Unequal division of food resources suggests feeding hierarchy of signal crayfish (Pacifastacus leniusculus) juveniles

Individual food intake of two-year-old signal crayfish (Pacifastacus leniusculus Dana) juveniles (initial carapace length 22.81 ± 1.68 mm and wet weight 3.08 ± 0.67 g) fed semi-moist gelatine-based food were measured four times (days 28, 43, 64 and 91) during a three-month experimental period. Food intake competition results between juveniles from three separate groups was evaluated with the help of feeding ranks that were assessed on the basis of the individual mean values of consumption data from repeated radiography measurements. Signal crayfish juveniles showed high variability in food intake both among juveniles in a group (inter-individual) and within individuals day-to-day variation (intra-individual). This unequal distribution of food resources and its relation to animal size as a main factor to control food intake suggested feeding hierarchy among crayfish juveniles reared communally. This is supported by observed low day-to-day variations in food intake among juveniles with high consumption. The relationship between competition success and size-based dominance were analysed with the change of individual carapace length rank during the experiment based on growth and food consumption data. It seemed that signal crayfish juveniles can raise their rank either by consuming high amounts of food or being very efficient.