Health and diseases in aquaculture
Diseases of aquaculture species caused by parasites and infectious pathogens have attracted the attention of veterinarians and fish biologists from the early days of aquaculture investigations. A number of prophylactic and curative measures have also been suggested, although many of the chemicals have not been cleared for use in some countries. As will be discussed later, there are a number of diseases for which there are, as yet, no known remedies. With increasing investments in aquaculture and closer examination of factors that contribute to the risks faced by an aquaculturist, the concept of integrated health protection measures has developed in recent years. Similarly, experience of fish farming in the tropics has brought into focus the public health aspects of fish farm development and the possible role of aquatic farming in the spread of communicable human diseases. The extensive introduction and transplantation of aquaculture species occurring at present have clearly shown the need for regional and international cooperation in controlling the spread of communicable diseases and implementation of mutually acceptable measures for the purpose. Thus fish health and disease control are now viewed from different angles, that include environmental protection and pollution control, human health and epidemiology, site selection and culture technologies, monitoring and sanitation of aquaculture facilities, diagnosis and treatment of diseases of cultured species, avoidance of nutritional diseases, prevention of epidemics of mortality in culture facilities, formulation and implementation of regulatory measures to control national and international spread of communicable diseases, development of diseaseresistant strains through genetic selection and hybridization and individual and mass immunization of cultured species.
Undoubtedly the research, development and regulatory measures needed for an integrated health management programme in aquaculture involve considerable expertise, organization and expense. Both the State and the aquaculture sector will have to share the responsibility for the successful implementation of such a programme. Being probably the most important risk factor in an aquaculture enterprise, such a programme will have direct relevance to the development of a risk insurance system to protect the farmer from unavoidable losses. While the need for these measures is readily recognized, the low magnitude of the industry at present and uncertainties about the extent to which it can develop and contribute to the overall national economies have prevented its realization in most countries. There is now, however, a greater recognition of its importance among aquaculturists. For example, in Asia disease problems were considered to be of only secondary importance when extensive farming was the most common practice. With the adoption of semiintensive and intensive systems, the occurrence of several forms of diseases and consequent mortalities have significantly increased. Similarly, improved expertise and facilities in disease diagnosis have led to the identification of several previously unknown pathogens and disease conditions. Consequently, greater efforts are now being made to diagnose and control disease conditions in the region.