Role of pelagic crustaceans in the diet of the longnose lancetfish Alepisaurus ferox in the Seychelles waters

Abstract

The role of pelagic crustaceans in the diet of the longnose lancetfish Alepisaurus ferox was investigated from stomach content analysis of fish collected in the waters surrounding the Seychelles Archipelago in the western Indian Ocean. Crustaceans accounted for 88.4% by prey number and 73.7% by reconstituted mass during the South-West monsoon season. During the North-East monsoon season, crustaceans remained the main prey group and accounted for 63.7% by prey number and 46% by reconstituted mass. There was a clear seasonal pattern with the portunid crab Charybdis smithii predominating during the South-West monsoon season and the pelagic stomatopod Natosquilla investigatoris during the North-East monsoon season. This pattern likely reflects variations in prey availability linked to current movements around the Seychelles Archipelago. Most of the prey consisted of slow-swimming and small individuals, which occur in dense swarms during the pelagic phase of their life history. The dietary trends of lancetfish are consistent with opportunistic feeding on the most abundant prey. They exploit short food chains based on carnivorous crustaceans, and play an important role in the pelagic trophic functioning of the western Indian Ocean.