Effect of dietary protein level on growth and survival of juvenile freshwater crayfish Cherax quadricarinatus (Decapoda: Parastacidae)

Protein requirements of juvenile freshwater crayfish Cherax quadricarinatus , with initial mean weight of 1.08+/-0.34 g, were studied. Juveniles were fed experimental diets containing seven levels of crude protein (CP) (20, 25, 31, 37, 43, 49, and 55%) and 18.73-21.45 kJ g(-1) of gross energy. The highest mean weight and specific growth rate (SGR) (P<0.05), with values of 9.6 g, and 3.64% day(-1) , respectively, were achieved by feeding a diet of 31% CP. This diet resulted in a survival rate of 80% over 60 days of culture at 27degreesC. The higher protein level tested (55% CP), yielded a significantly (P<0.05) lower mean weight of 6.4 g. However, there were no significant differences in SGR among the 20, 25, and 49% CP diets. Feed Conversion Ratio (FCR) was close to 1 for all treatments except the lowest (20%) and highest (55%) CP. Optimum protein requirements were estimated by fitting mean weight gain data to a quadratic model (y=1.142+0.484-0.0071x(2) , r(2)=0.952, P<0.05). Optimal growth occurred with 34.2% CP, but the results suggest that optimum protein level for 1-g juvenile C. quadricarinatus is 31% in least-cost diets. The information obtained will contribute to the formulation of diets that will enhance production of C. quadricarinatus .