R.J. Van Barneveld, A.E. Fleming, M.E. Vandepeer, J.A. Kruk, P.W. Hone
Abstract:
Previous experiments aimed at defining optimum protein-to-energy ratios in manufactured abalone feed revealed that high energy diets resulted in depressed abalone growth rates. Subsequent investigations showed the higher energy density of the diets was achieved through the addition of fish oil. Given abalone's low requirement for lipids and the small amount of lipase in their gut, it was hypothesized that high levels of dietary lipid depresses the digestibility of other nutrients, such as amino acids, by restricting the action of digestive enzymes. A series of isonitrogenous diets containing 30, 60, or 90 g/kg of either jack mackerel oil or olive oil were formulated and fed to juvenile Haliotis laevigata to determine the apparent fecal digestibilities of dry matter, gross energy, nitrogen (N), and amino acids. Inclusion of jack mackerel oil in manufactured abalone feeds at levels above 60 g/kg decreased the digestion of dietary N and amino acids, and inclusion at levels above 30 g/kg decreased gross energy digestion. Oil type also influenced the apparent fecal digestibility of N, amino acids, and gross energy. Olive oil inclusion had significantly different effects on the digestion of these parameters when compared with jack mackerel oil; however, these differences were minimal up to inclusion levels of 30 g/kg. It was concluded that the addition of marine or vegetable oils to manufactured abalone diets should be limited to 30 g/kg if the digestibility of N, amino acids, and gross energy is not to be affected and that the addition of oils to increase dietary energy levels in abalone diets may not be a cost-effective strategy and may be detrimental to both energy and protein supply.
(Barneveld Nutr Pty Ltd, Lyndoch, SA 5351, Australia)