Effects of dietary protein levels on growth performance, gonadal development, ovarian amino acid composition and reproductive performance in GIFT tilapia (Oreochromis niloticus)

An 8-week feeding trial was conducted to investigate the effects of dietary protein levels on the growth performance, gonadal development, ovarian amino acid composition and reproductive performance of tilapia. Three replicate groups of females (22 fish/tank, 69.05 ± 0.54 g) and male tilapia (8 fish/tank, 81.86 ± 0.94 g) were fed three experimental diets containing 34% (CP34), 39% (CP39), and 44% (CP44) crude protein twice daily to apparent satiation. The results showed that female tilapia exhibited significantly superior growth performance in CP39 and CP44 groups compared to the CP34 group, while male growth performance was improved with increasing dietary protein levels. Meanwhile, the reproductive performance of tilapia was significantly enhanced in CP39 and CP44 groups, as evidenced by significant increases in gonadosomatic index, absolute fecundity, relative fecundity, egg and offspring quality. The analysis of ovarian components showed that the crude protein content was significantly elevated in CP39 and CP44 groups. Meanwhile, analysis of ovarian amino acids profile revealed that multiple essential and non-essential amino acids in the ovaries were significantly accumulated in CP39 and CP44 groups. Histological examination revealed that oocytes in CP39 and CP44 groups exhibited substantial accumulation of yolk granules, whereas a higher incidence of follicular atresia was observed in the CP34 group. Furthermore, dietary protein levels of 39% and 44% may reduce oocyte apoptosis, as evidenced by the downregulated expression of pro-apoptotic genes (including bax , caspase3 , and tp53 ) and the upregulation of the anti-apoptotic gene bcl-2 . In conclusion, optimal dietary protein levels produced beneficial effects on growth performance, gonadal development, ovarian amino acid accumulation and reproductive capacity in tilapia. Based on these findings, maintaining a crude protein level of at least 39% in broodstock feeds for tilapia is recommended. • The appropriate dietary protein levels for tilapia broodstock was determined. • Optimal dietary protein levels benefited for growth and gonad development of tilapia. • Optimal dietary protein levels improved ovarian amino acid accumulation of tilapia. • Optimal dietary protein levels improved reproductive performance of tilapia.