Detailed Explanation of Key Techniques for High-Yield Artificial Farming of Rainbow Trout
Rainbow trout originated in the streams at the foot of Mount Shasta in California on the west coast of the United States, and were later introduced to dozens of countries for artificial farming. Rainbow trout is a cold-water fish, living in water temperatures of 2-25°C, with the optimal growth water temperature being 12-18°C. Rainbow trout has tender flesh, a delicious taste, many bones but few spines, and is rich in nutrients; it has always been regarded internationally as a premium fish. Rainbow trout farming in China began in 1959, with a small number of eyed eggs and fry introduced from Korea, first trial-farmed in Heilongjiang, and later expanded to Beijing, Shanxi, Liaoning and other provinces. Today, rainbow trout farming is found in more than 20 provinces, municipalities and autonomous regions across the country.
Water Quality Requirements for Rainbow Trout Farming
1. Temperature. This is an important condition; the water temperature should ideally be 12-18°C in all four seasons, and the maximum summer water temperature must not exceed 24°C.
2. Dissolved oxygen. Dissolved oxygen in the water should be above 7 mg/L, and at minimum generally not below 5 mg/L.
3. Water flow rate. A relatively large flow rate is required; the larger the flow, the larger the farming scale and the higher the yield. Generally, a flow of 1 liter of water per second has a production capacity of 100-200 kg.
4. The water quality is required to be clean, free of pollution, and free of silt.
Conditions of the Farming Pond
1. Pond shape. The shapes of rainbow trout ponds vary from place to place, but rectangular is the most common. The length-to-width ratio is generally 8:1-10:1, and an appropriate ratio can be determined according to the terrain. A certain slope (1/50-1/100) should be maintained from the inlet to the outlet to facilitate water exchange and waste discharge. Ponds can be arranged in a stepped, cascading layout making use of the terrain.
2. Pond area and depth: the following dimensions can be roughly used as a reference:
| Pond type | Area (sq m) | Depth (m) |
| Hatching pond, fry pond | 2-6 | 0.3-0.5 |
| Fingerling pond | 16-30 | 0.3-0.6 |
| Juvenile fish pond | 50-300 | 0.6-0.8 |
| Adult fish pond | 100-700 | 0.8-1.0 |
| Broodstock pond | 200-1000 | 0.8-1.2 |
3. Pond construction. The pond structure is brick-concrete, with the inner walls smoothed with cement. The inlet and outlet are set at the upper middle part of the pond to facilitate maintaining the water level. At the same time, screens must be installed at both the inlet and outlet to prevent fish from escaping.
Fry and Fingerlings and Stocking
1. Stocking density of fry and fingerlings: reference densities for each farming stage.
| Stage | Body weight (g) | Water temperature (°C) | Density (fish/sq m) | Remarks |
| Before yolk absorption | / | 13 | 5000 | Dissolved oxygen 6-8 mg |
| First feeding 1-2 months | 0.5 | 13 | 1000-500 | / |
| First feeding 2-4 months | 3 | 15 | 500-300 | / |
| First feeding 4-6 months | 15 | 17 | 300-200 | / |
| First feeding 6-9 months | 80 | 19 | 200-100 | / |
| First feeding 9-12 months | 180 | 15 | 100-50 | / |
| Two-year-old fish | 1000 | 15 | 30-15 | / |
| Broodstock | 1000-2500 | 15 | 3-5 | / |
2. Requirements for fry and fingerlings. Strong physique, uniform size, no injuries, no disease.
3. Fry and fingerlings must be disinfected before stocking.
Feed Requirements
1. The protein requirement of rainbow trout is 40%-45%; the feed is required to be nutritionally complete, with a crude protein content of around 45% for juvenile fish and no less than 40% for adult fish. The feed must have a relatively high fat content, and attention should also be paid to adding minerals and vitamins.
2. Feed materials can be sourced locally, using animal-based raw materials such as small fish, small shrimp, animal offal, pig blood, silkworm pupae and earthworms, mixed and processed at different stages in different proportions with soybean cake, wheat flour, corn, bran, vegetables, etc. into pelleted feed for feeding. For example, at the fry and fingerling stage, animal feed can account for about 60%, about 50% for adult fish, and about 40% for broodstock.
3. The feed must be fresh. The use of moldy feed is strictly prohibited.
Daily Management
1. Feeding. Adult fish are fed twice daily, at 9 a.m. and 3 p.m.; fry and fingerlings can be fed 1-2 additional times per day. The daily feeding amount is calculated based on fish body weight, accounting for about 3%-4% for juvenile fish and 1%-2% for adult fish.
2. Fish grading. After a period of rearing, rainbow trout will show differences in individual size, so regular grading is necessary to keep the fish in each pond basically uniform in size.
3. Strengthen fish disease prevention and control work; when diseased fish are found, treatment measures must be taken immediately, and dead fish must be removed promptly.
4. When oxygen deficiency occurs, oxygenation measures should be taken to prevent fish from suffocating to death.