CRISPR/Cas9-mediated Acvr1b mutations alter growth performance in grass carp

The transforming growth factor-beta (TGF-beta) signaling pathway is a central regulator of skeletal muscle growth in vertebrates, but the function of Acvr1b (activin receptor type 1B) remains poorly characterized in teleosts. Here, we used CRISPR/Cas9 to disrupt Acvr1b in grass carp ( Ctenopharyngodon idella ) and evaluated growth performance, muscle histology, and myog enic gene expression. Cas9 protein and sgRNAs targeting exons 2 and 3 were co-injected into fertilized eggs, and edited juveniles were identified by T7E1 assay and Sanger sequencing. Acvr1b -edited fish showed significantly improved growth relative to wild-type controls, including a 25.8% increase in body weight and a 7.39% increase in body length. qRT-PCR revealed reduced Acvr1b expression in all examined tissues. Consistent with enhanced muscle growth, mstn was downregulated, myog was upregulated, and myod was unchanged in edited fish. Histological analysis showed increased muscle fiber size and density, indicating that both hypertrophy and hyperplasia contributed to the growth advantage. Together, these findings identify Acvr1b as a promising target for genetic improvement in grass carp aquaculture.