Green water microalgae: the leading sector in world aquaculture

Freshwater fish culture is generally considered the largest sector in world aquaculture. Several of the leading species consume green water plankton. This plankton-mostly microalgae (phytoplankton) and also bacteria, protozoa and zooplankton-grows in man-made fertilized water impoundments. The quantity of green water microalgae consumed by fish and shrimp is estimated here at a quarter billion ton fresh weight a year, about three and a half times as much as the entire recognized aquaculture. This estimate is based on the quantities of the microalgae consumed and the efficiencies of their use for growth by the main species in aquaculture. The cost of producing green water microalgae by the aquaculturists-mostly in SE Asia-is low. The populations in green water are biologically managed by the cultured fish themselves. The fish with their different feeding habits help manage the composition of the plankton and the overall water quality as they grow. The aquaculturists further manage green water through simple means, including water exchange and fertilization. Cost is remunerated partially by the income from sales of the fish and partially by bio mitigation services that green water polyculture ponds provide the aquaculturists in treating farm and household waste. A comprehension of the scale and importance of the microalgae sector to world aquaculture should lead to more research to improve understanding of algal population dynamics, growth factors, and efficiency of food chains. The consequent improved control of the plankton's interaction with fish and shrimp production in green water will undoubtedly contribute much to the expansion in production of seafood.