What is a Fish?
What is a Fish? Body Fish F ish are aquatic vertebrate animals that have gills but lack limbs with digits like fingers or toes. Recall that vertebrates are animals with internal backbones. Most fish are streamlined in their general body form. Bod Defining a Fish Defining a fish is difficult because the term fish includes a very wide range of aquatic animals. more over, there are about as many species of fishes than there are of all other vertebrates combined (Fig. 4.4). Of the nearly 50,000 species of animals with backbones, approximately 4,500 are mammals, 9,700 are birds, 6,500 are reptiles, 4,000 are amphibians, and 25,000 are fishes. Although some these numbers change as new species are discovered, new fishes are found more often than other new vertebrates are found. ...