Aquaculture International 4, 361-376 (1996) The effect of dietary protein source on growth and carcass composition in juvenile Australian freshwater crayfish Paul L. Jones, Sena S. De Silva, and Brad D. Mitchell School of Aquatic Science and Natural Resources Management, Deakin University, Warrnambool, PO Box 423, Victoria 3280, Australia. A feed trial was conducted for 12 weeks on juvenile Australian freshwater crayfish (Cherax destructor) (mean weight (SE) 0.82 (0.02)g) maintained on five isoenergetic diets with a protein content of 30%. Diets differed in the primary source of protein used, with meat, snail, soybean, yabby, and zooplankton meals comprising the major protein ingredient, varying from 56-60% of total protein. Mean percentage weight gain per day ranged from 7.57% (yabby meal diet), to 9.42% (snail meal diet). No significant difference occurred in mean weight, percentage weight gain, specific growth rate (%), or survival among diets. A maximum size of 16.44g was attained on the yabby meal diet. Largest mean weight was 8.27g on the snail-based diet. Food conversion ratios were all good, with a minimum value of 0.95 recorded for the snail-based diet. Initial food consumption per day was approximately 5% of mean animal weight, decreasing to around 2.4960, and is collectively described by a power curve. Protein retention ranged from 29.57% in the zooplankton meal diet to 41.15% in the snail-based diet. Carcass composition was influenced by feed type, with the most marked difference occurring in carapace colour. Animals fed the zooplankton-based pellets developed the strongest pigmentation. Recommendations are made for including certain protein-based ingredients in manufactured yabby diets. KEYWORDS: Australian freshwater crayfish (Cherax destructor), Carcass, Food, Growth, Pellet stability, Protein INTRODUCTION The polytrophic, omnivorous feeding behaviour of freshwater crayfish (Lol'man and Magnuson, 1978; Momot et aL, 1978; Sokol, 1988; D'Abramo and Robinson, 1989; Tacon, 1993), suggests they have the capacity to utilize a wide variety of natural foods. This may permit a range of animal and plant-based ingredients to be effectively incorporated into practical diets, on a low cost basis. As protein is usually the major cost-limiting factor in artificial diets used in aquaculture (Goddard, 1988; Shiau and Chou, 1991; Ackefors et aL, 1992; Ali, 1992), it has been selected as the basis of this study. In previous work on the yabby, Cherax destructor (Jones et aL, 1996), and other decapods (Akiyama, 1988; Reigh et al., 1990; Lochmann et al., 1992; Reigh et al., 1993), soybean meal was identified as a useful source of protein that can effectively replace fishmeal to some extent. An optimum soybean meal inclusion level of 0967-6120 © 1996 Chapman & Hall