Reproductive performance of female largemouth bass (Micropterus salmoides) broodstock was enhanced by dietary small peptides

To research the effects of dietary small peptides on the reproductive performance of largemouth bass ( Micropterus salmoides ) broodstock, four isonitrogenous and isolipidic diets were prepared by adding 5 % small peptide (SP) on two fish meal levels (40 and 20 %), which were labeled as HF (40 % FM), HS (40 % FM+5 % SP), LF (20 % FM) and LS (20 % FM+5 % SP), respectively. 160 female largemouth bass broodstock (initial body weight: 452.36 ± 15.54 g) were randomly allocated to four groups with 4 tanks per group of 10 fish each. A 30-day feed experiment was conducted. Results showed that gonadosomatic index (GSI) of largemouth bass was higher in the 5 % SP group (8.51 ± 1.57 %) than that in the 0 % SP group (7.74 ± 1.82 %) ( P < 0.05); GSI (6.83 ± 0.95 %) and relative fertility (RF, 90.64 ± 15.68 eggs/g) were significantly lower in the 20 % FM groups ( P < 0.05), based on two-way ANOVA analysis. The contents of vitellogenin (VTG, 318.15 ± 26.15 μg/L), estradiol (E2, 42.90 ± 0.31 ng/L) and follicle-stimulating hormone (FSH, 23.04 ± 0.74 U/L) in serum were higher in the HS group than those in other groups ( P < 0.05). The mRNA expression levels of vitellogenin receptor ( vgr , 1.64 ± 0.41), follicle stimulating hormone receptor ( fshr , 1.77 ± 0.35) and cytochrome P450 17a ( cyp17a , 2.42 ± 1.02) in gonad were up-regulated in the 5 % SP group ( P < 0.05). The mRNA expression levels of vgr (1.90 ± 0.29), insulin-like growth factor-1 (1.53 ± 0.67), steroidogenic acute regulatory protein (2.59 ± 0.78), fshr (1.97 ± 0.35) and cyp17a (2.78 ± 1.32) in gonad were up-regulated in the HS group ( P < 0.05). The results indicated that the reproductive performance of female largemouth bass could be enhanced by adding 5 % SP to 40 % fish meal die. However, reproductive performance was negatively affected by 20 % fish meal in the diet, which provided a reference for the application of small peptides in the formulated feed for largemouth bass broodstock. • Low fish meal (20 %) had a negative effect on the reproductive performance of female largemouth bass. • Dietary 5 % small peptides can promote the biosynthesis of VTG, increase the GSI of female broodstock. • Dietary 40 % fish meal added 5 % small peptides improves the reproductive performance of female broodstock.