Biodiversity

Wednesday, May 10, 2006

THE CARTILAGIOUS AND BONY FISH HAVE DIFFERENT MORPHOLOGIES.

The bony fishes are the fish of the large class Osteichthyes. They are differentiated by a skeleton of a bone. They comprise the majority of the modern fish. They are the most plentiful, varied and multifaceted group of fishes. They are more than other fishes by the ratio of 20 is to 1. They include more species compared to all other combined vertebrates. They are characterised by a bony carcass and slippery, scales that cover their bodies (Frank et al, 1995).


The first bony fishes found had the streamlined bodies. Their fins were well developed. They were characterised by the large eyes and mouths. Their characteristics helped them in evasion. The food they collected helped them to thrive in lakes, streams and the sea. They also developed specific adaptations to unique environments. The oldest bony fishes had thick enamel scales, which in the later forms became lighter. The fins are supported by many slender ray-like bones (Frank et al, 1995).

The early forms were substituted in Mesozoic times by the surviving holeosts that include the garpike and bow fish. The rest of holeosts were replaced in the period of the cretaceous. They were replaced by the teleost ray fins. This group of fish include all almost all the living fish. The choanichthyes include the lung fish. The fins seem to be supported by a strong bony axis. The nostrils open into the mouth (Frank et al, 1995).

The (Chonndrichthyes) cartilaginous are the fish that have only cartilage as hard connection tissue. The cartilage is a type of impenetrable connective tissue. It is composed of fibres. Those fibres consist of collagen and elastic fibres. They also consist of matrix and cells called chondrocytes. The chondrocytes are dispersed in the matrix. They are the only cells available in cartilage. Their functions are to generate and maintain the matrix of the cartilaginous (1).

The cartilage is found in the joints, rib cage, and the ear, the nose, in the throat and between invertebral disks. The function of the cartilages is to provide framework to the beginning of the bone deposition. It seems as if the cartilage has three types namely, hyaline, elastic and fibrocartilage. The hyaline type of cartilage can be found lining bones, especially in the joints and inside the bones. The hyaline found to be the centre for the growth of the bone (1).

The bones of animals are collectively known as the skeleton. The bones and the cartilage seem to have derived from the mesoderm. They are having different composition. The cartilage was found to have formed by the condensed mesenchyme tissue. This tissue differentiates the cartilage into chondrocytes. This further secretes the materials that formed the matrix (2).

It seems as if they were two different types of growth that took place in cartilage, namely the appositional and the interstitial. The appositional found to have increased the diameter of the cartilage. The interstitial found to have increases the mass of the cartilage and occur within (3).

The cartilaginous fish do not have the true bone, while the bony fish have the true bone.
References:


[1].The wikipedia contributors, Coordinated Universal Time [Internet], Wikipedia, The Free Encyclopedia; 2006 May 08, 15; 00 UTC [cited May 2006]. Available from: http//en.wikipedia.org/wiki/Cartilaginous.

[2].The wikipedia contributors, Coordinated Universal Time [Internet], Wikipedia, The Free Encyclopedia; 2006 May 08, 15; 30 UTC [cited May 2006]. Available from:
http://en.wikipedia.org/wiki/Bone.

3. Frank H.T, Herbert S, Paul R. (1965) Fossils, a guide to prehistoric life. Page 136 – 137.

Ms Evelyn Maleka

CILLA CSIR

P.O. Box 395

Pretoria,

0001

Tel: (012) 841 2133

Fax: 012 842 7024.

Email:emaleka@csir.co.za

http://malekaevelyn.blogspot.com/

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