CRISPR/Cas9-mediated mstnb knockout enhances muscle growth in salt-tolerant tilapia

Growth is a critical trait in aquaculture, directly affecting productivity and economic value, and targeted genetic manipulation has the potential to enhance growth performance. In this study, we generated a homozygous mstnb knockout salt-tolerant Mozambique tilapia using CRISPR/Cas9. We also evaluated growth, morphology, histological characteristics, selected gene transcripts, and muscle fatty-acid composition under freshwater and seawater conditions. mstnb?/? fish exhibited markedly enhanced growth, observed together with muscle fiber hypertrophy and increased body cross-sectional dimensions. Reproductive traits, including gonadal histology, sex-related gene expression (dmrt1 and amh), and fertility in freshwater, appeared largely unaffected. In the liver, histological vacuolation was observed alongside reduced nrf2 mRNA expression, with no change in sod2. Muscle fatty acid profiling revealed elevated n-3 polyunsaturated fatty acids (DHA and EPA) and an increased omega-3/omega-6 ratio. These findings indicate that mstnb disruption promotes muscle growth, with limited evidence of reproductive effects in freshwater. The results highlight the potential relevance of this approach for aquaculture production, pending further validation under commercial conditions.