The crisis in Asian shrimp aquaculture: current status and future needs

Abstract

Summary White-spot disease is a relatively recent but widespread epizootic of cultured shrimp in Asia. This epizootic probably began in China in 1993 and subsequently spread from there to Japan, Taiwan, and the rest of Asia as far as India. Pond-side losses in 1996 in Thailand alone reached approximately 70000 metric tonnes, valued at over half a billion US dollars. For all of Asia, the loss must amount to several billion dollars. The Asian science community reacted quickly to this disease outbreak. Within one year, the causative agent was identified as a bacilli-form virus and within 3 years diagnostic DNA probes had been developed by several groups working in Japan, Taiwan, and Thailand. The virus has been included in the nonclassified virus group and is now generally referred to as white-spot syndrome virus (WSSV). Previous experience with another serious epizootic caused by yellow-head virus (YHV) helped to prime the science community for the advent of WSSV. Using the DNA diagnostic probes developed, many sources of WSSV were identified. The list now includes over 40 reservoir crustaceans and perhaps even aquatic insects. All of the commonly cultivated shrimp in Asia can be infected with the virus and for many, the infection can be deadly. In addition to noncultivated carriers, the postlarvae used to stock rearing ponds have also been found to be potential sources of rearing pond contaniination. Knowledge of the virus and its host species has brought about revolutionary changes in hatchery and farming practice, in order to implement preventive measures. These include the use of polymerase chain reaction (PCR) technology to screen broodstock and larvae, and the widespread adoption of closed or semiclosed cultivation. It is believed that without widespread application of these and other preventive measures, the losses in Thailand in 1996 would have been much higher. The WSSV epizootic has increased the awareness of the shrimp farming industry to the urgent need for further research and development work, if the shrimp industry is to become sustainable. Prime needs include domestication of broodstock leading to breeding programs; a better understanding of shrimp defences against disease; a better understanding of shrimp nutrition; and a better understanding of the shrimp pond environment so that growth can be optimized and negative impacts on the environment eliminated.