Diet and feeding in the freshwater crayfish, Euastacus spinifer (Decapoda: Parastacidae), from the Sydney Region, Australia

Detailed analyses of gut contents, and field observations of feeding behaviour, clearly indicate that Euastacus spinifer is an opportunistic omnivore; diet does not vary with size, age or sex and much of the food is terrestrial in origin. The bulk of the diet comprises partly decomposed woody materials, but decomposing angiosperm macrophytic material is also consumed with occasional diatoms; small aquatic animal prey are actively hunted at times. It is suggested that nutrients are largely derived from fine organic particles associated with detritus, with supplements from scavenging and predation. The common browsing feeding pattern is not planned or premeditated. A variety of materials can be cropped or gathered in different ways and food particles of widely disparate size are manipulated. The periodic hunting is a premeditated activity involving deliberate stalking of mobile prey and rapid ambush. The occasional bulldozing mode may be a response to scarcity of food but details of preferred food particle size and contributions of specific sources remain unknown. Preliminary trials demonstrate that both hepatopancreatic fat content and protein concentrations in gastric fluid show wide individual variation, suggesting fluctuating feeding success. Future trials, to test for an index of nutritional state, should be of short duration, with larger samples at a single moult stage. Factors suggested as contributing to variation in feeding success among wild populations include seasonal changes and food availability.