Assessment of five shelter types in the production of redclaw crayfish Cherax quadricarinatus (Decapoda: Parastacidae) under earthen pond conditions

An experiment was designed to assess the relative performance of several shelter types on the production of redclaw crayfish Cherar quadricarinatus under earthen pond conditions. Juvenile crayfish with a mean stocking weight of 12.76 g were cultured in 24 net pens at 12.5 m2 within a 0.2 ha earthen pond, and were provided with one of five shelter types or no shelter over 162 d. The various shelter types assessed were: mesh bundles, pipe stacks, car tires, elevated cement/fiber-board sheets, and cement/fiber-board sheets laid flat on the substrate. Crayfish in each pen were fed a formulated pellet diet three times each week. Treatments were assessed on the basis of crayfish growth, survival, harvest biomass and berry rate among females at harvest. There was no significant effect (P > 0.05) of shelter type on growth; however, there was a highly significant effect (P < 0.001) on survival with mesh bundles (75.1%), tires (51.4%), and pipe stacks (43.25%) performing significantly better than the no shelter control (15%). The consequence of equal growth and differing survival among treatments produced significant differences in harvest biomass (P < 0.01). There were also significant differences in berry rate for the different treatments (P= 0.002), and a significant negative correlation of berry rate on survival for those treatments where shelter was provided. This experiment showed that the shelter types provided during pond culture had a significant effect on harvested biomass, primarily through its effect on survival. The efficacy of the mesh bundle shelters may be attributable to the variability in the size of the spaces provided, and the ability of the mesh to separate many individuals relative to the overall volume of the shelter.