The great diversity of fish and their main characteristics

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• In addition to the absence of jaws, modern agnathans are characterised by absence of paired fins. e.g. lampreys 
• They are jawed vertebrates with paired fins, scales, and skeletons made of cartilage rather than bone. e.g. sharks and rays
• have skeletons primarily composed of bone tissue, as opposed to cartilage. Is the largest class of vertebrates in existence today with ~ 28,000 species e.g. guppies, clown fish
• Are a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water and excretes carbon dioxide.
• Fish have an internal skeleton either made of bone or cartilage. That is one important characteristic that differentiate fish groups; Bony fish and Cartilaginous fish.
• Blood passes only once through the heart in each complete circuit of the body except for lungfish.
• They are fish, but they have a horse-like head, a monkey-like tail and a kangaroo-like pouch. They have a few things in common with chameleons as well – they can move their eyes around, and change their skin colour!
• Entices prey close with the glowing lure that comes from luminous bacteria that live in it.
• Their leafy camouflage and spiny fins keep large fish from snacking on them. They slurp up their food, using their long snout like a drinking straw.