The borderline between reduces growth rate and diminished health, on one hand, and overt disease, on the other hand is always very difficult to detect. Therefore, the ability to recognize deterioration in performance during its developmental stages and take corrective action will remain an essential skill of the fish culturist. The problem of this work is tackling of the level of remain food decomposition and nitrogenous product excreted by cultured fish, which can lead to deterioration of water quality in high stocking levels common in fish farming practice systems. Among the methods used in assessing the effect of water quality in fish, was the blood evaluation. This work has been written as standard text and is intended for students in aquaculture and veterinarians whose remit includes diagnosis or management of fish diseases and for those fisheries scientists who need to know more about fish problems associated with deterioration of water quality.It is relevant also to workers in the pharmaceutical industry concerned with the development of products aimed at the fish health market and to monitors of human foodstuffs and public health.