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The first action that a farmer usually takes when faced with a population of sick or dying fish is to call a veterinarian or fish pathologist. If on examining the fish no recognisable disease organism is found (ie. bacteria, virus or parasite) then the incriminating finger is usually pointed toward the diet of the fish or to water quality as being the cause of the problem. However, on calling the local feed manufacturer the sales representative more often than not tries to place the blame on poor water quality or on other non-feed related factors. Throughout the above chain of events the farmer generally still remains in the dark, continues to suffer heavy fish mortalities, and is desperately in need of an unbiased opinion and solution to his or her problem. Although the above scenario is gradually improving with the development of modern disease diagnostic laboratories, nutritionally related ‘disease’ problems still remain a largely uncharted territory, veterinarians usually being too busy coping with their routine disease diagnostic duties, and nutritionists usually not being interested nor scientifically qualified to undertake pathological analyses or make judgements on pathology related issues. Clearly, fish pathologists and nutritionists will have to work in tandem in the future if rapid strides are to be made in the emerging and commercially important field of nutritional fish pathology; nutritional fish pathology being concerned with the study of those health disorders/ailments (often inappropriately referred to as ‘diseases’) which result from nutrient deficiencies or dietary imbalances.

In contrast to extensive and semi-intensive farming systems were fish obtain all or part of their dietary nutrient needs from naturally available pond food organisms, fish maintained under intensive culture systems rely totally on the provision of a nutritionally complete diet throughout their life cycle. For many farmed fish the development of commercial feed rations has proceeded despite the lack of reliable published information being available on their dietary nutrient requirements. In view of this paucity of information it is perhaps not surprising that dietary related pathologies have often arisen from specific nutrient deficiencies and imbalances under practical farming conditions. The aim of this paper is to summarize the major nutritional pathologies which have been reported within farmed fish.

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