Two feeding experiments were conducted to determine the requirement of young (2-4g) abalone Haliotis discus hannai for essential fatty acids (EFA) by feeding them with diets containing various fatty acids at levels of 1 or 5% lipid for 80 days. Feeding a lipid free or an EFA deficient diet resulted in retarded growth and low feed conversion efficiency (FCE), together with an increased level of sterols in body lipids and ω9 fatty acids in the polar lipid fraction from both viscera and muscle.
Addition of 18:2ω6 and 18:3ω3 or ω3 highly unsaturated fatty acids (ω3 HUFA, a mixture of 20:5ω3 and 22:6ω3) to the diet improved weight gain and FCE. However, the effect of supplementation of 18:2ω6 or 18:3ω3 on growth and FCE was inferior to that of 20:4ω6 or ω3 HUFA. Feeding 18:2ω6 and 18:3ω3 resulted in elevation of 22:4ω6 and 22:5ω3 in the visceral polar lipids, respectively. However, such an elevation was not apparent in 22:5ω6 and 22:6ω3, suggesting a low ability of abalone to convert 22:4ω6 to 22:5ω6 and 22:5ω3 to 22:6ω3, respectiyely.
These results indicate that the abalone requires ω3 and ω6 HUFA as EFA. Judging from the growth rate and EFA index, Σω9/(20:4ω6+20:5ω3+22:6ω3) which was less than 0.8 in the abalone receiving diets with sufficlent amounts of EFA. The requirement of the abalone for ω3 HUFA was estimated to be about 1% of the containing 5% lipid. The requirement was also found to be variable due to dietary lipid level.