Effect of dietary protein level on growth and food utilization in juvenile Murray cod Maccullochella peelii peelii (Mitchell)


S S De Silva, School of Ecology and Environment, Deakin University, PO Box 423, Warrnambool, Victoria, Australia 3280


Murray cod Maccullochella peelii peelii (Mitchell) is a freshwater Percichthyid fish considered to have high culture potential. Growth and feed utilization were examined in a 56-day experiment, in which triplicate groups of juvenile Murray cod (initial weight 21.5 ± 0.03 g) were fed isocalorific diets (gross energy content of about 21 kJ g−1) containing 40%, 45%, 50%, 55% or 60% protein (designated P40, P45, etc.). Final mean weight, percentage increase in weight and specific growth rate (SGR; % day−1) were highest in fish fed the P50 diet. Food conversion ratio (FCR; 1.05 ± 0.04) and protein efficiency ratio (PER; 1.98 ± 0.11) were also best in fish on the P50 diet, but the differences in these parameters from the corresponding values on diets P55 and P60 were not always significant. FCR (Y) was related to dietary protein content (X), the relationship being a second-order polynomial, in which Y = 0.004X2−0.431X + 12.305 (r= 0.95; P < 0.01). The proportions of carcass moisture, protein, lipid and ash did not differ among the different dietary treatments. The protein conversion efficiency (y) was negatively correlated to percentage dietary protein (X) content, the relationship being: y = 62.76–0.62X (r= 0.99; P < 0.01).