Transplantation and propagation techniques of whitebait in large water surface

The silverfish belongs to the salmon order, the silverfish family. It is an annual small fish, which is only distributed in the coastal and inland waters of Southeast Asian countries and regions such as China, Japan, Korea, Vietnam and the eastern part of the former Soviet Union. There are more than 10 species of silverfish in China. It is widely distributed in coastal and Tongjiang rivers and affiliated lakes and reservoirs, feeding on zooplankton, small fish and shrimp. Now the main points of the techniques for transplanting and multiplication are summarized as follows: first, the transplanting species 1, large silverfish; the body length is generally 110-160mm, which lays eggs in winter; the number of eggs is 6000 meters, the mature eggs are crystal clear and full, and the egg membrane filaments are distributed densely, with different techniques. The juvenile fish mainly feed on zooplankton, and the adult stage is transformed into small fish and shrimp food. 2. Taihu Lake new silverfish (small silverfish): the body length is generally 60-70mm, which can be divided into two spawning groups in spring and autumn in the middle and lower reaches of the Yangtze River. the peak spawning period of Spring Festival is the first and middle of April and autumn is the first and middle of October; the fecundity is generally 1000ml 5000, and the membrane filaments of mature eggs are fractionated or radiated short-term; they feed on zooplankton for life. The transplanting of these two kinds of silverfish is affected by geographical and climatic conditions, the new silverfish in Taihu Lake is more suitable to be transplanted in the south of Huaihe River, and the large silverfish is more suitable to be transplanted in the north of Huaihe River. Second, the environmental conditions of the transplanted water area 1. Water area: reservoirs and lakes directly above 2000 mu. 2. Water level and water depth: it is better to keep the water level relatively stable, and measures to avoid the loss of silverfish resources should be considered in irrigation reservoirs or over-water lakes with large drop. Shallow water reservoirs are beneficial to the reproduction of silverfish. The water depth of about 15 meters is better, but the water depth is not the main limiting factor for transplantation (the average water depth of 87 meters in Fuxian Lake, Yunnan has been successfully transplanted with silverfish). 3. Water temperature: the suitable temperature for spawning of new silverfish in Taihu Lake is 15Mel 20 ℃, and the optimum temperature for spawning of large silverfish is 2Mel 6 ℃. 4. Water quality and sediment: the salinity can be about 1000mg/L; the transparency range is 25: 100 cm; the PH is not more than 9; the sediment is better with hard sand bottom. 5. Food organisms: the biomass of zooplankton feed is generally not directly lower than that of 1.0mg/L, and the population composition of Cladocera and copepod is better. In addition to a certain amount of zooplankton, the waters where large silverfish are transplanted should have relatively abundant bait resources for small fish and shrimp. Method of fertilized egg transfer 1. Time: from March to April, the water temperature of the new silverfish in Taihu Lake is about 15 ℃, and the water temperature of the big silverfish is 2 ℃ from late December to January. 2, transport: the transport volume is less, when the journey is short, put an appropriate amount of lake and reservoir water filtered by 120 mesh screen (or skimmed cotton) with open utensils or plastic buckets, 1 liter of water can hold 3000 million fertilized eggs; transport volume is large, plastic bags can be used for long distance transportation in insulation buckets, and 10,000 fertilized eggs can be released in 1 liter of water. It is better to keep the temperature in the transport water consistent with the temperature when the fertilized eggs hatch, so as to avoid breaking the membrane and emergence of seedlings during transportation. 3. Release: put the fertilized eggs directly into the water to make them hatch naturally on a hard or sandy bottom. The location of laying eggs should be leeward and sunny, the water body is stable, the water depth is 1.5-2.5m, the bottom is gentle, the bottom is hard and sandy (such as lake bay, reservoir bay fresh water area, shelter from the wind near the shore). When laying eggs, the eggs should be evenly distributed in the water, and several more points should be selected for release. Under the condition that the bottom quality of the laying site is not ideal, the method of placing the incubator can be adopted, that is, the incubator is made of window screen into a 4 × 4 × 4m3 incubator, the incubator is suspended at 1.5m underwater, and the drama box is lifted after 7ml for 10 days, and the embryonic development is observed. After all the seedlings are hatched, remove the cage. 4. Transplant density and effect 1. Transplant density: the general rule is that the density of transplant is large, the quantity is large, the incubation period is short, and the yield of fish is fast. (1) transfer of fertilized eggs: the number of eggs released is calculated on the basis of the hatching rate of 70-80%, with 70 eggs per mu, usually cast again in the second year. (2) transfer of larvae: continue hatching and management of the returned fertilized eggs. The average hatching time of new silverfish in Taihu Lake was 126hrs at 15.6 ℃, 81hrs at 20 ℃, the hatching time of newly hatched larvae was 25ml 2.9mm, and the hatching time of larvae was about 40 days at 10 ℃, 4.2-49mm. It is appropriate to release the larvae when the fish reaches the level of swimming and the yolk has not been fully absorbed. The new silverfish in Taihu Lake is about 2-3 days after hatching, and the big silverfish is about 3-5 days after hatching. The release site should usually be at a certain distance offshore, with a water depth of about lm. The water temperature in the water area is the same as that in the container where the larvae are stored, and the temperature difference is not more than 2 ℃. It is appropriate to put in 40 tails of 20m / m. 2. Transplantation effect: (1) Biological effect: it is the early effect after silverfish transplantation. Silverfish can survive after moving to new waters, and some individuals naturally spawn and reproduce after sexual maturity, which can be judged in the same year or the second year of transplantation. Usually after the silverfish is moved in, especially during the sexual maturity or spawning period, the parent fish or larvae should be caught with a net with a diameter of Zm in order to check the effect of transplantation. (2) production effect: it is a population with fishing value formed after natural reproduction. The new silverfish in Taihu Lake is generally 3 years, individual 2 years. The large silverfish is usually 2 years, and some is 3 years. After the biological effect is determined, the productive net should be used for regular or indefinite trial catch in the second year to monitor its reproduction and growth. The amount of fish resources is calculated according to the assessment of general fish resources. 5. Resource management after transplantation. 1. According to the situation of monitoring resources by light trapping with the bureau net, the fishing tools, fishing time and fishing intensity are preliminarily determined. 2. Constantly explore and study the situation of resources forming the population and the reasons that affect the change of resources, adjust the operating time and intensity, and determine the proportion of reserved resources and the amount that can be caught. 3. Establish a strict management system, strengthen the management order of fishery administration, and strictly prohibit the illegal production of fried and poisonous fish. 6. Silverfish fishing 1. The principle of determining the fishing time: (1) fishing when the population reaches the maximum biomass. When the gonad begins to develop and the growth rate of body length and body weight slows down, the population biomass is the largest, and the fishery utilization is more reasonable. Therefore, it is suitable for fishing when the growth of silverfish reaches the age of 7 months. (2) arrange the fishing season reasonably and make full use of the bait basis. The biomass of zooplankton, the bait of silverfish, varies with the seasons, and its peak usually occurs in summer, followed by spring and autumn, and the least in winter. Therefore, the fishing period should avoid summer and autumn in order to make full use of the bait basis. Generally speaking, fishing in late autumn and early winter is more reasonable. (3) fishing to avoid the breeding season. 2. Fishing methods: (1) trawling: suitable for lakes and reservoirs of more than 10,000 mu. (2) the light of hemispherical Zeng net is caught through. (3) the fishing time is generally from October to November of each year.