Understanding Freshwater Fish

Fish have managed to colonise most bodies of water, from the deepest oceans to the highest mountain pool. All you have to do is think about a place where you find water and it is virtually certain that you'll find a fish that lives in it.

Anatomy of freshwater fish

Water is much denser than air, so fish's bodies are streamlined to pass through it. Most fish have torpedo shapes bodies to enable smoother swimming, but fish from fast waters have flat bodies and expanded fins to improve their stability in the rushing currents.

Basic Anatomy

A fish's body is usually covered by scale or thick skin which afford protection. Their fins keep them upright, and provide foward power and steering. In order to maintain a certain position in the water, a fish uses its gas-filled, swim bladder which extends from behind the head for about a third of the body lenght. Combined with fatty tissues it gives the fish lift. The great majority of fish breath by extracting the dissolved oxygen from water passing over their gills. In these organs the blood vessels are close to the surface allowing oxygen to be absorbed and waste gases to be exchanged.

Taste and Smell

Although fish have nostrils, the are not use for breathing but for smelling. Fish can smell food from distance, but to taste it they have to touch it. There's no single organ of taste. Instead taste receptors are scattered across the head and body surface. Barbels are also covered in taste receptors which alloe the fish to feel through the silty subtrate until it touches food.

Vision

Most fish have eyes, although they don't have eyelids. The position of the eyes is an indicator of  lifestyle. Bottom dwellers have eyes on the top of their heads while midwater fish have eyes on the sides of their heads to provide all round vision. Some predators have developed binocular vision but the eyes of some cave in habiting species have regressed so that they are now blind.

Published by : Quantum Books Ltd.