Loss of rbmx function enhances growth and feed conversion efficiency in yellow catfish (Pelteobagrus fulvidraco)

Improving feed conversion efficiency (FCE) is critical for reducing the production costs and faecal waste in the aquaculture sector. However, the mechanisms that regulate FCE remain poorly understood. In this study, phylogenetic tree analysis revealed that the Rbmx protein encoded by the rbmx gene was highly conserved across different species and throughout evolutionary processes. The rbmx mRNA was widely expressed in various tissues of yellow catfish, with the highest expression levels in the liver and gonads. To further investigate the function of rbmx , we successfully established a stable rbmx knockout line in yellow catfish using CRISPR/Cas9 technology. Notably, we found that rbmx knockout significantly enhanced growth and FCE. Specifically, the body weight of rbmx +11 yellow catfish increased by 17.3% and 10.6%, while FCE improved by 20.2% and 17.8%, in males and females, respectively. Transcriptomic analysis further revealed that rbmx deficiency resulted in many differentially expressed genes (DEGs) that were enriched in growth and metabolism pathways. RT-qPCR analysis confirmed the upregulation of key genes involved in growth and metabolism pathways, such as ghra , pparg , and pygl . Taken together, our results demonstrate that rbmx is a negative regulator of growth and FCE in yellow catfish, further providing a theoretical foundation for precision molecular breeding (i.e., genome editing) for improving both growth and FCE in fish.