Temperature is a major abiotic factor that affects fish digestion and growth and therefore can impact aquaculture production. The optimum temperature for growth for Atlantic salmon (Salmo salar) is around 14°C. However, during Tasmanian summers (the leading location in Australia for Atlantic salmon farming), this species can experience temperatures up to 22°C for several days. These high temperatures result in decreased feed intake, growth and when prolonged, mortality. Some evidence suggests that this reduction in feed intake could be due to limited energy available for aerobic activities such as digestion. With an increase in temperature, the minimum energy expenditure needed for metabolism maintenance increases at a greater rate than the maximum energy the animal is able to produce, thus decreasing the amount of energy available for activities such as growth or digestion. Indeed, digestion is an energetically costly process and can compete for energy allocation with other energetically demanding activities such as swimming, reproduction, and growth. Thus, it is challenging for fish to digest and grow under elevated temperatures. However, digesting and assimilating a meal and its inevitable cost is essential for growth. Hence, fine-tuning diets to provide adequate nutritional requirements and facilitate digestion at elevated temperatures to improve growth in aquaculture salmon is the focus of this study. We aimed to explore the impact of amino acid balance with the supplementation of glutamine – an important amino acid in energy metabolism and gut health - on the cost of digestion and intestine health at elevated temperatures for Tasmanian Atlantic salmon parr. Fish were fed three isoenergetic experimental diets for seven to eleven weeks at 22°C, and growth, energetic expenditure, digestion cost, amino acid plasma variation, and gut antioxidant enzymes were investigated.