Species: About 24,500
Fish form the largest group of vertebrates. There are Four Classes of fish that we lump together though they are only distantly related to each other. The four groups of fishes are: Jawless Fishes (2 classes), Cartilaginous Fishes, and Bony Fishes. Jawless fish have round mouths. Many are parasite fish and will attach to a host fish to feed. In central Illinois we have sucker fish that fit in this category. Cartilaginous fish have no bones. They are held together with cartilage, like the bendy stuff in the tip of our noses. Sharks are the well know cartilaginous fish. Bony fish are the most common. Blue Gill, Carp, Bass, Crappie, Walleye, are central Illinois’ examples of these fish. Fish have scales and are cold-blooded. Fish can live in salt water or fresh water environments, although a few species can move between the two. Fish are built for water. They usually have a streamlined body with smooth scales. They have fins to provide power, steering and stability. All fishes have gills for extracting oxygen from the water.