CHAPTER II 



CHARACTERISTICS AND HABITS OF FISHES 



FISHES are the most primitive vertebrate, i.e. back- 

 boned, creatures known. All reptiles, birds, and animals 

 have gradually evolved from fish-like ancestors by a 

 series of age-long processes, the stages of which are 

 recorded in fossilized remains that are found in various 

 rock strata throughout the world . A fish lives exclusively 

 in water. It has no lungs, but extracts oxygen from the 

 water as it passes over the surface of its gills. Instead 

 of limbs, it has fins, with which it balances itself and 

 propels itself through the water. Its skin is either 

 bare, e.g. the cat fish, or is covered with scales, e.g. the 

 herring, or with bony plates, e.g. the sturgeon. The 

 skin of certain sharks is studded with minute teeth and 

 produces, when cured, the well-known shagreen leather. 

 In nearly all cases the skin of fishes is liberally supplied 

 with small glands which constantly produce a lubricating 

 mucus. This mucus greatly reduces friction between the 

 fish and the water through which it moves. 



The body of a fish is adapted to move swiftly and 

 smoothly through the water ; it is shaped more or less 

 like a torpedo, but this form is greatly modified in 

 different species. Certain species of fish living at the 

 bottom of the sea, for example skates and rays, have 

 become flattened, as though by a pressure applied 

 vertically downwards. Others, for example plaice, 

 flounder, sole, appear to have been flattened sideways. 

 In the various members of the eel family, the body is 

 greatly elongated. 



The body of a fish is generally coloured and marked 



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