Comparative studies on the nutrition of two species of abalone, Haliotis tuberculata L. and Haliotis discus hannai Ino. 5. The role of polyunsaturated fatty acids of macroalgae in abalone nutrition

This study was undertaken to evaluate the nutritional role of polyunsaturated fatty acids (PUFA) in dietary macroalgae for the abalone, Haliotis tuberculata and Haliotis discus hannai. The effects of five species of macroalgae (Alaria esculenta, Laminaria digitata, Laminaria saccharina, Palmaria palmata and Ulva lactuca) on specific growth rates (SGR) of the abalone and, the relationship between abalone SGR and fatty acid profiles in the algae were investigated. The current study confirmed our previous findings. Based on SGR the dietary values of these macroalgae can be listed in a decreasing order as follows: P. palmata, A. esculenta, U. lactuca, L. digitata and L. saccharina for H. tuberculata and, A. esculenta, P. palmata, L. digitata, L. saccharina and U. lactuca for H. discus hannai. Fatty acid analysis revealed thatC18 and C20 PUFA, such as 18:4n-3, 18:3n-3, 20:4n-6 and 20:5n-3, weredominant in the brown algae, A. esculenta, L. digitata and L. saccharina. The red alga, P. palmata, was characterised by the highest proportion of 20:5n-3 among the selected algae. In the greenalga, U. lactuca, however, the dominant PUFA were C16 and C18 fatty acids, while C20 fatty acids were minimal. All the selected algae consistently contained very low levels of C22 fatty acids. Statistical analyses demonstrated that (a) 20:5n-3 played a prominent role in the nutrition of both abalone species (b) 18:3n-3 as well as other n-3 PUFA, and 18:2n-6 together with other n-3,6 long-chained PUFA also contributed to the faster growth of H. tuberculata and H. discus hannai, respectively. The results suggest that the PUFA of both n-3 and n-6 families seem to be essential for growth of H. discus hannai for H. tuberculata, however, growth enhancement appeared to depend largely on n-3 PUFA.