Is black fish a freshwater fish or a seawater fish? Why is there so much mucus

Freshwater fish black fish belongs to freshwater fish and cannot survive in seawater. It is suitable for living in rivers, lakes, reservoirs or ponds with water grass or silt at the bottom. It is widely distributed in China and has been found in the Yangtze River Basin and Heilongjiang Basin. This kind of fish has mucus on its body surface, which can play a protective role, prevent the invasion of bacteria, and avoid the attack of natural enemies. 1、 Is black fish a freshwater fish or a seawater fish? Black fish is a freshwater fish. It mainly lives in rivers, lakes, reservoirs, ponds and other waters. As a benthic fish, it is suitable to live in places with dense water plants or silt at the bottom. In addition, it is widely distributed in China. In addition to the western plateau, it exists in a large number in the Yangtze River Basin and Heilongjiang Basin, and a small amount in Yunnan, * * * and other areas. 2、 Why does black fish have mucus? The mucus outside black fish mainly plays a protective role. It can not only prevent the invasion of bacteria and viruses, but also prevent harmful substances in water from entering the body. And when swimming, it can reduce the resistance and make it faster. In the face of some natural enemies, such as larger carnivorous fish or waterfowl, they can also escape the enemy's attack with the help of smooth mucus. 3、 What food does black fish eat? Black fish mainly feed on the larvae of aquatic insects at the juvenile stage, and also eat some small fish and shrimp. When they grow into adults, they will feed on all kinds of small fish. Because its distribution has great regional differences, so the food is also different. For example, in Heilongjiang, it mainly preys on carp, crucian carp and arrowhead, but in the Yangtze River Basin, it is mainly spiny loach, sand loach and loach, and this kind of fish will kill each other. （HeiYuShiDanShuiYuHaiShiHaiShuiYu，WeiShenMeNaMeDuoNianYe）