The bodies of fish.

Fish come under vertebrates and hence have features common to them. These include a skeleton, outer covering of skin over the skeleton, a heart, a brain. But they differ from other vertebrates and from each other in a number of ways.The locomotive organs of a fish is fins, while for other animals it is a leg. Most fish breath through gills, but animals through lungs. In fact the fish differ from each other too. But in a number of ways, a fish's body differs from that of other vertebrates. For example, fish have fins instead of legs, and gills instead of lungs ( at least most do - an exception ). External anatomy

Most fish ( Note : there are exceptions, like rays that are not bullet like ) have a bullet shaped ( or rather streamlined ) body. The head is a bit bulging. Fish do not possess a neck. Due to this, the head is attached to the trunk with no distinction at the joint and slowly merges into a tail. Note that at this ends most common features among most fish. Tuna are bullet shaped, rays flat, and some like a rock ( stonefish) and some more are like snakes ( eels ).

Skin, and colour

Most fish have around the same kind of tough skin. It contains all the necessary parts a skin should have like blood capillaries, nerves, connecting tissue. But fishes have other special parts, not found under skins of some other animals. Like the mucus secreting organs that produce a slimy secretion called mucus. This secretion is helpful to the fish. This helps them in slipping away from the eager paws of hungry animals. Other cells - namely chromatophores - are very useful as they help the fish in hiding themselves by changing their colours. This is a feature that is also found in chameleons. There are some basic colours that combine to form other colours. Thus they are effectively camouflaged hidden from the watchful eyes of predators.

Fishes have adapted to their surroundings even in the sense of colouring . The fishes that lie near the ocean bed are brown in colour to match the colour of the mud found at the bottom. In fact, when the sun strikes the fish, sometimes, bright colours are produced. Bright colours that are found in fish, often warn the enemies about it's poisonous nature. Thus the fish protects itself, and also the predator.

Scales:

Most jawed fish have scales. Scales for a fish can be considered armour for a fish. The kind of scales a fish has varies from fish to fish, just as almost everything does. Teleost fish have bony scales that are not to thick and are rounded. There are divisions in the kinds of scales between a species of fish too. The two main kinds of scales possessed by a teleost are ctenoid and cycloid. Ctenoid possess scales are composed of tiny points on their surface. This kind of scale can be found in fishes that are not smooth to touch - like bass. Cycloid scales on the other hand are those smooth ones.. Cap and Salmon possess this . Sharks, most rays possess a different kind of scale, namely those which resemble closely spaced teeth. covered with placoid scales, which resemble tiny, closely spaced teeth ( shows a sharks nature ). Some fish, are scale less, but have other means of defense, like eels..

Fins are those parts of a fish that poke out of the main body, helping it in balance, swimming . Most of the modern bony fish, have fins of the ray kind ( at least the bony fish that have fins do ). In this, the fins is a stretch of skin that is placed across a group of bones that come out like rays. A fish moves the fins with muscles. movable structures that help a fish swim and keep its balance. A fish moves its fins by the helps of muscles. Except for a few fin less species, all modern bony fish have rayed fins. Some primitive bony fish also have rayed fins. These fins consist of a web of skin supported by a skeleton of rods or called rays. Some of the fish have soft rays, some hard, some spiny that are hard and sharp. Sharks and rays and chimeras have their fins hard and fleshy. The flesh and skin is supported by tough rays, made of a hard substance keratin.

Fins can be classified by structure, or even position on the body. Fish that are classified on the latter bases, are either single ( median ) or paired. The median fins are those that do not have a similar fin on the other side of the fish.

The single fins are those that are found on the back, underneath the fish and on the tail of the fish. These fins are dorsal, caudal, . The dorsal fin helps the fish stay upright in water - it helps in the balance of the fish. It grows on the top of the fish ( It's the fin that comes out of the water in a shark ). The caudal fins is at the end of the tail are acts both as a rudder and propeller. It helps in moving the fish forward as well as in changing it's direction. The fin is found below the fish, near the tail. It helps in maintaining the balance of the fish.

The paired fins include the pectoral and pelvic fins. The former is found on just behind the head of the fish. The Pelvic fins are found behind the Pelvic fins. But sometimes they are just behind the head and sometimes as far away as to be close to the fins. These fins main use is to help the fish in turning, just as the bird wings, to help it stop.

Skeleton and muscles

A skeleton is important for any animal, be it a fish bird or a human. The skeleton of a fish provides a frame for the heard, body, tail. The main frame consists of a backbone. This backbone consists of many parts namely vertebrae that are made of bone or cartilage. Attached to the backbone are ribs. The skull acts as a brain case, protecting the brain.

Fishes have three kinds of muscles: Voluntary, involuntary and heart muscles. Voluntary muscles have stripes. They help in controlling voluntary actions like movement of the fins. They have stripes. They are attached to the skeleton. Involuntary muscles have no stripes. They are not controlled by the fish directly. They do work by the will of the fish. They are found in the internal organs of the fish. The heart muscles of the fish are found only in the heart of the fish. They too have stripes unlike voluntary muscles. But they are highly branched.

Systems of the body

Respiratory system. Most fish breath under water, unlike most animals. They use the dissolved oxygen in the water to breath. They gulp water through the mouth and it passes over the gills. The gills are generally in a gill chamber. Each gill has filaments ( two rows per gill ) that are called gill filament. These filaments do the real work. They absorb oxygen from the water and replace it with carbon dioxide. There is a covering called operculum found over the gills in bony fish. In sharks, this is absent. The gills are visible on the outside too.

Special organs

Bony fish have an air bladder situated below the backbone. This organ helps the fish in rising up and going down. This provides buoyancy to the fish . This serves as a lung in air breathing fish. The bag is filled by most fish by gases from their blood. Water pressure increases with depth. As a fish goes down, the pressure causes the bladder to shrink and reduces buoyancy. Some fish, like sharks and rays, lack such a bladder. Hence to stay afloat, the must swim continuously. When they rest, they sink.

The fishes that produce light or electricity are not few. These are variations of organs found universally in fishes. Many produce light from parts found in their skin. Some produce electricity from organs developed from muscles in moving parts like eyes, body, gills.