Effects of dietary protein level on reproductive performance, transcriptomics and metabolomics of ovaries of female northern snakehead (Channa argus) broodstock

The study investigated the effects of dietary protein levels on reproductive performance, egg quality, and larval health of the northern snakehead (<i>Channa argus</i>) broodstocks. A total of 450 female northern snakeheads (16 months old), averaging 731.49 ± 3.51 g, were randomly distributed into 15 cement pools, with each pool containing 30 fish. Five isolipidic diets comprising 34%, 38%, 42%, 46%, and 50% crude protein (labeled as CAP34, CAP38, CAP42, CAP46, and CAP50) were formulated and fed to experimental fish for 4 months. The results showed that the fertilization rates of northern snakehead broodstock in the CAP42 and CAP46 groups were significantly higher than those in other groups (<i>P</i> = 0.049). The optimal dietary protein levels for northern snakehead broodstock were 41% and 42.2% based on fertilization rate and malformation rate. The plasma vitellogenin (VTG) and estradiol (E2) contents were reduced significantly with the increasing dietary protein levels from 38% to 46% (<i>P</i> < 0.05). Ovarian amino acid (AA) content increased significantly with the increasing dietary protein levels from 34% to 42%, followed by a plateau, while highly unsaturated fatty acid content was significantly higher in the CAP42 group than in the other groups (<i>P</i> < 0.05). Metabolomic and transcriptomic results indirectly indicated that 42% of dietary protein benefited steroid hormone biosynthesis, while 50% of dietary protein facilitated AA metabolism, and 34% of dietary protein enhanced arachidonic acid metabolism. In conclusion, 42% dietary protein is the optimal level for improving gonad development and egg quality in female <i>C</i>. <i>argus</i> by promoting nutrient accumulation and steroid hormone synthesis.