Studies on the chronic soft-shell syndrome in the tiger prawn, Penaeus monodon Fabricius, from brackishwater ponds

Abstract

Prawn culture is becoming more widespread in the Philippines. In recent years, prawn production in brackishwater ponds has been adversely affected by a chronic soft-shell syndrome. A field survey of prawn ponds in the island of Panay showed that occurrence of soft-shelled prawns could be predicted with 98% accuracy under poor soil and water conditions in the ponds. Some management practices were also highly correlated with the soft-shell syndrome. Soft- and hard-shelled prawns collected during the survey were analyzed for calcium and phosphorus levels. In soft-shelled prawns, calcium and phosphorus levels were significantly higher in the hepatopancreas, and phosphorus was significantly lower in the exoskeleton than in hardshelled prawns. Chitinoclastic bacteria, Vibrio and Aeromonas, were isolated from soft-shelled prawns but experimental infection with these species to induce soft-shelling gave largely negative results. Laboratory experiments using an organostannous pesticide revealed that a 96-h exposure to at least 0.0154 ppm of the pesticide could result in soft-shelling of 47–60% of the prawns. Soft-shelled prawns were fed various quantities of frozen mussel meat for 4 weeks to find out if soft-shelling could be reversed by dietary manipulation. Successful reversal of soft-shelling, general improvement of shell quality, and best growth and survival rates were observed in prawns fed a 14% mussel meat diet.