![]() | Only 14 pages are availabe for public view |
Abstract a) The knowledge of fish fanning dates back to several thousand years according to old chinese writings and Egyptian bus-reliefs. This explains the importance of fish as a food source of high protein content. The protein of fish origin is of high biological value for human being as it is very essential for growth and maintance of vital functions. Moreover, certain localities of the world depend mainly on the fish as a source of animal protein, so it would be wise economically to cultivate such important source of protein to meet the dietary need of the expanding population. Nile tilapia (Oreochromis niloticus) plays a good role in the intensive, semi-intensive and extensive artifical breeding culture programmes in different locations in Egypt (Badran and Eissa, 1991). The fish culturing, especially the intensive culture, acts as predisposing for appearance and spreading of many fish diseases. Fish diseases due to bacterial infection are considered one of the major problems in aquaculture particularly in the intensive culture (Austin and Austin, 1987). Most of the bacterial causative agents associated with such diseases are naturally saprophytic organisms, widely distributed in the aquatic environment (Frerichs and Hendrie 1985). Only a comparatively few species are classified as true obligate pathogens. Both classes of organisms, however, may be present on the external body surface or within the tissue of apparently healthy fish. Stress factors such as poor water quality, temperature changes, over-crowding and parasitism allow these bacteria to become pathogenic to fish (Badran and Eissa, 1991) .. 1 |