Combined effects of temperature and diet on growth and survival of YOY crayfish: a comparison between indigenous and invasive species.

During a three-month rearing period we compared the (1) survival rate, (2) growth at moult, (3) number of moults, and (4) overall growth of the young of the year (YOY) of two crayfish species, the indigenous Austropotamobius pallipes and the nonindigenous Procambarus clarkii. One hundred twenty YOY of each species were reared in different test conditions, i.e., three temperatures (16°, 20°, and 24°C) combined with two different dietary regimes (either animal or detritus food items). The two species showed a number of similarities in their survival rate and growth format. First, in both species, animal proteins appeared fundamental for the YOY growth, because an exclusively vegetal diet significantly slowed growth rate. Thus, the YOY seemed to behave as obligate carnivores, and detritus appeared ineffective in sustaining growth. Then, an exclusively animal diet showed some deficiencies: exoskeleton appeared pale in its colour when the diet was composed of animal items only, possibly because carotenoids were lacking. Third, an increase in the temperature caused a decrease in both survival and growth rate, because it determined a reduction of the moult increment in both species. Differences between the two species were that the nonindigenous crayfish showed a significantly higher tolerance of elevated temperatures, and growth was significantly faster in P. clarkii than A. pallipes, being approximately double when the crayfish were reared with an animal diet. Together with other behavioural and ecological properties, these features make P. clarkii more competitive than A. pallipes in disturbed habitats and areas which are subject to man-induced modifications.