THE MORPHOLOGICAL DIFFERENCES THAT EXIST BETWEEN THE CARTILAGIOUS AND BONY FISH.

The bony fishes are the fish of the large class Osteichthyes differentiated by a skeleton of bone and comprising the majority of the modern fish. They are the most plentiful, varied and multifaceted group of fishes. They outnumber all other fishes twenty to one and include more species as compared to all other vertebrates combined. They have bony skeleton and slimy, scales that cover their bodies.

The first bony fishes had streamlined bodies and well – developed fins. The bony fishes had large eyes and mouths, aids in evasion and food gathering 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. In the actinopterygian forms the fins are supported by many slender ray-like bones.

The early forms were substituted in Mesozoic times by the surviving holeosts that include the garpike and bow fish. Most of the holeosts were also replaced in the time of the cretaceous by the teleost ray fins which included almost all living fish. The lobe fins or choanichthyes include also the lung fish, fins are supported by a strong bony axis and the nostrils open into the mouth.

The (Chonndrichthyes) cartilaginous fish are fish (animals) having only cartilage as hard connection tissue. The cartilage is a type of impenetrable connective tissue. The cartilage is composed of fibres consisting of collagen and elastic fibres, a matrix and cells called chondrocytes which are dispersed in the matrix. These cell types are the only cells available in cartilage and they generate and maintain the matrix of the cartilaginous.

The cartilage is found in the joints, rib cage, and the ear, the nose, in the throat and between invertebral disks. The cartilage functions as the framework provider upon which the deposition of bone can commence. There are three major types of cartilage namely, hyaline, elastic and fibrocartilage. The hyaline type of cartilage is found lining bones in joints and inside bones, serving as the centre for bone growth.

The bones of animals are collectively known as the skeleton. However, both the bones and the cartilage derived from the mesoderm, they have the different composition. The process in which cartilage is formed from condensed mesenchyme tissue that distinguishes into chondrocytes and begins secreting the materials that form the matrix is found to be the Chondrification.

There are two different types of growth that takes place in cartilage, namely the appositional and the interstitial. The appositional increases the diameter or thickness of the cartilage and the interstitial increases the mass of the cartilage and occur within.

References:

1. The wikipedia contributor, the free encyclopaedia [internet] cited PTA, accessed on 08/05/2006, 16:00 available from [http://en.wikipedia.org/wiki/Cartilaginous]

2. The wikipedia contributor, the free encyclopaedia [internet] cited PTA, accessed on 08/05/2006, 15:300 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.