Diet of the Australian grayling, Prototroctes maraena Gnnther (Salmoniformes : Prototroctidae), with notes on the occurence of a trematode parasite and black peritoneum

Abstract

The diet of the Australian grayling was studied based upon an examination of the stomach and intestinal contents of 558 fish taken from the Tambo River, Victoria, throughout 1979. The most frequent food items were the immature stages of aquatic insects such as chironomids, trichopterans, and ephemeropterans, gastropods and abundant plant material in the form of a diatom/organic matrix that occurred in 83% of the stomachs. It is speculated that the grayling's black peritoneum is related to the presence of plant matter in the diet. A total of 120 different taxa was recorded but only 23 taxa occurred in 5% or more of the stomachs. Most stomachs were three-quarters full and mean monthly fullness varied little throughout the year. There was little dietary overlap between summer (when the diatom/organic matrix was of relatively low importance) and the other seasons in all size classes examined. There was significant dietary overlap between the size groups for all seasons except summer. Trematode parsites of the family Opecoelidae occurred throughout the gut in 86% of the specimens. The largest fish had the most parasites, and the incidence of infection was consistently high throughout the year.