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

Murray cod Maccullochella peelii peelii (Mitchell) is a freshwater Percicht hyid fish considered to have high culture potential. Growth and feed utiliz ation were examined in a 56-day experiment, in which triplicate groups of j uvenile Murray cod (initial weight 21.5 +/- 0.03 g) were fed isocalorific d iets (gross energy content of about 21 kJ g(-1)) containing 40%, 45%, 50%, 55% or 60% protein (designated P40, P45, etc.). Final mean weight, percenta ge 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 pr otein efficiency ratio (PER; 1.98 +/- 0.11) were also best in fish on the P 50 diet, but the differences in these parameters from the corresponding val ues on diets P55 and P60 were not always significant. FCR (Y) was related t o dietary protein content (X), the relationship being a second-order polyno mial, in which Y = 0.004X(2)-0.431X + 12.305 (r = 0.95; P < 0.01). The prop ortions of carcass moisture, protein, lipid and ash did not differ among th e different dietary treatments. The protein conversion efficiency (y) was n egatively correlated to percentage dietary protein (X) content, the relatio nship being: y = 62.76-0.62X (r = 0.99; P < 0.01).