How to raise adult rainbow trout? Detailed explanation of rearing methods

The main rearing methods for adult rainbow trout are as follows:

1. High-density flowing water pond trout culture. This is currently a rearing method commonly used both domestically and abroad. It has the advantages of small land area, saving manpower and material resources, high feed utilization rate, and high yield. 2. Using deep-layer low-temperature water from high-dam reservoirs to raise trout. In high-dam reservoirs, water temperature is directly proportional to water depth: surface water temperature is high, while bottom water temperature is low. Using the deep-layer low-temperature water discharged from tunnels for power generation or irrigation at high-dam reservoirs, cage culture of trout can be carried out in downstream channels near the reservoir area. Here, the Xin'an River rainbow trout farm in Zhejiang is taken as an example for introduction. (1) Rearing situation. Twenty kilometers downstream of the Xin'an River Reservoir dam, the flow is abundant, with many aquatic plants, small fish and shrimp. In recent years, the warm-water fish species growing there have been decreasing day by day, while raising rainbow trout there has uniquely favorable conditions. In January 1980, the Fisheries Administration Bureau of Jiande County, Zhejiang introduced 30,000 eyed rainbow trout eggs from Taiyuan to local incubation, hatching a total of 10,500 fry. On April 5 of that year, they were moved outdoors and transported to the river surface 3 kilometers downstream of the Xin'an River dam, where cage culture was carried out. The water temperature at the rearing site was 9°C-20°C, and the monthly average temperature varied from 10.3°C—16.2°C. When the water flow was rapid, the flow velocity was 0.2 m per second. During the cage rearing process, 6,000 fish accidentally escaped into the river. As of December, 4,500 fish remained in the cages, with an average body weight of 75.7 grams. As of November 1981, more than 4,000 adult fish had been raised, with an average body weight of 880 grams. As of December 1983, the average body weight was 2,400 grams. (2) Cage specifications and stocking density. ① Broodstock cages. Specifications are 4 m×4 m×1.7 m, area 16 sq m, underwater volume 24 cubic meters, mesh 4.5 cm, woven from 3×4 polyethylene filament. Stocking density is 10 fish per sq m, 6 fish per cubic meter. Netting with 9 cm mesh is used as the cover net. The mesh of broodstock cages is relatively large, mainly considering that it allows small miscellaneous fish to enter the cage and serve as rainbow trout feed. ② Adult fish cages. Specifications 4 m×4 m×1.7 m, area 16 sq m, underwater volume 24 cubic meters, mesh 3 cm, with 6 cm mesh netting used as the cover net. The nets are all woven from 3×4 polyethylene filament. According to 1981 experiments, stocking densities of 100 fish and 63 fish per sq m showed little difference in adult fish growth rate, survival rate, etc. In 1983, 125 fish were stocked per sq m, and the fingerlings entering the cages were over 50 grams in size. ③ Fingerling cages. Fingerling cages are divided into two levels. The first-level fingerling cage has specifications of 2 m×2 m×0.7 m, area 4 sq m, underwater volume 1.6 cubic meters, made from 16-mesh polyethylene netting per sq m into a closed six-sided shape, with one edge left unsewn as a feeding opening. The first-level cage is stocked with fingerlings below 11.5 cm, at a stocking density of 2,500 fish per sq m. When the fingerlings grow to over 11.5 cm, they are moved to the second-level fingerling cage. The second-level cage has the same specifications as the first-level cage, made from 1.5 cm mesh netting, with a stocking density of 400 fish per sq m. This design of the fingerling cage mainly takes into account that small mesh is easily clogged by blue-green algae. This style makes it convenient to turn the cage in water, using the cage bottom as a cover. After being exposed to the sun, the blue-green algae falls off, and it can also prevent bird damage. If the cage sinks into the water, it can also prevent fish escape. The cages all use moso bamboo frames and are of the floating type. (3) Feed. The trout feed at the Xin'an River rainbow trout farm uses locally cheap pig blood, mainly pig blood and wheat bran, supplemented with fish meal, aquatic plants, etc. The feed system for the fingerling stage is 2.74, and the feed system for the adult fish stage is 3.05. Adult fish and broodstock are fed twice daily, and the feed cost per net increase of 0.5 kg of fish is 0.66 yuan. 3. Transplanting and stocking rainbow trout in mountain streams and brooks. Rainbow trout originated in mountain streams, with insects and small miscellaneous fish as their main food. Mountain streams and brooks mostly contain small fish of low economic value. If rainbow trout are transplanted and stocked into such waters, because rainbow trout are limited by their own living water temperature threshold, they will not spread arbitrarily, thereby achieving the effect of converting low-grade miscellaneous fish into high-grade fish. In 1983, the Sichuan Provincial Department of Water Resources began transplanting and stocking experiments of rainbow trout in the Dahaizi of the Min River and the Jiulongzhai Nature Reserve. 4. Seawater cage culture of rainbow trout. In recent years, seawater cage trout culture has developed rapidly. In 1982, Norway's seawater trout culture was about 400 tons, France about 700 tons, and Denmark, Japan, etc. also widely practiced trout culture. The cage specifications used include 10 m×10 m×10 m, 7 m×7 m×3.5 m, etc. Stocking density is 4—5 kg per cubic meter, and production is 15—20 kg per cubic meter. The rearing period is mostly from October to June of the following year, ending when the seawater temperature reaches above 18°C. Denmark's seawater cage culture generally stocks 200-gram rainbow trout in April, and by January of the following year they grow to 2—3 kg. North Korea has also succeeded in acclimating and raising trout in seawater, which only requires enclosing an area at the seaside with wire mesh or ordinary fishing nets. In 1983, Linqu County in Shandong, Changdao, and the Dalian Fisheries Company of China also carried out seawater field cage trout culture experiments. According to experiments, the growth rate of rainbow trout in seawater is 1.5 times faster than in freshwater.