What Is A Fish?

Certain parrallel can be drawn between the structure of the fish and a human : both have a skeleton supporting  muscles and a heart that supply blood to all parts of body.A human's five senses are also present in the fish but are modified as required.However, the similarites end here, as fundamental changes occurred when life forms adapted to living on land.The greatest difference is in the fish's means of motion and maneuverability:fish are usually propelled by movements of tail stem ( caudal peduncle ), with the fins acting as stablizers.Nostrils  are used normally for smellling and play no part in respiration.Generally a fish's skin is protected by scales that reduce friction and protect the soft tissues from predators or parasites and even sunburn.The motion and shape of the fish's mouth depends on its feeding habit and dwelling level in the water.

FISH MOUTHS

Fish with upturn ( superior) mouths are surface feeders; a downturned (inferior) mouth facilitates feeding from the streams ; a mouth situated at the tip of the snout (terminal) often indicates a midwater feeder.

FISH COVERINGS 


The majority of scale types fall into two categories:ctenoid with small teeths on the rear edge ; and cycloid with smooth edges.Scutes are bony plates found on many catfishes.

EYE STRUCTURE

As fish eyes are carried on the sides of the head, fish do not have binocular vision and judement of distances is often inaccurate.Colours, however are preceived well.Focusing is achieved by movements of a fixed-shape lens,while in humans, it is the lens shape itself that is adjusted. 

FISH TAILS 

The shape of the caudal fin effect swimming performance and its colour may aid identification between species or providing cammouflage.The lyre-shaped and deeply cleft tails shown here facilitate speed.Bright patterns assit identification on the broad and crescent tails and sex differentiation on the round tails.Fins are cultivated for decoration only, and do not enhance function.