that have not yet hatched in the reservoir can still drift with the water and continue to hatch into young fish with certain swimming abilities, and a large number of fry will remain in the reservoir.

Water temperature is one of the factors that restrict the spawning of domestic fish. During the breeding season of domestic fish, the water temperature of the Yangtze River mainstream fluctuates between 18 and 28°C, and the peak spawning period is 21 to 24°C, and the lower limit of spawning water temperature is 18°C. The Three Gorges Reservoir is a gorge-zaojingu type reservoir. After the construction of the reservoir, there will be no large-scale stable water temperature stratification phenomenon, but during the warming period, some tributaries and local main stream reservoir sections may experience short-term water temperature stratification. There is short-term water temperature stratification in the section near the dam from April to May, but the outflow water temperature in late April has exceeded 19°C, which can meet the water temperature requirement (18°C) for fish spawning. In addition, since the plankton in the reservoir will be richer than in the original Yangtze River channel, the environment is conducive to the fattening and growth of silver carp and bighead carp, and their resources will increase compared to before the construction of the reservoir.

The 11 spawning grounds of domestic fish distributed in the Fanjiang section from Yichang to Chengling are the most important breeding areas of domestic fish in the Yangtze River. The important factor for the breeding of domestic fish in this section of the river is the flooding conditions. Under natural conditions, a flooding process takes several days or more, the flow rate continues to increase, and a steep flood peak is formed, and then the flow rate gradually decreases. After the construction of the Three Gorges Project, the reservoir operates at the flood control limit water level from June to September.

The floods that occurred upstream in May and June were mainly discharged through the generator sets, so that the reservoir gradually returned to the flood control limit water level. The runoff discharged through the units is different from the natural flooding process. The flood peak in the flooding process is low and the increase is small, which affects the spawning activities of domestic fish. Therefore, after the construction of the Three Gorges Project, the reservoir should be comprehensively dispatched and operated from late May to mid-June, and several large discharge flows should be arranged to strengthen the flooding process in the river section downstream of the dam and create the required hydrological conditions for domestic fish spawning in the middle reaches of the Yangtze River. Ensuring good water quality is the key to breeding broodstock. Flushing more and more frequently can regulate the water quality of the pond, improve the pond water environment, and promote the early maturity of the gonads of broodstock. Starting from the water temperature of 10℃, flush the water once a day, increasing the water level by 3 to 5 cm each time. The silver carp and bighead carp broodstock ponds should be flushed once a week. In the half month before delivery, grass carp should be flushed once a day for 2 hours each time. The silver carp and bighead carp ponds should be flushed once every 2 to 3 days. After reaching the highest water level, new water should be pumped out.