Sharing Experience on Water Quality Control in Rainbow Trout Farming

Water quality conditions are an extremely important aspect; the quality of the water directly determines the success or failure of rainbow trout farming production.

Rainbow trout is a fish that favors counter-current flow and high oxygen; the stimulus of water flow not only accelerates material metabolism within the body but also carries away waste. The suitable flow velocity for rainbow trout is 2-3 cm/second, and the dissolved oxygen content in the water is generally required to be above 5 mg/L. In industrialized farming, the dissolved oxygen in the water must reach above 9 mg/L; at this level, appetite is strong and growth speed is fast.

In summer rainbow trout farming, dissolved oxygen must be kept from falling below 5 mg/L, because when dissolved oxygen in the water falls below 5 mg/L, rainbow trout show discomfort and their breathing rate increases. When dissolved oxygen is 3 mg/L, it can cause massive suffocation and death of rainbow trout.

Rainbow trout favors clean and transparent water; suspended matter in the water falling on the gills can cause breathing difficulty and, in severe cases, suffocation. Young fish are especially sensitive to turbid water.

For rainbow trout, the optimal pH range is pH 6.5-6.9. The ability to adapt to salinity increases with individual growth.

Rainbow trout farming generally adopts the flowing-water high-density rearing method, so the size of the water flow determines the scale of the farming water surface. Under normal circumstances, to build 600 sq m of farming water surface, a water injection rate of 100 liters per second is needed to ensure the water exchange volume.

Because flow rate is directly proportional to dissolved oxygen in the water, the flow rate must be adjusted during management of the floating fry rearing period. The flow rate cannot be too large; when too large, the fry consume too much energy swimming against the water and may even press against the outlet net and die; when too small, it cannot ensure the dissolved oxygen needed for fry growth and development, so adjustment should be made according to the dissolved oxygen in the pond water, the activity and feeding of the fry, and other conditions. Under normal circumstances, through observation, the flow rate can be controlled so that the fry do not press against the gate net.

Newly floating fry have a relatively poor ability to resist disease invasion, so according to the amount of residual bait and excrement in the water, the waste at the bottom of the pond must be cleaned away at any time. The drainage outlet mesh is small, so the net must be checked and brushed at any time every day to remove waste accumulated on the net and ensure smooth water flow.

During adult fish farming, when the maximum water temperature exceeds 22°C, it poses a threat to rainbow trout farming, so the rise in water temperature must be controlled.

Rainbow trout favors clean and transparent water; the pond water color should be clean and transparent, with color degree generally below 30 degrees, and suspended matter in the water should be less than 15 mg/L. Chemical substances in the water should conform to the range of the ministerial standards for fishery water use.

When the water source and water environment already meet the conditions, consideration should be given to making full use of the terrain to create a certain amount of water drop and flow velocity, so as to achieve gravity drainage and irrigation, reduce pumping power, and lower production costs.