Fish because of the possession of notochord, holes in the
pharynges (throat) called silts or clefts and nerve cord which is dorsally
oriented except in the primitive fishes belong to the phylum Chordata
.
They are the most numerous vertebrate about of which about 20,000 species are known to science. Fish is also of various shapes and forms from the smallest Niamey to 17mm total length to the giant whale shark that measure 15m in heights and 25 tonnes. Fish are poikilothermic cold blooded animals that survive in aquatic environment by the use of gills on the posterior (Ikenweiwe, 2010). Like most animals, the fish has a body which includes the head, the trunk and the limbs. The body has generally an elongated shape. The head, the trunk and the tail follow each other without any separation, which enables the fish to wriggle easily in the water. Limbs are fins.
The body is covered with the skin. The skin itself is covered by a layer of mucus which forms a protective sheath. If a fish is caught and handled roughly or with dry hands, mucus is removed and the skin remains exposed and may be injured by parasites, always numerous in the water. Fish, therefore should always be handled gently, with care and as little as possible. Most fish, except for instance catfish (Siluriformes), have scales under their skin, which cover each other like the tiles on a roof. The number of the scales covering the body of a fish varies only a little and can be used for identifying the different species. Running along the side of the body, it a line of scales which have little pits in them; this line is called the lateral line. The pits are sensory organs and are responsive to changes in pressure in the surrounding water.
The body of a fish is supported by a skeleton which is a bony frame. The skeleton keeps up the shape of the fish, acts as a muscle-holder and protects the internal organs. It is made of the skull bones which keep up the head, the backbone which keeps up the body and the tail, the fin-bones and the arch-shaped bones carrying the gills (Ikenweiwe, 2010).
.
They are the most numerous vertebrate about of which about 20,000 species are known to science. Fish is also of various shapes and forms from the smallest Niamey to 17mm total length to the giant whale shark that measure 15m in heights and 25 tonnes. Fish are poikilothermic cold blooded animals that survive in aquatic environment by the use of gills on the posterior (Ikenweiwe, 2010). Like most animals, the fish has a body which includes the head, the trunk and the limbs. The body has generally an elongated shape. The head, the trunk and the tail follow each other without any separation, which enables the fish to wriggle easily in the water. Limbs are fins.
The body is covered with the skin. The skin itself is covered by a layer of mucus which forms a protective sheath. If a fish is caught and handled roughly or with dry hands, mucus is removed and the skin remains exposed and may be injured by parasites, always numerous in the water. Fish, therefore should always be handled gently, with care and as little as possible. Most fish, except for instance catfish (Siluriformes), have scales under their skin, which cover each other like the tiles on a roof. The number of the scales covering the body of a fish varies only a little and can be used for identifying the different species. Running along the side of the body, it a line of scales which have little pits in them; this line is called the lateral line. The pits are sensory organs and are responsive to changes in pressure in the surrounding water.
The body of a fish is supported by a skeleton which is a bony frame. The skeleton keeps up the shape of the fish, acts as a muscle-holder and protects the internal organs. It is made of the skull bones which keep up the head, the backbone which keeps up the body and the tail, the fin-bones and the arch-shaped bones carrying the gills (Ikenweiwe, 2010).
According to Olatunde (1989), fish constitute 40% of animal protein
intake in Asian countries and about 17% in Africa.
Biologically, it is of fundamental importance in the balance of
nature because it subsists on many organisms feeding on some and being feed
upon by others especially in the aquatic ecosystem and its products are also
utilized industrially as raw materials in animal feeds, fertilizer production, and
iodine containing fish oil and in leather manufacturing industries (fish
skins).
No comments:
Post a Comment