The biology of a landlocked form of the normally catadromous salmoniform fish Galaxias maculatus (Jenyns). V. Composition of the diet

Abstract

The composition of the diet of a landlocked form of the normally catadromous stream-dwelling fish Galaxias maculatus from Lake Modewarre in south-western Victoria was studied using a new method of stomach contents analysis based on the principle of ranking. The overall diet of this landlocked fish was found to consist mainly of amphipods, chironomid larvae, and copepods (basic food types), with other groups of crustaceans (cladocerans and ostracods) and insects (trichopteran and zygopteran larvae) being of lesser importance (secondary food types), and a few other incidental food types occurring in only small amounts. The diet of this landlocked form thus consists mainly of crustaceans, in contrast to that of the stream-dwelling form which comprises mainly insects. There was a change in the pattern of feeding in the landlocked fish with growth, the smaller fish eating more of the smaller planktonic and the larger fish more of the larger littoral-benthic food organisms. Amphipods were the dominant food type during all seasons except autumn, when copepods were dominant. Cladocerans were also important when they bloomed in summer, and chironomid adults when they swarmed in autumn. Selection coefficients indicated that those food types which were dominant in the diet were actively selected and those that were unimportant were avoided. This landlocked galaxiid was found to share most of the available food resources with the other four fish species found in the lake, and can be broadly classified as a euryphagic carnivore.