The role of microorganisms in aquaculture ponds

Microorganisms have major roles in pond culture, particularly with respect to productivity, nutrient cycling, the nutrition of the cultured animals, water quality, disease control and environmental impact of the effluent. Management of the activities of microorganisms in food webs and nutrient cycling in ponds is necessary for optimising production, but the objectives will differ with the type of aquaculture, the species cultivated and the economics. Unlike the pastoralists who fertilise and seed pastures with selected species, fish farmers only fertilise ponds and hope that useful species of algae, bacteria and other microorganisms will develop. Factors controlling the composition and development of blooms of both desired and undesirable species of algae and bacteria need to be investigated. Analysis of the complex food webs in ponds, combined with measurements of primary productivity, C cycling through bacteria, zooplankton and meiofaunal biomass changes and nitrogen cycling will provide the basic data for generating a model to describe and predict fish productivity in ponds. Algae and bacteria have often been regarded as single groups of organisms by aquatic biologists, but there is a great diversity of species of each, with different roles and interactions in their ecosystems. This fact, together with the many environmental variables, makes it difficult to develop a single comprehensive, predictive model as a tool for managing food webs and water quality in ponds, but small models specific to given pond systems or stages of grow out are likely to be successful