High growth efficiency occurs over a wide temperature range for juvenile barramundi Lates calcarifer fed a balanced diet

Temperature has a marked and direct effect on many of the key physiological processes in ectotherms, including fish. Results from two growth trials on juvenile barramundi ( 3–5 g) were used to model the effects of temperature on the feed intake and growth performance, measured as specific growth rate (SGR), productive protein value (PPV) and productive energy value (PEV), across temperatures 21–39 °C (at 3 °C intervals). There were no significant differences between the chemical composition of the fish reared at different temperatures. Optimal temperatures were determined from quadratic polynomials: maximum feed intake (g d− 1), maximum growth (SGR, % d− 1) and growth efficiency (PPV and PEV, %) occurred at 32.8, 31.4, 31.2 and 30.2 °C, respectively. These models also determined that maximum growth occurred approximately 4 °C higher then previously demonstrated. Feed intake, SGR and growth efficiency remained ≥ 90% of the maximum biological response over an 8 °C temperature range. These models suggest that juvenile barramundi are eurythermal and therefore maximize growth by adopting strategies to optimize nutrient utilization over as wide a temperature range as possible. Furthermore, the decrease in growth efficiency at extreme (high) temperature occurs over only a few degrees and highlights the upper thermal tolerance of barramundi.