Food selection in freshwater omnivores: a case study of crayfish Austropotamobius pallipes

Abstract

The omnivorous habit and food selection in freshwater macroinvertebrates was investigated in the white-clawed crayfish, Austropotamobius pallipes, a threatened species. First, during an annual cycle we analysed gut contents for vascular plant detritus, moss, amorphous plant material, and animal remains, and evaluated their organic content. Second, we ran preference experiments in the laboratory, in which crayfish had to choose, in the first trial among three vegetal items, in the second trial among three animal prey, and in the third trial between the two preferred items of the previous two trials (i.e. moss and insect larvae). Third, we analysed whether the assimilation efficiencies of different food items affected crayfish food choice. Our results revealed that this species mostly acted as a detritus consumer, obtaining nutrition from the associated microbes, fungi, proto- and metazoans, but also showed herbivorous and carnivorous habits. However, at least when food resources were not limited, crayfish displayed distinct feeding preferences, often ruled by factors other than the nutritional quality and the assimilation efficiency of the selected food.