About 40- 120 kg of salt. 1-3 kg of salt in 1 cubic fish pond, the concentration can be controlled below three thousandths, and the highest salt content in 40 cubic fish pond is not more than five thousandths. By adding salt to improve the osmotic pressure of water, although it will not be higher than that of fish, it can also reduce the infiltration of water, thus avoiding the invasion of bacteria. Fish farming is a technical activity, which not only requires fish farmers to have certain professional skills, but also requires certain feeding experience. Adding salt is a common operation in fish farming, which can change the osmotic pressure of fish. The osmotic pressure of fish is higher than that of fresh water, and water will continue to penetrate into the body. If there are some bacteria in the water, they will also enter with the water, thus playing a role in disinfection and sterilization of fish and ensuring the healthy growth of fish.