Effect of dietary lipid level on growth and feed utilization in cultured South African abalone Haliotis midae L. fed diets with a constant protein-to-energy ratio

The aim was to test whether abalone growth and feed conversion ratio (FCR) could be maintained at increased dietary lipid levels if the protein: energy ratio (P: E) was kept constant. Two size classes (25-30 and 65-70 mm) of Haliotis midae were fed diets with graded levels of lipid (4-16%), in which total protein varied (34-39%) to maintain a constant P: E (22 g protein MJ(-1)). For both size classes, overall performance was best on diets containing 4% and 7% lipid. Above 7% lipid, specific growth rate, shell length increment and protein efficiency ratio decreased while feed consumption and FCR increased significantly. The observed deterioration in growth and nutritional performance in diets with > 7% dietary lipid was more marked in the 65-70 mm size class than in the 25-30 mm class, indicating that the smaller size class were better equipped to metabolize higher levels of dietary lipid. We concluded that the observed decrease in growth and feed utlization with the increasing dietary lipid was not due to an imbalance of dietary protein relative to energy, but rather that H. midae is unable to effectively utilize lipids as an energy source at levels in excess of 7% due to inherent physiological constraints.