Effect of dietary protein and energy level on growth and body composition of South African abalone, Haliotis midae

The effect of dietary protein and energy level on growth rate, nutritional indices and body composition of two size classes of Haliotis midae was investigated. Diets were formulated to contain three levels of protein (24, 34 and 44%), each with three levels of fat (2, 6, and 10%), to produce diets with estimated protein energy (PE) ratios ranging from 14.5–32.0 mg/kJ. The rates of weight gain, nutritional indices and body composition of both the smaller (0.2-1.0 g) and larger (7.0–14.0 g) abalone were significantly affected by the levels of protein and energy in the diets. Moreover, the two size classes of abalone differed in their responses to the diets. Maximum growth was achieved at a higher dietary protein level in the larger abalone (44%) than the smaller abalone (34%). The protein content of the larger abalone soft tissue was higher (ca. 7%) than the smaller abalone. Irrespective of the lipid content, the percentage of protein deposited by the larger abalone was highest in those fed the 34 and 44% protein diets, whereas that of the smaller abalone was highest for the 24 and 34% protein diets. The condition factor (CF) of small abalone was significantly higher for those fed the 24% protein diets in comparison to those fed the 34 and 44% protein diets, whereas the reverse was found in the larger abalone. It was concluded that the larger abalone had a higher protein requirement than the smaller abalone. Diets containing the highest level of dietary fat (10%) produced significantly lower growth rates and efficiencies of protein deposition in comparison to abalone fed the diets containing 6 and 2% fat, however, these trends were more marked among the small abalone size class. In addition, the feed conversion ratio (FCR) of small abalone fed the 10% fat diets was consistently poorer, but this trend was not present among the larger abalone whose FCR improved with an increasing PE ratio. It was concluded that a dietary lipid level of 10% is too high for H. midae to maintain a maximal growth rate. Proximal analysis of abalone fed the experimental diets revealed that the PE ratio of the diet as well as abalone size significantly affected the carcass composition.