Organic pollution resulting from excess feed and metabolite build-up: Effect on Penaeus monodon postlarvae

Abstract

Penaeus monodon postlarvae, PL, with mean weight and mean total length of 0.57 mg and 6.5 mm respectively, were stocked in aerated aquaria at 20 litre⁻¹ of seawater. They were fed minced shrimp meat at rates of 10, 50, 100, 250, and 500 mg litre⁻¹. Aquaria with diatoms as feed served as control. Growth and survival rates were examined at each feeding level. Water quality parameters measured were dissolved oxygen (DO), ammonia (NH₄-N) and nitrite (NO₂-N) nitrogen concentrations and 5-day biochemical oxygen demand (BOD5). Growth of postlarvae was similar at all feeding levels and greater than the controls. Survival rate at the lowest feeding level was better but not significantly higher (P > 0.05) feeding level of up to 50 mg litre⁻¹ proved to be satisfactory for both growth and survival. Beyond this level, accumulation of organics, low DO, and build-up of metabolites caused a rapid deterioration in water quality. Even at sub-lethal levels a combination of adverse environmental conditions imposed stress upon the cultured organisms and decreased survival rates.