Food habits of the freshwater catfish, Tandanus tandanus Mitchell, in the Gwydir River, Australia, and effects associated with inpoundment of this river by the Copeton Dam

Abstract

The composition of the diet of T. tandanus was investigated in the Gwydir River before and during inundation of the river by the Copeton Dam. Decapods (Macrobrachiurn australiense and Chevax neopunctatus) were the most important component of the diet by weight, followed by chironomids, fish (Hypseleotris klunzingeri) and miscellaneous aquatic invertebrates. Although fish have not previously been recorded in the diet, they were found to be very important in the diet of small catfish (40% by weight). Ontogenetic changes in the diet were pronounced with a general progression: Entomostraca-Diptera-fish-Decapoda. There was a tendency for larger fish to prefer larger prey. A direct and significant relationship was observed between the size of catfish and the size of M. australiense and C. neopunctatus eaten.

Investigation of the seasonal variation in the composition of the diet revealed that M. australiense was the most important food item in summer and chironomids were most abundant in winter. During the filling phase of the dam a high proportion of terrestrial organisms (up to 52%) were included in the diet. Successional blooms of species, not observed in the diet previously, accompanied stabilization of the water level; these included pulmonate snails and dipterans associated with a massive build-up of floating hydrophytes.