Effect of High Water Temperatures on the Utilisation Efficiencies of Energy and Protein by Juvenile Barramundi, Lates calcarifer

This study was undertaken to define the effects of temperature on the energy and protein partial utilisation efficiencies of juvenile Barramundi. The experiment used a factorial design with four temperatures (25oC, 29oC, 32oC, and 36oC) and three ration levels (low, moderate, satiety) to examine the response of Barramundi to varying digestible energy (DE) and digestible protein (DP) intake. Energy and protein deposition with varying intakes at most temperatures were linear, though aberrations occurred at 36oC relative to the other temperatures. The coefficients of DE utilisation were relatively consistent at 0.56 ± 0.02 (mean ± SEM) between 25oC and 32oC, though at 36oC this declined to 0.42 ± 0.04. Similarly the maintenance DE demand for the fish was relatively constant across the range 25oC to 32 oC (~40 kJ DE/metabolic body weight (MBW)/d), but at 36oC dramatically increased to around 110 kJ DE/MBW/d. The coefficients of DP utilisation were also relatively consistent at 0.51 ± 0.02 between 25oC and 32oC, though at 36oC this declined to 0.28 ± 0.12. Similarly, the maintenance DP demand at 36oC dramatically increased from around 0.5 g DP/PBW/d to 1.5 g DP/PBW/d. These results demonstrate that at high temperatures Barramundi protein demand and utilisation is significantly compromised and this affects their ability to efficiently convert dietary protein to tissue growth.