Effects of dietary grape seed extract, green tea extract, peanut extract and vitamin C supplementation on metabolism and survival of greenlip abalone (Haliotis laevigata Donovan) cultured at high temperature

A major problem confronting the abalone farming industry in Australia is elevated mortality during summer months. Recent research suggests that temperature-induced tissue breakdown allows bacteria entry to the host, and nutritional supplementation can alleviate this breakdown. The aim of this study was to alleviate mortality of greenlip abalone, Haliotis laevigata, cultured at high summer water temperatures (25 °C) by dietary intervention using graded levels of peanut skin extract (PE; 0.5, 1.0, 2.5 and 5%), green tea extract (GTE; 0.5, 1.0, 2.5 and 5%) and vitamin C (1.0% vitamin C; 1.0% vitamin C + 1.0% GTE; and 1.0% vitamin C + 1.0% PE) in a commercial diet; these supplements contain antioxidant and bioactive compounds. The commercial diet containing 5.0% Australian grapeseed extract (GSE) fed at 25 °C was also included as a negative temperature/positive diet control due to improved survival and health of abalone at high temperatures in our previous study. Three-year-old abalone (49.21 g; 70.26 mm) were fed the commercial diet at 22 °C (positive temperature control), and the commercial diet (negative temperature control) and test diets at 25 °C for 38 days. Abalone survival was 85% for the commercial diet at 22 °C, whereas survival of abalone was significantly reduced to 40% when fed the commercial diet at 25 °C. There were no significant differences in survival of abalone fed the commercial diet at 22 °C and those fed 5.0% GSE, 0.5% GTE and 2.5% GTE diets at 25 °C. Supplements did not significantly affect oxygen consumption, ammonia excretion rates and total hemocyte count. Abalone fed 5.0% GTE had significantly lower phagocytic activity than those fed the commercial control diet at 22 °C. Supplementation with PE and vitamin C had no beneficial effects on survival, while GTE holds promise as a potential dietary additive to enhance the survival of abalone at higher water temperature. This study confirms that supplementation of 5.0% GSE in the commercial diet also improves the survival of greenlip abalone cultured at high summer water temperature in the laboratory setting. Statement of relevance Purported to have diverse health benefits including antioxidant, antimicrobial, anti-inflammatory, and anticarcinogenic properties, 5% Australian grape extract, graded levels of green tea extract, peanut skin extract and vitamin C were supplemented in a commercial abalone diet in order to improve survival of greenlip abalone at high water temperature.