Optimum temperatures for growth and feed conversion in cultured hapuku (Polyprion oxygeneios) — Is there a link to aerobic metabolic scope and final temperature preference?

• Optimal temps for growth/FCR in P. oxygeneios, a novel NZ culture species
• The utility of AMS/Tpref as tools for determining the optimal temp for growth/FCR
• The link between AMS/Tpref and growth/FCR in a novel culture species

As temperature-based growth trials are lengthy, expensive and laborious to run, juvenile hapuku (Polyprion oxygeneios) were employed to assess whether respirometric tests and behavioural preference methods could be used to resolve the optimum temperature for growth and feed conversion efficiency in novel culture species. On the basis that the energetic costs of rapid growth are substantial and need to be accommodated physiologically, it was hypothesised that maximal growth and optimal feed conversion (feed conversion ratio, FCR) would be maximised at temperatures where aerobic metabolic scope (AMS) was also maximised. It was further hypothesised that hapuku would behaviourally self-select temperatures that lead to the greatest level of AMS, growth and FCR performance. Acclimating hapuku juveniles to 12, 15, 18, 21 and 24 °C for 4 weeks resulted in a peak in specific growth rate (SGR) at 18 and 21 °C with slower growth at lower and higher temperatures. AMS was also maximal between 18 and 21 °C and was therefore tightly linked with SGR. The behavioural thermal preference (Tpref) range of hapuku also fell within the optimum range for growth. FCR, however, was inversely related to temperature with the most and least efficient rates of conversion occurring at 12 °C and 24 °C respectively. Though AMS and Tpref had no utility in predicting the optimal range for FCR, standard metabolic rate (SMR) showed a positive linear relationship to FCR. The conclusions of the study are threefold: 1) Hapuku select temperatures that optimise both AMS and growth. 2) AMS and Tpref appear tightly linked with SGR and could possibly be used to predict the optimum temperature for growth in novel species. 3) AMS and Tpref have no utility in predicting the optimum temperature for FCR.