Biology- Characteristics of Fish- An Introduction
All fish are aquatic and breath by absorbing dissolved oxygen in the water using their gills. The bodies of both teleosts and elasmobranchs are covered 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 shape and are covered by a thin 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 both groups is very similar. A series of muscular contractions pass down each side of the fish alternately bending it from side to side 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 each other but the forward force propels the fish forward. In both groups there are variations in this method of propulsion. Skates and rays make undulatory movements in the vertical plane as do flatfish like plaice. Some teleosts, such as the sea horse, propel themselves by undulatory movements of their dorsal fin.
In general, the fins contribute to stability and steering rather than propulsion. The median fins, dorsal and ventral, reduce the sideways thrust of the swimming movements and also reduce the tendency to roll from side to side. The paired fins help 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 while those of teleosts, with their flexible jointing to the body, are more versatile in their movements and can often be seen moving gently to keep the fish in a steady position.
In the teleosts, there is a swim bladder. An elongated, air-filled sac just below the vertebral column. This air bladder keeps the fish buoyant and prevents it from sinking when it stops swimming. The volume of the air bladder can be adjusted to compensate for changes in pressure at different depths. The elasmobranchs do not have swim bladders and so 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 which has dissolved in the water. There are four or five pairs of gills situated inside the mouth cavity. In teleosts, they are covered on the outside by a bony plate called the operculum. By movements of the floor of the mouth and operculum, the fish creates, a current of water which 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, thin-walled blood vessels which, because of their multiple branches, expose an enormous surface to the water and so facilitate absorption of oxygen and loss of carbon dioxide.
Related Tags: fish, eggs, scales, feeding, breathing, biology, swimming, lateral line, teleosts, elasmobranchs, fins
D G Mackean is the author of GCSE Biology, IGCSE Biology, and many other Biology text books. He has a site of Biology Teaching Resources at http://www.biology-resources.com which includes a bank of Biology Experiments for teachers, sample PowerPoint presentations, and many biological drawings
Your Article Search Directory : Find in ArticlesRecent articles in this category:
- Radio Controllers - Knowing The Basics
Radio controlled models are different in design and structure, but at their core are the same radio - The Fourth Decade Of Modern Stereology 1991-2001
Modern stereology introduced an entirely new set of rules for quantification of biological objects i - Science & Technology Articles - How to buy Wireless IP security cameras
Due to the increasing need for surveillance devices, camera's production become more increasingly. I - Science & Technology Articles - Sony Ericsson Hottest Phones
One of the best phones created by Sony Ericsson, is the G502 phone. Sony has established that phones - Entertainment Articles - It's What Is Behind The Scenes That Make Your Movie Viewing Pleasurable
Is there anything that can make or break your entertainment system at home and is something that no - Current Affairs Articles - 2012 Facts
Making sense How can we make sense of this? Each different theory or combination of theories will m - Science & Technology Articles - High-density PCIe Telephony Cards from Telesoft Technologies
With well over two decades of experience in the networking and media fields, Telesoft Technologies i - Science & Technology Articles - IVR Servers from Telesoft Technologies
The interactive voice response server (IVR Server) solution is perhaps one of the most important rec - Education Articles - Old Teachers Learning New Technological Tricks
As technology and teaching methods have progressed, many classrooms have found themselves brighten - Business Articles - A Guide To Streamlining Office Technology
Any modern office will likely have the following core contents: desks, chairs, networked computers
Most viewed articles in this category:
- The Bat in Bible and Quran
One of the inherited doctrines of mankind is that the Quran is quoted or borrowed from the Bible.The - The Rabbit in Bible and Quran
The Bible says that the Rabbit is a ruminant animal while the sciences say that the Rabbit is not a - The Semen in Bible and Quran
One of the expanded dogmas of mankind is that the Quran is quoted or borrowed from the Bible. This c - The Iron in Bible and Quran
Before dealing with the topic of the Iron in Quran versus Bible versus sciences, it is essential to - More and More, Scientists Recognize That Foods Can Heal
Folk remedies that used to be written off as old wives' tales are now being acknowledged by scientis - Streamlining the Management of Print Spooler Output in an Oracle Applications Environment
The customer associated with this case study is a large, multi-national manufacturer of product - Manapol: Why Should I Use It?
Manapol® Why Should I Use It? "Upon entry to the cells, mannans can activate the ma - The Sleep in Bible and Quran
Before dealing with the topic of the Fly in Quran versus Bible versus sciences, it is essential to r - What Types of Sharks Lived Millions of Years Ago?
The first cartilaginous sharks appeared 370 millions years ago. Their size, their appearance and the - How are Cinematography and Memorabilia Related to Sharks?
Sharks have influenced both cinematography and its memorabilia through the years. From Jaws the movi