Fish belongs to vertebrates. It is mainly divided into bony fish and cartilaginous fish. They basically breathe with gills, and can swim in the water and feed on their upper and lower jaws. This animal has many characteristics, such as scales on the body surface, which can avoid injury. At the same time, the fins can provide balance and let it swim normally in the water. In addition, some fish have swim bladders, which float up and dive down by adjusting the gas inside. 1、 What kind of fish do fish belong to the subphylum vertebrates of chordate. This kind of animal is characterized by breathing with gills and swimming through the swing of trunk and tail. It can feed on its upper and lower jaws. It belongs to a kind of variable temperature animal. The common fish are generally cartilaginous fish or bony fish. They can also be divided into freshwater fish and saltwater fish, or tropical fish, temperate fish and cold fish according to the water area. 2、 What are the characteristics of fish 1. Fish gills: no matter what kind of fish, they all have gills, because the characteristic of this kind of animals is to breathe with gills. When water flows through gill filaments, fish can complete gas exchange, so as to obtain oxygen and release carbon dioxide. If the fish leaves the water, the gill filaments will stick together and lose the ability to breathe.
2. Fish scales: most fish have fish scales. This is a skin derivative, usually calcium. It covers its whole body or part of its area, which can protect the body and prevent some irritation. In addition, the structure of fish scales is very special, which can make the fish have less resistance when swimming.
3. Fin: when fish swim, they rely on the tail fin to provide power. At the same time, they can also change the direction and rely on the pectoral fin to slow down and brake. Other fins are mainly responsible for maintaining balance. No matter which fin is lost, the fish will swing left and right when swimming.
4. Swim bladder: not all fish have a swim bladder. It is mainly responsible for regulating gas to change its density and facilitate fish to float or dive. If a fish suffers from swim bladder loss, it will cause it to roll over and can no longer maintain its balance. （YuShuYuShenMeLei，YuYouNaXieTeZheng）