Quantification of carbon, nitrogen and bacterial biomass in the food of some penaeid prawns

Abstract

The proventriculus contents have been analysed in five species of penaeid prawns, Penaeus plebejus, P. esculentus, P. merguiensis, Metapenaeus bennettae and Trachypenaeus fulvus. Measurements of organic and inorganic carbon, protein and bacterial biomass show that these prawns are omnivores, feeding in an opportunistic manner. Most proventriculus contents contained about 100-150 mg organic C/g dry weight, of which 10-20% was bacterial C. The muddy sediments, over which the prawns were feeding, contained from 6 to 30 mg C/g dry weight with 6-16 % bacterial C. A sandy seagrass flat contained 2 mg C/g dry weight with 30% bacterial C. Detritus was sometimes the main food item, bacteria constituting up to 30 % of organic C in the proventriculus. Foraminifera, bivalves and crustaceans were important food items in some prawns. Low bacterial biomass, coupled with high CaCO₃ and high protein content (about 40 % of organic matter) indicate that the fragments of animal skeletons are from live prey eaten by the prawns. Little difference was noted between species of prawns in their food preferences.