Effect of stocking density on growth, survival and yield of juvenile redclaw crayfish Cherax quadricarinatus (Decapoda: Parastacidae) in gravel-lined commercial nursery ponds

Abstract

Studies evaluating the effect of stocking density on growth, survival and yield of redclaw crayfish Cherax quadricarinatus have been limited to grow out stages. In this study, an experiment was conducted to assess such effects by stocking 5, 6, 8, 11 or 20 juveniles m −2 in gravel-lined nursery ponds (2500 m 2 each) of a commercial farm in Ecuador, and to determine the feasibility of obtaining a minimum size of 25 g of crayfish after 80 days of nursery stage maintenance. Shelter to cover 50% of the initial population in each pond was provided. Fertilizer and a pelleted ration were used to stimulate growth of redclaw crayfish. There were significant differences in final weight, survival and yield among stocking densities. Significant inverse linear relationships were observed for final weight and survival, in relation to density level ( P<0.05, R 2=0.83 and R 2=0.74, respectively). Stocking at 11 specimens m −2 (or lower rates) permitted the minimum size of 25 g to be obtained. Yield was directly related to density ( P<0.05, R 2=0.93). No evidence for feed conversion ratio being affected by density was found. Growth varied during the trial and the estimate of a single, overall instantaneous growth rate or a specific growth rate, using the exponential equation, was inadequate. A model proposed in this study allowed a satisfactory description for comparing growth curves among treatments. The model exhibited desirable, close-to-linear estimation properties of parameters, and invariance tests showed that density significantly affected values of its parameters ( P<0.05). Uniform and acceptable water quality conditions in all treatments indicated that the effect of stocking density in production of crayfish was most probably exerted by non-aggressive interactions or behavioral factors of the individuals. Results of the experimental trial were acceptable for management of redclaw crayfish culture in Ecuador, and suggest that further improvement in growth and survival at high densities could be achieved by providing more shelter than used in this study.