Effects of dietary protein levels on ovarian development in broodstock of Scatophagus argus

Protein is a critical nutrient during fish reproduction, and its intake level directly affects gonadal development and reproductive performance of broodstock. This study evaluated the effects of three dietary crude protein levels-31.21% (Group A), 38.52% (Group B), and 45.80% (Group C)-on ovarian development in broodstock of spotted scat ( Scatophagus argus ). After 8 weeks of feeding, fish in Group B exhibited the highest gonadosomatic index (GSI: 7.74 ± 1.37%), serum estradiol (E2: 229.64 ± 31.88 pg/mL), and vitellogenin (VTG: 1056.66 ± 180.11 μg/mL) levels, which were significantly higher than those in the 31.21% protein group (P < 0.05) but did not differ significantly from those in the 45.80% group. Hepatic total amino acid and essential amino acid contents increased with rising dietary protein levels. Liver transcriptome analysis (Group A vs. Group B) identified 416 differentially expressed genes. qRT-PCR validation confirmed that genes related to sex steroid hormones, ovarian development, and glucose-lipid metabolism such as dgat1, acot1 , cyp7a1 , and kifc3 were significantly upregulated, whereas rgs3 , f stl3 , p rg4 , and socs2 were significantly downregulated. These results indicate that a dietary protein level of 38.52% is beneficial for ovarian development in Scatophagus argus broodstock. Protein nutrition may regulate ovarian development by optimizing glucose-lipid metabolism and feedback regulating the related processes of the hypothalamic-pituitary-gonadal (HPG) axis through liver metabolic pathways.