Natural diet of the tiger prawns Penaeus esculentus and P. semisulcatus

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Abstract
Foregut contents of 702 P. esculentus and 426 P. semisulcatus collected from seagrass and offshore habitats in the Gulf of Carpentaria, Torres Strait and Moreton Bay between December 1983 and March 1984 were analysed, and the numerical composition and frequency of occurrence of food items in the diet were compared statistically. Periodicity in feeding was examined in adult prawns collected in hourly 20-min trawls overnight. Gut contents from these prawns were weighed and corrected for size by an empirically derived relationship V = 0.0093l2.818 between gut volume (V, .mu.l) and carapace length (l, mm). The guts of both species were partially filled with food throughout the night. Bivalves, gastropods, ophiuroids, crustaceans and polychaetes were the most abundant food items of both species. Dietary composition overlapped for both species caught in the same trawl, but significant differences (P < 0.05) were found in average numbers of particular items. No significant differences (P > 0.05) in numerical composition or frequency of occurrence of dietary items were found betweenthe sexes of either species. Bivalves, gastropods and crustaceans were the most common items in juvenile and adult P. semisulcatus. Bivalves and gastropods were the most common food items in juvenile and adult P. esculentus. Bivalves were more common in adult than in juvenile P. esculentus. Ophiuroids were found more frequently with larger size of P. esculentus but were constant in all sizes of P. semisulcatus. The only meiofauna found in either species in significant numbers were harpacticoid copepods and these were found mainly in prawns from seagrass beds. P. esculentus and P. semisulcatus appear to eat similar taxa of benthic fauna. Quantitative differences between the diets of both species of prawns captured in the same trawl suggest that they are selective in their diet. Strong regional differences in diet were probably due to differences in the availability of prey.