Dietary α‐linolenic acid affects lipid metabolism and tissue fatty acid profile and induces apoptosis in intraperitoneal adipose tissue of juvenile grass carp ( Ctenopharyngodon idella)

A 56‐day feeding trial was conducted to elucidate the effects and mechanism action of dietary α‐linolenic acid ( ALA , 18:3n‐3) on lipid accumulation and fatty acid profile of muscle, hepatopancreas and intraperitoneal fat ( IPF ) in juvenile grass carp using three isonitrogenous and isoenergetic semi‐purified diets containing 0.0% (control group), 1.0% and 2.0% ALA , respectively. The lowest intraperitoneal fat ( IPF ) ratio was found in 2.0% group. In the muscle, hepatopancreas and IPF , docosahexaenoic acid ( DHA , 22:6n‐3) and eicosapentaenoic acid ( EPA , 20:5n‐3) contents increased with the increase in dietary ALA . In the IPF , caspase 3, caspase 8 and caspase 9 showed the highest activities in 2.0% group, while the value of Bcl‐2/Bax (B‐cell leukaemia 2/Bcl‐2‐associated X protein) reached the lowest. Meanwhile, swelling of the IPF mitochondria was observed in 2.0% group. The gene expressions of fatty acid desaturase ( FAD ) and fatty acid elongase ( ELO ) in the hepatopancreas and muscle showed significantly higher levels in the treatment groups, whereas an opposite trend was existed in the IPF . Fatty acid synthase ( FAS ), sterol regulatory element binding protein‐1c ( SREBP ‐1c) in the IPF and hepatopancreas reached the lowest in 2.0% group. Overall, dietary ALA could promote n‐3 highly unsaturated fatty acids ( HUFA s) synthesis and suppress the accumulation of lipid by decreasing the expression of related genes and promoting the apoptosis in IPF .