Optimal dietary protein level for juvenile southern rock lobster, Jasus edwardsii, at two lipid levels

This study determined the effect on growth efficiency, nutrient retention and apparent digestibility of varying dietary protein concentration and protein/energy ratio for juvenile southern rock lobster, Jasus edwardsii. Isoenergetic diets were formulated at six crude protein levels (5% increments between 24% and 50%) and at each of two lipid levels (5% and 9%). Duplicate groups of 10 lobsters (initial weight mean 3.58 SE 0.86 g) were held in 50-l tanks, in a recirculating seawater system at 18 degrees Celsius and fed to 95% satiation over a 12-week growth trial. There were significant ( P < 0.05) differences in apparent crude protein digestibility (76.4-83.2%), but no difference in dry matter (mean 59.1 SE 0.8%) or energy digestibility (mean 77.7 SE 0.8%). Survival, feed intake, digestive gland index, protein efficiency ratio, energy efficiency ratio and whole-body composition were not significantly affected by dietary treatment. The relationship between nutrient intake and weight gain indicated optimal dietary digestible crude protein (DCP) levels of 29% and 31% when lobsters were fed diets containing 5% and 9% lipid, respectively. For the two lipid levels studied, the optimal dietary protein/energy requirement was similar for maximum weight gain (29 gDCP/ MJ DE) and feed conversion ratio (FCR, 30 gDCP/MJ DE)