Dietary intervention improves the survival of cultured greenlip abalone (Haliotis laevigata Donovan) at high water temperature

Summer mortality (SM), a disease caused by an interaction between biotic and abiotic environmental factors at high water temperatures (>22°C), impacts health, growth and mortality (up to 50%) of larger (≥60mm) cultured abalone in southern Australia. We aimed to determine if dietary intervention could alleviate mortality demonstrated by abalone at high water temperatures. As this issue is most relevant to farm production, we aimed to demonstrate that different mortality patterns are evident for 2- and 3-year-old greenlip abalone (Haliotis laevigata Donovan), irrespective of reproductive state, and to provide potential, practical solutions to this issue. Growth rate, feed intake and haemolymph variables were measured. To test if dietary intervention could minimise mortality at high water temperatures, we selected a commercial diet routinely fed on-farm when SM occurred, as a negative survival control, and live macroalgae (Ulva lactuca Linnaeus) as a positive survival control. In Experiment 1, 30mm 2-year-old and 70mm 3-year-old abalone were subjected to water temperatures of 18, 22 and 26°C for 36days. In Experiment 2, 60mm 3-year-olds were subjected to 22 and 26°C for 38days. In Experiment 1, survival was >95% for all treatments at 18 and 22°C (P>0.05); whereas, survival was significantly reduced by 35% in 3-year-olds fed the commercial diet at 26°C compared to all other treatments (P