Growth and feed utilisation of juvenile greenlip abalone (Haliotis laevigata) in response to water temperatures and increasing dietary protein levels

In this 91-day study, the interaction between four dietary crude protein (CP) levels (27, 30, 33 and 36% CP) and three water temperatures (14, 17 and 20°C) on the growth and feed utilisation of 6-month old greenlip abalone (Haliotis laevigata) (0.91g) were investigated. Diets were formulated to be isoenergetic (12.5MJkg^-1 digestible energy), containing a lipid level of ~3.6% and digestible protein from 17.99 to 28.57%. Abalone were fed to excess at 16:00h daily, and uneaten feed was collected the following day. The specific growth rate (SGR) of abalone improved significantly as water temperatures increased from 14 to 17 to 20°C. In addition, apparent protein deposition was significantly higher in abalone at 17 and 20°C compared to abalone at 14°C. There was no significant effect of dietary protein level on SGR, but faster growing abalone at 20°C compensated by consuming more feed when fed low dietary protein levels. In contrast, a significant positive relationship was observed between dietary protein level and feed consumption rate in slower growing abalone at 14 and 17°C. A non-significant tendency for the apparent feed conversion ratio (FCR) to improve was observed in abalone fed high protein diets at 20°C, while at 14°C, abalone had a significantly poorer FCR, especially when fed high dietary protein levels. Based on results from the current study, it is plausible to heat land-based nursery systems in order to gain accelerated growth of juveniles before transfer to grow-out systems. Additionally, no benefits were apparent by feeding abalone high protein diets at 14 or 17°C, and we therefore recommend a dietary protein level of 29% CP at 14 and 17°C. While the SGR of abalone at 20°C was not significantly influenced by dietary protein, the feed consumption rate decreased and there was a tendency for FCR to improve as dietary protein level increased. Therefore, it may be beneficial for abalone to be switched to a diet containing ~35% CP at water temperatures >20°C.