Comparative Transcriptomic and Metabolomic Analysis Reveals the Regulatory Mechanism of Feed Conversion Efficiency in Spotted Knifejaw (Oplegnathus punctatus)

The spotted knifejaw (Oplegnathus punctatus) is an economically valuable marine fish in aquaculture in China. However, the feed cost has become a bottleneck constraining the commercial benefit. Improving the feed conversion efficiency (FCE) is one of the key pathways to reduce the feed cost, yet the regulatory mechanisms underlying the FCE trait remain unclear. Here, we measured the FCE and conducted comparative transcriptomic and metabolomic analyses between fish groups with high and low FCE. Through transcriptomic profiling of muscle tissues, we identified 297 differentially expressed genes (DEGs), which are significantly enriched in extracellular matrix (ECM) organization and circadian rhythm pathway, indicating that these pathways may play important roles in the regulation of FCE. The downregulation of the ECM genes (e.g., col11a1, dcn, matn2, spon2 and mmp14) indicated the synthesis process of ECM might be attenuated through transcriptional regulation. Upregulation of acly and sds gene transcription points to optimized metabolic efficiency, securing energy for protein deposition. The metabolomic analysis identified 80 differential metabolites (DMs) such as proline (Pro), histidine (His), valine (Val),etc. These DMs were significantly enriched in aminoacyl-tRNA biosynthesis, which implies the high feed conversion efficiency (HFCE) group has a potential increase in free amino acids and protein synthesis. Integrated analysis revealed that protein turnover and amino acid metabolism were significantly enriched at both omics levels. In addition, glutaminase 2 (gls2) gene and succinate were identified as the key regulatory nodes, which may influence the allocation of amino acid substrates to the tricarboxylic acid (TCA) cycle by inhibiting glutaminolysis. These preliminary results provide exploratory insights into the regulatory mechanisms underlying FCE and lay an initial theoretical foundation for artificial selective breeding of HFCE spotted knifejaw.