|Classification of Fish
Fish are classified according to the material which makes up their skeletons. For example, sharks, skates and rays belong to a group called cartilaginous fish because their skeletons are composed entirely of cartilage. Tropical fish, which are members of the fish group that are represented in the Aquademics aquarium, are called bony fish (scientific name Osteichthyes) because they have skeletons made of bone. All of the facts and information for the Aquademics program, as well as the material in the Aquademics Parent and Teacher's Guide, will focus on the bony fish group.
The skin of most bony fish is covered with bony scales that look like shingles on a roof. Bony fish scales are waterproof and help protect the fish. Glands in the skin in which the scales are embedded secrete a layer of mucus that covers the entire body. Mucus helps protect fish from infection. Handling fish removes this mucus coating and can be harmful to the fish.
Oxygen enters the bloodstream and carbon dioxide diffuses out at the gills, which are feathery structures found along the sides of the head. The gills of a healthy fish are bright red due to the high level of oxygen in the blood that is very close to the surface of the gills. (Without oxygen, the gills would be brown.) In bony fish, the gills are covered by a bony place called an operculum.
The shape of a fish's body tells a lot about its lifestyle. Fish with fusiform, or streamlined, bodies are usually fast swimming predators that may swim at high speeds much of the time or are capable of great bursts of speed. Many tropical fish are laterally compressed (flattened from side to side). Fish with this shape are not very streamlined but they do not rely on speed for catching food or escaping from predators. Their body shape is perfectly adapted for hiding in the cracks and crevices of rocks and reef. They can move into these areas to hide, to escape predators or to get at food that cannot be reached by other fish. Fish with this body shape, like angelfish, are very maneuverable and capable of short bursts of speed. They are often camouflaged with disruptive coloration.
Other fish are flattened from top to bottom. Fish with this body shape spend most of their time at the bottom. They are usually camouflaged or can change color to match the bottom.
Fins are used for swimming and sometimes for protection. Some fins are paired and others unpaired. The paired fins are the pectoral and pelvic fins. The unpaired fins are the dorsal, caudal (tail) and anal fins. The way the fins are used varies among different groups of fish. Most fish use their tails to move through the water and their other fins to steer with. Fins are most bony fish are flexible and supported by visible spines and rays. The shape, location and size of a fish's fins are closely linked with its way of life. See more about fins.
Caudal (or tail) fin:
Fish are visual predators. Many nocturnal fish have large eyes to help them feed at night. Fish such as sharks have pupils that dilate and constrict, and some sharks also have an eyelid that closes from the bottom upward. Bony fish eyes lack both of these characteristics.
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