CRISPR/Cas-9 induced knockout of myostatin gene improves growth and disease resistance in channel catfish (Ictalurus punctatus)

Channel catfish, Ictalurus punctatus, is the most produced aquaculture species in the United States, although production levels have decreased since their peak in 2003. Myostatin (mstn) regulates skeletal muscle growth and has been identified as an important gene for increasing body weight in aquaculture species. In this study, the effects of CRISPR/Cas9 knockout of the mstn gene in channel catfish were investigated. Three sgRNAs targeting exon 1 of the channel catfish myostatin gene were microinjected with Cas9 protein in embryos. A total of 209 fish survived to 6 mph after microinjection of Cas9 and sgRNA targeting exon 1 of the mstn gene over the 3 yr experiment (2017-2019) with an average mutation rate of 58%. Successful generation of myostatin knockout (MSTN KO) F1 heterozygotes was achieved in 2019 by individually mating two pairs of control females with MSTN homozygous KO males. The offspring of both families inherited the mutation at a mean rate of 88%. Growth was generally higher in MSTN mutants than controls at all life stages and environments. P1 MSTN mutants were 88% larger than controls at the stocker stage (100 to 200 g) and 27% larger than controls at market size. Heterozygous F1 mutants were 218% larger than controls at the stocker stage. MSTN mutants had reduced overall expression levels of mstn compared to controls. When challenged with Edwardsiella ictaluri, the causative agent of enteric septicemia of catfish, MSTN mutants performed equally or better than controls. With a high mutation rate and inheritance as well as improved growth and disease resistance, using MSTN gene-edited channel catfish could greatly benefit commercial farms.