Ecosystem perspectives on management of disease in shrimp pond farming

This paper reviews and discusses, from an ecological perspective, the cause s behind the development and spreading of pathogens in shrimp aquaculture. The risk of disease in shrimp fanning often increases with culture intensit y and high stocking densities, and when polyculture is replaced by monocult ure. High pond densities will facilitate the spread of pathogens between po nds. Shortage of clean water supply and insufficient waste removal lead to overloading of metabolites, environmental degradation, and to the shrimp be coming stressed by bad water quality, and thus more prone to becoming affec ted by disease. Excessive fluctuations in abiotic factors like oxygen, sali nity, and temperature may also increase stress and susceptibility to diseas e. The location of farms in mangrove environments can lead to acidification that may directly, or indirectly, through release of heavy metals from the sediments, lower disease resistance. The use of hatchery-reared larvae wil l increase genetic uniformity and thus disease risk in comparison to the co llection of wild larvae where selection has already favored the most viable individuals. Global and regional transportation of seed larvae and broodst ock will facilitate the spread of pathogens. Apart from the above factors, which are all dependant on the farming itself, contamination by pesticides and pollutants from agriculture and industrial activities may lower disease resistance of the shrimp, especially if combined with other environmental factors. We show that shrimp farming is, to a large extent, dependent on ecological services supplied by nature, and discuss the carrying capacity of shrimp po nd farming from an ecosystem perspective, including aspects like culture in tensity, pond density and sustainability. Since aquaculture is basically a natural ecological process, although in intensive shrimp farming it reaches industrial proportions, it is essential that we do not forget the underlyi ng ecological principles, as this may help us to understand and contribute to the solution of some of the disease problems faced by shrimp farming. (C ) 2000 Elsevier Science B.V. All rights reserved.