Size rank and growth potential in redclaw crayfish (Cherax quadricarinatus):: are stunted juveniles suitable for grow-out?

Considerable size variation emerges at an early stage among redclaw (Cherax quadricarinatus) juveniles. In order to explore whether juveniles from different size fractions of the same population differ in their growth potential, they were reared individually, in the absence of social effects. In the first experiment, post-release siblings were reared for 5 weeks and then categorized into three size fractions: small, med-sized and large. Subsequently, juveniles of each size fraction (n=24, 18, and 18, respectively) were reared in individual cells for 46 days and their moult increments and moult intervals were compared. In addition, the growth indices of the med- and large-sized juveniles were compared with those of juveniles from other broods that were similar in age and size but belonged to a different size fraction, in order to separate the effect of absolute size from that of size rank. In a second experiment, juveniles from the small-, med- and large-size fractions (n=21) of a commercial nursery-reared population were individually reared for 14 weeks and their growth indices were compared. Survival of individuals from the small-size fraction was low, particularly in the first experiment, and increased with fraction size. However, small-sized juveniles did not show reduced growth potential and even grew at a faster rate than large-sized juveniles. The results indicate that social interactions plays an important role in the development of size variation, and that small juveniles have the potential to grow rapidly when reared in individual compartments. Overall, the size rank was a poor predictor of growth potential.