Effects of dietary grape seed oil and linseed oil on growth, muscle fatty acid composition and expression of putative Δ5 fatty acyl desaturase in abalone Haliotis discus hannai Ino

A 120-day feeding trial was conducted to investigate the effects of dietary increasing levels of grape seed oil (GO) and linseed oil (LO), rich in linoleic acid (LA) and α-linolenic acid (ALA) respectively, on growth, fatty acid composition and expression levels of putative Δ5 fatty acyl desaturases (Fads) in muscle of juvenile abalone (Haliotis discus hannai Ino). Seven experimental diets were formulated to contain increasing amounts (0%, 0.875%, 1.75% and 3.5%) of GO or LO as dietary lipids. Tripalmitin (TP), rich in 16:0, was supplemented to reach 3.5% (dry weight) total lipid. These diets were named as 0%GO/LO (TP), 25%GO, 50%GO, 100%GO, 25%LO, 50%LO and 100%LO. With the increase of dietary GO or LO inclusion, growth parameters (such as specific growth rate of weight) first increased and then decreased (R2 > 0.72, P = 0.000). The survival rate of abalone was not significantly correlated with dietary GO (R2 = 0.04, P = 0.815) or LO inclusion (R2 = 0.50, P = 0.046). The contents of muscle n-6 polyunsaturated fatty acids (PUFA), including LA, 20:2n-6, 20:4n-6, 22:2n-6, were significantly positive correlated with dietary GO inclusion (R2 > 0.895, P = 0.000). A positive relationship was significantly noted between the values of muscle n-3 PUFA (ALA, 20:3n-3, 20:5n-3 and 22:5n-3) and the dietary LO inclusion (R2 > 0.905, P = 0.000). DHA was significantly increased and then decreased with dietary LO increase (R2 = 0.937, P = 0.000). The expression levels of putative Δ5 Fads in 50%GO group were significantly higher than those of other GO groups (P < 0.05). With the increase of dietary LO, expressions of putative Δ5 Fads first increased and thereafter reached a plateau (R2 > 0.929, P = 0.000). These results indicated that biosynthesis of long chain polyunsaturated fatty acid in muscle of abalone could be increased in response to increasing levels of dietary LA or ALA through increased expressions of putative Δ5 Fads. High intakes of dietary LA and/or ALA inhibited the biosynthesis of DHA and compromised the growth performance of abalone.