鱼类是最古老的脊椎动物。它们几乎栖居于地球上所有的水生环境中,包括淡水的湖泊、河流还有咸水的大海和大洋,可以说只要有适宜的水生环境,就会有鱼的存在。当我们说到鱼,不同的人可能会有不同的联想。有的人可能会想到身体呈流线型的鲤鱼,有的人可能会想到身体扁平侧偏的蝴蝶鱼,以及生活在洞穴中躯体长成棍棒状的鳗鱼,还有珊瑚礁 Fish is the oldest vertebrate. They inhabit almost all the aquatic environments on earth, including freshwater lakes, rivers and saltwater sea and ocean. It can be said that as long as there is a suitable aquatic environment, there will be fish. When we talk about fish, different people may have different associations. Some people may think of streamlined carp body, some people may think of the body flattened butterfly fish, as well as living in caves in the body into a stick-shaped eel, and coral reefs