Fish by Family
It can be tempting to think that one fish is very much the same as another. Indeed, in some ways, nothing could be closer to the truth. All fish require water to survive, breathe using gills and have appendages called fins. However, that’s where the reality of it ends. Scientists specializing in the study of fish, professionally known as ichthyologists, class the living fish of today into four different categories. Each class boasts essential differences that separate it from the others.
The class Chondrichthyes, for example, contains the sharks, stingrays, and other cartilaginous fish. Instead of bones, these fish sport cartilage. Additionally, these fish have no gill flap to protect their series of five gills. This order is predominantly marine. Some freshwater aquarium fish do belong to this order – the freshwater stingrays for example. However, the large size and extremely high maintenance requirements of these fish make them inappropriate for more hobbyists. Additionally, these fish are very expensive, often fetching several hundred dollars for a single specimen.
On the other hand, the class Actinopterygii contains most of the fish that we know and love. These fish have bones, an operculum or gill flap covering their gills, and occur in both fresh and saltwater.