Effect of dietary linolenic/linoleic acid ratios on growth performance, ovarian steroidogenesis, plasma sex steroid hormone, and tissue fatty acid accumulation in juvenile common carp, Cyprinus carpio

The present study assessed the effects of different ratios of dietary linolenic acid (LNA) to linoleic acid (LA) from vegetable oils on growth performance, ovarian steroidogenesis, plasma sex steroid hormone, and tissue fatty acids accumulation in juvenile common carp (Cyprinus carpio). With fish oil, peanut oil, and perilla oil as lipid source, five experimental diets containing 32% crude protein and 8% crude lipid were formulated with LNA/LA ratios of 0.97 (control diet), 0.02, 0.46, 1.09, and 1.53, respectively. The diets were assigned to 15 tanks (50 L) of carp, and the fish (8.10 ± 0.11 g, n = 25) were manually fed to apparent satiation twice daily in triplicate groups for 16 weeks. The survival rate and feed conversion ratio were not significantly different among treatments (P > 0.05). Results demonstrated that fish fed diet with LNA/LA ratio of 1.09 exhibited the highest body weight gain, and was no significantly different with fish fed control diet. Fish fed diet with LNA/LA ratio of 1.53 showed the highest gonadosomatic index (P < 0.05). The expression of StAR, 17β-HSD and Cyp19a1a in ovary were up-regulated, and plasma E2 increased with increasing of dietary LNA/LA ratios (P < 0.05). Fish fed diet with LNA/LA ratio of 0.02 showed the lowest plasma E2 and T. The expression of Fads6-a and Elovl5-a in liver expressed higher in fish fed with dietary LNA/LA ratio of 1.09. LNA, LA, Docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA) contents in liver were significantly affected by dietary LNA/LA ratios. LNA content in liver and LNA and ARA content in ovary increased with the increasing of dietary LNA/LA ratios. Results of this study indicated that dietary LNA/LA ratios alter both growth and ovarian development, and provided evidence that balanced LNA/LA ratio was beneficial for growth and ovarian development of juvenile common carp.