Fish have eyes with a very wide range of vision. Between the eyes the mouth, on the uppermost side of the head, are two small vents- nostrils, but the fish does not breathe through these. Instead they are used for smelling only and have nothing to do with the respiratory system. There is a faint line running on either side of the body of a fish, which is known as the lateral line. This consists of a series of highly sensitive cells, which, by means of records of pressure, indicate distance and warm of hazard. It is, fact, a built-in radar system. In addition, some fish gave balers, which are fleshy filaments hanging from their mouth, which they use as feelers.

Breathing :
Fish have a special mechanism in the shape of their gills for extracting oxygen from the water. The gills are positioned on either side of the head, a little behind the eyes. The vital parts of the gill, the gill  filament and the gill lamella,are protected by the gill cover. the water enters the gill by way of the mouth, which contain what amounts to a non-return valve preventing the water from flowing out. It leaves through the skin fold, which functions as a valve at the opening at the rear of the gill cover. Any food particles are sieved out by the gill rakes on the inside of the gill arch. The water then flows through the gill lamells, in which is a fine network of blood capillaries to absorb the oxygen in the water into the bloodstream of the fish.


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