Towards Season‐Specific Feeds: Maximising Protein Digestibility and Reducing Waste in Hybrid Abalone ( Haliotis rubra × Haliotis laevigata) Aquaculture

ABSTRACT Australian abalone grow‐out aquaculture relies on formulated feeds to provide for the nutritional requirements of the animal. At the same time, grow‐out systems are subject to seasonal water temperature fluctuations. As such, the economic and environmental performance of cultured abalone is inherently tied to the utilisation efficiency of dietary nutrients and changes to water temperature. This study aimed to better understand the effect of water temperature and dietary protein level on nutrient digestibility in Australian hybrid abalone ( Haliotis rubra × Haliotis laevigata ). Hybrid abalone were fed five different levels of dietary protein for 150 days at three distinct water temperatures. Digestibility, nutrient utilisation and calculations of nitrogen assimilation efficiency and undigested nitrogenous waste were assessed. Protein digestibility was negatively affected during both warm (22°C) and cold (12°C) water growing conditions and appeared optimal at 17°C, whereas lipid digestibility increased as the water temperature increased from 12°C to 22°C. An increase in the dietary protein level up to 440 g kg −1 at both 17°C and 22°C improved macronutrient and amino acid digestibility, compared to diets formulated with lower dietary protein. Relationships between water temperature and diet protein level were plotted on response surfaces and showed that maximum protein digestibility occurs at 16.8°C and 46.3% diet protein, whereas maximum dry matter digestibility occurs at 18.9°C and 43.1% diet protein. Taken together, these findings can significantly contribute towards developing season‐specific feeds for Australian hybrid abalone to maximise growth performance while minimising effluent discharge.