Tuesday, May 16, 2006


Fish are vertebrate animals that live in water, they have stream lined muscular bodies and they are cold blooded animals. There are three different classes of fish and these include the jawless fish, cartilaginous fish and bony fish. Fish can be found world wide and exhibit amazing adaptations to live in every kind of water habitat. Some fish live exclusively in saltwater, some in fresh water and others in mixed water.

Bony fish are fish that have a skeleton made of bone. They have teeth that are fixed into the upper jaw and have a swim bladder (an air filled sac that helps them with resilience) that opens into the gullet. They are the members of animals called vertebrate. These are animals with backbone. Several examples of this interesting and diverse group are found at sea. They do not have to swim to breath. Most of the fish are bony fish; however sharks, skates and rays are not bony fish.

Cartilaginous fish have the skeleton which is made of cartilage. These include sharks, rays and skates are cartilaginous. Fertilisation of eggs is internal. They have the scales that are placoid and are present all over the body surface. Once their scales are fully formed, they do not to grow but they replaced by new scale once they wear out.

These two fishes differs morphologically, the bony fish are the most diverse and numerous of all vertebrates. They differ from most of the cartilaginous fishes because they have a terminal mouth and a flap covering the gills most of them have a swim bladder which is ordinary use to adjust their buoyancy. Their skin has many mucus glands and is usually adorned with teeth. Most of their skeleton is bone that of sturgeon and few others is largely made of cartilage. In modern cartilaginous fish, lungs or swim bladder-like structures are absent efforts of swimming.

The bony fish have the skeleton with as small as amount of cartilage whereas the cartilaginous fish contains cartage only. Bony fish are able to swim backward and forward whereas the cartilaginous fish only able to swim forward. The cartilaginous fish consist of gill slits but no gills cover and the bony fish are covered with gill slits. The skin characterised of Slipper overlapping scales in bony fishes and in cartilaginous fish the skin is denticle rough sandpaper like placoid scales.

The bony have very good eyesight to avoid being prey. A swimming bladder keeps them floating just like fish on Earth. The unique thing about their swimming bladder is that they can efficiently extract oxygen from the water to fill their swimming bladders. The Cartilaginous fish do not have good eyesight; they make up for this with a good sense of smell. They are common in all the seas of Gump from the polar latitudes to the tropics.


1. Hudson valley community college, 2000, life in the water, [Internet] Online Access: 2006 May 15 10:00 [cited 2006 May 16] Available from:

2. National geographic, 2000, fish of planet, [Internet] Online Access: 2006 May 15 13:00 [cited 2006 May 16] Available from: http://curriculum.calstatela.edu/courses/builders/planets2000/Gump/Limon/AQAnimal3/FISH.html#Bony

Mr Lufuno Mukwevho
CSIR Pretoria
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Email: lmukwevho@csir.co.za
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