Whales and seahorses, which is a true fish Fish and mammals are two different animals, and they are very different in some key characteristics, such as breathing patterns and so on. The basic characteristics of fish include breathing with lungs and swimming with fins, which is not the case with mammals. Seahorses do not look like fish in appearance, but they are indeed a kind of fish, a small fish in the family Syngnathidae, order Gasterosteiformes. Although their fins are different from those of ordinary fish, their tail fins have been degraded, and other fins are transparent and smaller, but they can move by swinging their fins. In addition, they also use gills to breathe. These two characteristics have led biologists to classify them as fish, even though their appearance is quite different from that of ordinary fish.
Whales, on the other hand, are more fish-like in appearance, but they are not really fish because they differ from fish in some key characteristics. For example, whales use lungs to breathe, which is very different from fish using gills to breathe.
The difference between fish and mammals is relatively large, and the way of breathing is one of the more important differences. Fish use gills to breathe, while mammals use lungs to breathe. As mentioned above, seahorses breathe with gills and are a real fish. Whales, on the other hand, breathe with their lungs and need to come to the surface to breathe. Even though it looks like a fish, it is essentially a mammal. As a kind of mammal, whales have some characteristics different from fish, such as viviparous reproduction.
