Postprandial metabolism of Australian hybrid abalone (Haliotis laevigata x H. rubra) in relation to temperature and dietary protein manipulation

Understanding the physiological responses of abalone to culture conditions and nutritional inputs is paramount to maintain optimal performance under densely stocked farming conditions. High water temperature (>24 C-degrees) is widely accepted as a key contributor to elevated summer mortality. High crude protein levels in modern abalone diets may interact with elevated water temperature to produce detrimental effects on abalone physiological processes but have received scant attention. This study measured the energy used in the digestion, absorption, and assimilation (i.e., specific dynamic action (SDA)) of hybrid abalone (Haliotis laevigata x H. rubra) after four months of acclimation to three protein levels (32, 38 and 44%) at three culture temperatures (12, 17 and 22 C-degrees). Hybrid abalone exhibited significant stepwise increases in meal size as temperature increased from 12 through to 22 C-degrees, contributing to significantly different SDA between the temperature treatments. Resting (standard) aerobic metabolic rate and peak metabolism (peak MO2 ) during SDA both increased with temperature, while SDA duration was lowest at 17 C-degrees. No effect of dietary protein was observed within the temperature treatments for the SDA metrics. Abalone held at 12 C-degrees exhibited significantly higher rates of gonad maturation, particularly among females. When 22 C-degrees-acclimated abalone were exposed to a simulated summer heatwave up to 26(degrees)C, they exhibited similar mortality and metabolic responses across protein treatment groups and there was a trend of steadily decreasing MO2 with sustained 26 C-degrees water temperature, probably due to fasting. These results help to inform best farming practices to ensure optimal diet, growth, metabolic performance, and survival of hybrid abalone in the dynamic farm environment.