Fish are vertebrate animals, that's, all of them have a vertebral column or 'spine'. There are two main groups of fish, bony fish (Teleosts) and cartilaginous fish (Elasmobranchs). As the common names imply, the skeletons of teleosts are created of bone whereas the elasmobranchs have cartilaginous skeletons. The elasmobranchs comprise sharks, rays and dogfish that differ from teleosts in many respects. The teleosts are way more numerous, with a greater diversity of species than the elasmobranchs.
All fish are aquatic and breath by absorbing dissolved oxygen within the water using their gills. The bodies of each teleosts and elasmobranchs are coated with scales but those of elasmobranchs are spiky and project through the skin. This makes the skin feel very rough, like coarse sandpaper. The scales of the teleosts have a flattened, discoid form and are coated by a skinny layer of skin and mucus which probably reduces friction between the body and the surrounding water and makes them very slippery.
The swimming mechanism in each groups is very similar. A series of muscular contractions pass down every side of the fish alternately bending it from side to aspect and pushing backwards and sideways against the water. The water resistance exerts an opposite sideways and forward force on the fish. The sideways forces cancel every alternative but the forward force propels the fish forward. In each groups there are variations during this method of propulsion. Skates and rays make undulatory movements in the vertical plane as do flatfish like plaice. Some teleosts, like the sea horse, propel themselves by undulatory movements of their dorsal fin.
Generally, the fins contribute to stability and steering rather than propulsion. The median fins, dorsal and ventral, cut back the sideways thrust of the swimming movements and conjointly scale back the tendency to roll from side to side. The paired fins facilitate to steer the fish upwards or downwards through the water and contribute to turning and braking. The paired fins of elasmobranches are held in rather rigid positions whereas those of teleosts, with their flexible jointing to the body, are additional versatile in their movements and can often be seen moving gently to stay the fish in a very steady position.
In the teleosts, there is a swim bladder. An elongated, air-crammed sac just below the vertebral column. This air bladder keeps the fish buoyant and prevents it from sinking when it stops swimming. The quantity of the air bladder will be adjusted to compensate for changes in pressure at totally different depths. The elasmobranchs don't have swim bladders and thus they start to sink if they stop swimming.
Although water is H2O, aquatic creatures cannot use the oxygen from this. The oxygen they breathe comes from the air that has dissolved within the water. There are four or five pairs of gills situated within the mouth cavity. In teleosts, they're covered on the outside by a bony plate called the operculum. By movements of the ground of the mouth and operculum, the fish creates, a current of water that passes over its gills. Water is taken in through the mouth and expelled through the operculum in the case of teleosts, and out through separate gill slits in elasmobranchs. The gills are, in effect, finely branched, skinny-walled blood vessels which, because of their multiple branches, expose an monumental surface to the water and therefore facilitate absorption of oxygen and loss of carbon dioxide.
Author Resource:-
Dorish Hill Grant has been writing articles online for nearly 2 years now. Not only does this author specialize in Biology, you can also check out his latest website about:
![[Valid RSS feed]](http://www.healthandwealth4you.com/images/icon_Rss.png "XML Feed For RSS"){kind=icon}
Category Rss Feed
Print This Article
Add To Favorites
