A contribution to the food and feeding habit of the threadfin Galeoides decadactylus

Abstract

Previous literature on the biology of the threadfin Galeoides decadactylus (Bloch, 1795) and the different methods of food analysis are reviewed. Against this back-ground, new results obtained on food and feeding habit are presented. All specimens sampled belong to the first 2-year classes (Longhurst, 1965). Fishes of the same length are shown to have a wide range of weight, attributable to the effect of spawning and sex change; G. decadactylus is a protandrous hermaphrodite (Longhurst, 1965). Feeding intensities and condition factors are generally high, and show a direct relationship with the size and, consequently, sex, of the fish. The comparatively low percentage of empty stomachs recorded is attributable to the rather more favourable feeding conditions existing in inshore waters where the fishes were caught. G. decadactylus feeds mainly on small seasonally alternating varieties of crustaceans and young fish. Analysis of the composition of the fish food reconciles the apparently contradictory results obtained by Monod (1927), Cadenat (1954) and Longhurst (1957, 1960). The absence of certain common demersal food items such as mud and cephalopods in the stomach of G. decadactylus leads to the conclusion that the fish is selective in its feeding habits.