1. The color of fish is deep and light, which is the protective color of fish.

2. The body is streamlined, with big middle and small two ends.

3. The body surface is covered with scales to protect the body; There is a layer of mucus on the surface of scales, which reduces the resistance of water when swimming.

4. There is a lateral line on each side of the body, which is connected with the nerve, mainly for judging the direction and sensing the water flow.

Fish's body has pectoral fin, dorsal fin, ventral fin and caudal fin, which are the moving organs of fish in water.

6. Fish breathe through gills.

7. The swim bladder in the body regulates the specific gravity of the body. With the cooperation of fins, the swim bladder can make the fish stay in different water layers.