Crayfish growth rates can vary considerably among individuals from the same brood, and social dominance hierarchies in crustacean species occur frequently. These hierarchies can reduce growth and survival when rearing communal groups. Size-grading and single-sex culturing are the methods used to combat this. A 160-day experiment took place on 288 young-of-the-year captive-born Austropotamobius pallipes, within a closed-circuit, indoor aquaculture facility. Crayfish were reared in three treatments (a) equal numbers of large males + small females (LMSF); (b) equal numbers of small males + large females (SMLF); (c) individuals of the same size, equal sex ratio; plus two control groups of single-sex, same sized individuals. Female survival in the LMSF was significantly reduced (52.8%, SD = 20.7%), whereas overall survival in all other groups was high (83.1%, SD = 15.1%). Male growth (6.3 mm, SD = 0.6 mm) was greater than female growth (4.9 mm, SD = 0.9 mm) across all groups. Cheliped autotomy was significantly greater (8.8%) in males (26.7%, SD = 8.9%) than females (17.9%, SD = 2.7%). This study suggests that young-of-the-year juvenile male A. pallipes grow faster and are more aggressive than females. Large males will suppress and reduce survival in smaller females whereas small males, when housed with larger females, will still grow faster than the females. We suggest that it is sex and not size that is the main factor that causes dominance hierarchies and growth suppression within juvenile A. pallipes. Maintaining juvenile A. pallipes in single-sex groups is optimal to ensure high survival and growth rates.
- cheliped autotomy