Determining the optimum dietary protein to energy (P:E) ratios in aquaculture species is vital to allow for protein-sparing and faster growth rates, which are highly influenced by temperature, while avoiding the adverse physiological problems associated with high dietary lipids or poor nutrition. A laboratory feeding trial was conducted to investigate the effects of three diets of varied P:E ratios and two different temperatures (18 °C, 22 °C) on the growth, condition, survival and physiology of marron (Cherax cainii Austin and Ryan, 2002). The marron were fed three isonitrogenous diets: LL — Low lipid (6%), ML — moderate lipid (10%) and HL — high lipid (14%), with P:E ratios of 19.1, 17.4 and 16.2 g MJ−1 respectively for 120 days. At the end of the feeding trial, growth of marron increased at 22 °C in all dietary treatments. Marron cultured at 18 °C with LL had a lower Total Haemocyte Count, and there was no effect of temperature or diet on the organosomatic indices, condition or survival rate. Total meat yield was higher at 18 °C than at 22 °C overall. HL at 18 °C resulted in lower growth, lower orbital carapace length increase and a high feed conversion ratio, though there was no effect of dietary lipid content on growth at 22 °C. The temperature had an overarching effect on marron growth, and had a greater influence on marron fed a high lipid diet, where there was a greater difference in weight gain of marron between temperatures with the high lipid diet. The present study concludes that a diet with a P:E ratio of 17.4–19.1 g MJ−1, a lipid level of 6–10% and an energy content of 15–16 MJ kg−1 was optimal for marron under the tested experimental conditions.
