Biology of Aquatic Organisms - Fish anatomy

Fish are aquatic vertebrates with fins for appendages. They "breathe" by means of gills. Fish make up the largest of the vertebrate groups with over 20,000 species. They can be found in a great variety of lakes, streams, oceans and estuaries. Fish are divided into two groups based on the composition of their skeletons. The sharks, skates and rays are cartilaginous fish. Their skeletons are made of cartilage, the same flexible material in your ear lobes and nose. The majority of fish have skeletons made of bone and are called bony fish....