The effects of CRISPR/Cas9 knockout of the myostatin (MSTN) gene and mc4 r gene in channel catfish, Ictalurus punctatus , was investigated. Growth was generally higher in MSTN mutants when compared to controls at all life stages and in both pond and tank environments. Heterozygous F1 mutants were 218% larger than controls at the stocker stage in ponds. Mean expression level of MSTN was 2.90 times higher in controls than in MSTN F1 progeny (p=0.009). Muscle fiber number was 30-40% higher in mutants compared to controls. When challenged with Edwardsiella ictaluri , the causative agent of enteric septicemia of catfish (ESC), MSTN mutants performed equally or better than controls.
Growth was generally higher in MC4R mutants when compared to controls at all life stages and in pond and tank environments. There were no significant differences in body weight between MC4R F1 progeny and controls generated in 2018, although there was a positive relationship between zygosity and growth, with F1 homozygous/bi-allelic mutants reaching market size 30% faster than F1 heterozygotes in earthen ponds (p=0.022) , and another set of F1s growing 37.5% faster to stocker size. Some families grew upwards to 70% faster than control full-siblings with 50% better feed conversion efficiency.
Channel catfish have limited ability to synthesize n-3 fatty acids . MC4R mutants had a 94% increase in eicosapentaenoic acid (EPA, C20:5n-3) and a 21% increase in docosahexaenoic acid (DHA, C22:6n-3) compared to non-edited controls.
MC4R edited channel catfish were sterile, and M C4R appears to have a critical role in regulating the HPG axis. Fertility could be restored by applying a combination of luteinizing hormone releasing hormone analogue and human chorionic gonadoptropin.