Wednesday, May 10, 2006


Fishes are marine vertebrate animals with back bones, dwelling in ocean, sea and in rivers. They are found under the rocks, in sand and mud. Fishes are divided in to three different classes such as Chondrichthyes, Osteichthyes and Agnatha classes. Agnatha fishes are the small animals that have a mouth like a hole in the head that have no movable parts. These fishes do not have paired fins and they have large gills which serve food filters and respiratory organ.

Chondrichthyes fishes have "strong jaws and also have pairs fins, nostrils, scales, two chambered heart and skeletons made by the cartilage. Their mouth located underside of the head and they use their nose to sense where their food is and same of them use electrosensory system because they are unable to see their food see their food because their eyes are fond on top of their head"( 1) .

Sharks, rays and chimaeras are fishes falls under the class chondrichthyes. The other name of chondrichthye is cartilaginous fish. Their skeleton bones are cartilage meaning that they do not have true bones. They have five to seven gills slits. "They use gills to breathe and during their breath, water passes through mouth, over their gills and out through their gills slits"(1). Their eyes are found at the top of their head and they can not see food as it enters to their mouth (1).

Sharks fish are the one species known as jawed fishes. They also have spiracle behind their eyes at the top of the head. Shakes are the biggest fish, they have "big mouth and they have brown with yellow or white dots on their back" (1). Sharks have five to seven pairs of gills and chimaeras fish have only one pair of gills. "The ghost shark has an external smooth skin and one also have one pair of the external gills opening" (1). Cartilaginous fish have fins which help them not to go under the ocean because they do not have air bladder (1).

Rays fishes have "enlarged pectoral fins; their tails are thin and it ranges from short to long in length" (1). These fishes use their pectoral fins to swim by waving them and sharks their tails to swim. Rays mouth is facing downwards and they have flattened teeth. These fishes "feed themselves on the species that are found at the bottom of the ocean" (1). They change the way of breathing in order to avoid sucking up the bottom mud.

The other name of Osteichthyes is true bony fish. These fishes live in all types of water. This class is divided into two classes which are "Sarcopterygii and Actinopterygii" (2). Class Osteichthyes include "coelacanths and the lung fishes and Sarcopterygii include gars, sturgeons, bow fish and telelosts" (2). The skeleton of the bony fishes made by bone and most of them have a scales. Most of bony fish species have "two sets of paired fins and some have one set of paired fins and some have no fins at all" (2). The species that falls under the class Osteichthyes are snapper, grouper and gurnard fishes. The difference between the bony fishes and the cartilaginous is that the bony fishes have cartilage skeleton bone and the bony fishes have a true bone.


1. Wikipedia contributors. [Internet]. Wikipedia, the free encyclopaedia, 2006 May 09, 10:15 UTC. [Cited May 09]. Available from:

2. Wikipedia contributors. [Internet].Wikipedia, the free encyclopaedia, 2006 May 09, 11:50 UTC. [Cited May 09]. Available from:

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  • You did not really answer the question.

    Please put all your references in the text and in your reference list.

    By Blogger Gwen, at May 22, 2006 10:53 AM  

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