Age-dependent response of digestive enzyme activities to dietary protein level and water temperature in greenlip abalone (Haliotis laevigata)

Proteases, lipases and carbohydrases are digestive enzyme sub-classes that influence the digestive capacity of abalone. In a 12-week study, the effects of age, water temperature and dietary protein levels on digestive enzyme activity in greenlip abalone (Haliotis laevigata) were investigated. One- and 2-year old abalone were fed diets with crude protein (CP) levels from 24 to 36% (18.0-28.6% digestible protein) and cultured at 14, 18 and 22°C. Diets were formulated to be isoenergetic (12.5MJkg^-1 digestible energy) and isolipidic (3.6% crude lipid). Trypsin, α-amylase and lipase activities were measured, and were influenced differently by abalone age, water temperature and dietary protein levels. Lipase and α-amylase activities significantly increased as water temperatures were raised. In contrast, trypsin activity was not affected by water temperature. Trypsin activity of 2-year old abalone was significantly lower (53%) than that of 1-year old abalone. The α-amylase activities of 1-year old abalone were significantly up-regulated as dietary protein levels increased. In contrast, 2-year old abalone down-regulated α-amylase activity by 55% when fed 33% CP, compared to abalone fed 30% CP. The significant trypsin activity down-regulation in 2-year old abalone compared to 1-year old animals provides further support to reducing dietary protein for 2-year old abalone to optimise cultured greenlip abalone production. Significantly higher α-amylase activity in 1-year old abalone as starch levels were reduced indicates a compensatory effect in abalone fed carbohydrate deficient diets. Further research is recommended to optimise the protein to energy ratio for different age classes of greenlip abalone, especially when fed high dietary protein levels.Statement of relevance: Results may contribute to further diet development research.