Idiopathic muscle necrosis in the freshwater prawn, Macrobrachium rosenbergii de Man, cultured in Thailand

. A mass mortality of up to 60% per tank occurred in 28‐day‐old Macrobrachium rosenbergii postlarvae cultured under intensive conditions in a hatchery in Thailand. Grossly affected prawns displayed a diffuse ‘milky’ white body opacity; histologically and ultrastructurally, segmental myofibre (myofibrillar and sarcoplasmic) necrosis unassociated with any infectious agents was observed, and was diagnosed as idiopathic muscle necrosis. Avoidance of overstocking and increased dissolved oxygen in tank water have proved effective in preventing subsequent recurrences of the condition.