A research priority identified by the Australian Abalone Growers’ Association (AAGA) in 2019, prior to the commencement of the project, was to improve the survival of commercially cultured abalone during periods of high summer water temperatures (> 22°C). This research aimed to address this need. This project was developed by SARDI in collaboration with members of the Australian Abalone Growers’ Association (AAGA), Aquafeeds Pty Ltd and researchers from Flinders University and The University of Adelaide. The primary aim of the project was focused on evaluating the effects of feeding a diet containing 10% dried Ulva sp. meal on improving the survival of Australian Greenlip (Haliotis laevigata) and Tiger Abalone (H. laevigata × H. rubra) cultured throughout summer to autumn in two separate farm trials. Histopathological alterations of selected tissues of the digestive tract and gills of abalone were also assessed for each trial during this period. The secondary aim of the project evaluated the growth, feed utilisation and production cost of abalone for each trial. This project built on research that reported that dietary intervention, utilising dried Ulva sp. meal in a practical commercial formulated feed, reduced mortality in cultured Greenlip Abalone (H. laevigata) associated with elevated summer water temperatures (26°C) under laboratory conditions (Lange et al., 2014).

Abalone in both farm trials experienced mild summers and water temperatures. However, the JTA Avalon trial experienced several instances where water temperatures exceeded 22°C during January and February. The maximum water temperature experienced during the Yumbah Narrawong trial was 22.5°C in early January and remained relatively low compared to those recorded at JTA Avalon. Summer mortality was observed during the farm trial at JTA Avalon, whereas water temperatures were too low during the Yumbah Narrawong trial to induce summer mortality. The dietary inclusion of 10% dried Ulva sp. meal did not result in any significant improvement in survival during either farm trial. In fact, survival appeared to be lower during both farm trials when 10% dried Ulva sp. meal was included in the diets (JTA Avalon survival: commercial diet survival 96.4% vs. 93.4% for the Ulva diet; Yumbah Narrawong survival: commercial diet 98.1% vs 97.5 % for the Ulva diet).
The dietary inclusion of 10% dried Ulva sp. meal did not appear to lead to any significant alteration in digestive tract or gill structure. Heat stress, in combination with commercial culture stressors, appeared to be a factor associated with histopathological alterations observed in abalone during the study, which were chiefly noted in the gill leaflet tips of Tiger Abalone. Gill leaflet tip damage scores appeared to be useful indicators of damage associated with the combination of culture stressors and heat stress in abalone.
In the Yumbah Narrawong trial, which was carried out during mild summer growing conditions, the dietary inclusion of 10% dried Ulva sp. meal improved growth (SGR increased by 9.6% combined with economically irrelevant differences in survival), feed and nutrient utilisation and live biomass yield for a mixed population of Tiger and Greenlip Abalone and compared to the commercial diet ultimately led to a $729 or 8.4% increase in basic sales revenue per slab tank for the 166-d trial period. Unfortunately, due to logistical constraints due to COVID-19, growth performance data were not available from JTA Avalon trial.

Overall, the dietary inclusion of 10% dried Ulva sp. meal did not lead to improvements in survival of Tiger or Greenlip Abalone cultured during summer. Based on the data obtained from the Yumbah Narrawong trial, improvements in growth performance (~9.6% improvement in SGR), feed and nutrient efficiency and basic sales revenue were obtained when abalone were cultured under mild summer growing conditions and fed the Ulva diet compared to the commercial control diet.
Data produced by this project support the concept that diets for improved abalone production should not be formulated on a least cost basis, but rather on an ingredient quality, and abalone and economic performance basis. Feeds formulated on this basis may support improved profitability.