لخّصلي

Fishes, the most numerous vertebrates (around 20,000 species out of an estimated 40,000 vertebrate species), exhibit vast diversity in size and shape, ranging from the 21m whale shark to the <15mm pygmy goby. Inhabiting all aquatic environments globally, they are crucial for human sustenance, providing protein and economic benefits. However, overfishing and habitat destruction necessitate the study of fish biology. Understanding fish population dynamics—growth rates, reproduction, mortality, diet—is vital for sustainable fisheries. Fish morphology, intrinsically linked to lifestyle, is fundamental to analyzing organism variation and its relationship to environmental factors, as noted by Grant and Spain (1977). This knowledge enhances both academic understanding and the efficiency of aquaculture management.

rtebrate that breathe with gills and swimming by fins.
Fishes are the most numerous of the vertebrates. The number of species is around 20000, while, the vertebrates are estimates by 40000 species. Fishes are different in shapes and sizes. The whale shark attains lengths near 21 m and 25 tons, while, the pygmy goby attain lengths less than 15 mm. Fishes occupy all water regions in the world and all habitats of water. Fish have great significance in the life of mankind, being an important natural source of protein and providing certain other useful products as well as eco- nomic sustenance to many nations. The gradual erosion of commercial fish stocks due to over -exploitation and alteration of the habitat is one reason why the science fish biology came into existence . It is a well-known fact that the knowledge on fish biology particularly on mor- phometry, length-weight relationship, condition factor, reproduction, food and feeding habit, etc. is of utmost important not only to fill up the lacuna of our present day academic knowledge but also in the utility of the knowledge in increasing the technological efficiencies of the fishery entrepreneurs for evolving judicious pisciculture management.
For developing fishery, it is necessary to understand their population dynamics- how fast they grow and reproduce, the size and age at which they spawn; their mortality rates and its causes, on what they prey upon along with other biological processes. There are many isolated disciplines in fish biology, of which the study of mor- phology is inseparably related to study of the mode of life of the organism. It fact, the size and shape are fundamental to the analysis of variation in living or- ganisms ( Grant and Spain, 1977) and morphological variations even in the same species most often related to the varied environmental factors