EVERYDAY SCIENCE

Detailed explanation-1: -Scales. Most species of bony fishes are covered with and protected by a layer of plates called scales. There are four different kinds of bony fish scales: cosmoid, ganoid, cycloid, and ctenoid. True cosmoid scales are found only on extinct Crossopterygians.

Detailed explanation-2: -Many fish have an outer covering of scales. Scales protect fish, much like a suit of armor. All fish have a slimy covering of mucus. This substance allows the fish to swim through the water with very little drag and also makes it difficult for other organism to attach to the fish.

Detailed explanation-3: -There are four types of fish scales-placoid, cycloid, ctenoid (pronounced ‘ten-oid’), and ganoid. Most bony fish have cycloid scales. Fish with cycloid scales have the same number of scales their entire lives-the scales enlarge to accommodate a fish’s growth (scales that are lost to injury will be regrown).

Detailed explanation-4: -Fish scales are composed of a surface layer containing hydroxyapatite, calcium carbonate and a deeper layer made up of mostly collagen type I.

Detailed explanation-5: -The skin of all fish species, like that of any other vertebrate, consists of two basic layers: an outer, the epidermis, and an inner, the dermis (1, 2). The entire outer surface of a fish, including the body and fins, is completely covered by epithelium.