Effects of Dietary Protein Sources on the Ovarian Development of Female Largemouth Bass (Micropterus salmoides) Broodstock

To investigate the effects of three protein sources—Hermetia illucens larvae meal (HIM), Chlorella meal (CM), and Stickwater meal (SWM)—on ovarian development in largemouth bass broodstock, these protein sources were used to replace 0% (control group FM, containing 40% fishmeal), 25%, and 50% of the fishmeal in the diet. A total of seven isonitrogenous and isolipidic diets were formulated (FM, 25% HIM, 50% HIM, 25% CM, 50% CM, 25% SWM, and 50% SWM). Healthy female fish with an initial body weight of 353.57 ± 28.12 g were fed these diets for eight weeks. The results showed that the viscerosomatic index, gonadosomatic index, and egg diameter of broodstock in the 50% HIM group were significantly higher than those in the FM group. The relative fecundity of broodstock in the 50% HIM and 25% CM groups was significantly higher than in other groups. The relative mRNA expression of hepatic vitellogenin (Vg) was significantly upregulated in the 50% HIM group, while the relative mRNA expression of Vg and vitellogenin receptor (VgR) in the ovary was significantly upregulated in the 25% SWM and 50% SWM groups. In conclusion, replacing 50% of the fishmeal in the diet with Hermetia illucens larvae meal can enhance ovarian development in largemouth bass broodstock by increasing the gonadosomatic index, and relative fecundity, and upregulating the expression of genes related to vitellogenin synthesis (Vg).