Dietary habits of a large, long-lived endangered Australian percichthyid, the eastern freshwater cod Maccullochella ikei

Abstract

The diet of the endangered eastern freshwater cod Maccullochella ikei Rowland, 1985 was studied over 2 consecutive years in the Mann and Nymboida River system, Australia, to determine summer and winter feeding habits. Food items were extracted using non-destructive gastric lavage. In total, 268 M. ikei were gut-flushed over the 2 yr of the study; 191 contained at least 1 food item. A large variety and broad size range of items were recovered, from small aquatic insects to relatively large terrestrial animals. We found significant differences between the food items consumed by M. ikei in summer and winter. Seasonal differences related to the increased occurrence of crustaceans, small fish and terrestrial animals in the diet of M. ikei during winter, and more aquatic insects and molluscs in summer. Food items differed significantly among size classes, with larger M. ikei consuming fewer crustaceans and more large fish and terrestrial animals. Our study revealed that M. ikei displays high plasticity in seasonal dietary habits, changes diet and foraging tactics as it grows, and appears to not always consume what would be considered optimal forage. While many of the issues surrounding the conservation of M. ikei ini- tially appear to be localised, aspects of its biology including its dietary habits also have context across broader scales.