Effect of dietary protein content on growth performance, feed utilization and carcass composition in the Australian freshwater crayfish, Cherax albidus Clark and Cherax destructor Clark (Decapoda, Parastacidae)

Cherax albidus (A) and Cherax destructor (D) male juveniles (mean weight 0.95 ± 0.03 g) were reared for 20 weeks on isoenergetic diets containing 150 g kg -1 protein (A15, D15) or 300 g kg -1 protein (A30, D30). Mean weight, percentage weight gain, and specific growth rate (%) were substantially higher for both species on the 300 g kg -1 protein diet. Mean percentage weight gain ranged from 2.39% day -1 (D15) to 17.59% day -1 (A30). A maximum weight of 33.81 g was attained by C. albidus on the higher protein diet. The most effective utilization of food was observed in C. albidus when fed the higher protein diet (food conversion ratio, 0.79; protein efficiency ratio, 4.21; apparent net protein utilization, 44.64%). Carcass composition was influenced by feed type. The higher protein diet resulted in an increase in carcass protein and ash and a decrease in carcass lipid and energy relative to the low-protein diet (150 g kg -1 protein diet - C. albidus: 37.15% protein, 15.00% lipid, 25.20% ash, 15.55kJ g -1 energy; C. destructor: 38.10% protein, 15.43% lipid, 25.70% ash, 15.65kJ g -1 energy; 300 g kg -1 protein diet - C. albidus: 46.10% protein, 8.71% lipid, 27.36% ash, 14.94kJ g -1 energy; C. destructor: 42.99% protein, 8.56% lipid, 26.44% ash, 14.71kJ g -1 energy). Carcass moisture and calcium were not affected by feed type. The time spent in the intermoult phase of growth was highly dependent on the premoult weight and varied according to diet and to species. A comparison of animals of similar weight ( < 8 g) revealed that elevated dietary protein caused a reduction in the intermoult period by 11 days in C. albidus and 7 days in C. destructor. The moult increment, however, was independent of animal weight, and the highest percentage weight increment occurred for C. albidus fed the 300 g kg -1 protein diet (per cent weight increase; A15, 33.1%; A30, 61.3%; D15, 31.2%; D30, 56.5%). Dietary induced morphological changes were also recorded. Animals of a standard carapace length had significantly larger abdomens (both species) and larger claws (C. albidus) when fed the higher protein diet.