Effects of different lipid sources on ovarian maturation in female broodstock of largemouth bass (Micropterus salmoides)

To explore the optimal dietary lipid source for female broodstock of largemouth bass (Micropterus salmoides), this study investigated the effects of fish oil (FO), soybean oil (SO), rapeseed oil (RO), coconut oil (CO), and a 1:1 FO+ SO diet (MO) on liver health and ovarian development. A total of 150 largemouth bass broodstocks (initial body weight: 410.69 ± 6.97 g) were randomly assigned to five experimental groups (3 replicates per group, 10 fish per replicate) and fed the corresponding experimental diets for 5 weeks. The results demonstrated that 1) Serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities in RO and CO groups were significantly higher than those in the other treatment groups (P < 0.05); 2) Compared with the MO group, the FO group showed significantly decreased activities of total antioxidant capacity (T-AOC), total superoxide dismutase (T-SOD), acid phosphatase (ACP) and alkaline phosphatase (AKP) in the liver (P < 0.05); 3) Hepatic histopathological analysis revealed the presence of nuclear dissolution and vacuolar degeneration were present in the SO, RO, and CO groups; 4) The gonadosomatic index (GSI) values of the SO and MO groups were significantly higher than those of the RO, CO, and FO groups (P < 0.05). Meanwhile, oocytes in the SO and MO groups were predominantly at stages IV and V, whereas those in the RO and CO groups were mostly at stages II and III. Notably, feeding sole vegetable oil-based diets led to a considerable proportion of atretic follicles in female broodstock; 5) Furthermore, MO group exhibited the highest mRNA expression levels of reproduction-related genes, including 17β-hydroxysteroid dehydrogenase (17β-hsd), vitellogenin (vg), vitellogenin receptor (vgr) and luteinizing hormone receptor (lhr). Collectively, supplementing diet of largemouth bass broodstock with a 1:1 FO + SO blend as the lipid source effectively promoted ovarian maturation and enhanced hepatic function.