Environmental management of shrimp farms in Asia to promote healthy shrimp and reduce negative impacts

Abstract

Shrimp production in Asia ranges from extensive culture of Penaeus monodon to super- intensive culture of Litopenaeus vannamei. Farms often are small but there also are large farms, a few of which produce more shrimp than some shrimp producing countries in the Western Hemisphere. Production technology varies from primitive techniques to the most modern methods. There is a trend towards greater biosecurity by using disease-free broodstock, disinfection of source water and reduction in water exchange. Mechanical aeration allows for great increases in production, but most aerators used in Asia are low in efficiency compared to aerators used in the United States. Aerators cause much erosion in earthen ponds. Lined ponds allow for greater aeration and two to three times more shrimp production per hectare than in unlined ponds. Aeration requirements should be based on feed conversion efficiency, feed BOD, target DO concentration and aerator efficiency. Energy use in aeration is a major expense, often amounting to US$0.40 or more per kilogram shrimp. Aerator efficiency could be improved through changes in aerator design. Moreover, a reduction in daytime aerator use when water usually contains plenty of dissolved oxygen could reduce electricity costs. At some farms, organic sediment is removed from lined ponds during the production cycle to lessen oxygen demand and increase the proportion of dissolved oxygen added by aerators available to shrimp. Biological oxidation of ammonia nitrogen in lined ponds causes total alkalinity concentration to decline and lime applications should be made at frequent intervals in proportion to feed input. The usual amount of lime needed is about 0.3 to 0.5 kg CaCO3 equivalent per kilogram feed. There is no evidence that water quality in ponds can be improved through additions of zeolite, coagulants, microbial products (sometimes called probiotics) and other amendments. There is increasing attention on implementation of better management practices to lessen negative environmental impacts of shrimp farming and comply with eco-label certification programs. ____________________________________________