These scientists used CRISPR to put an alligator gene into catfish

But catfish farming is also an excellent breeding ground for infections. Between the time farmed fish are newly hatched and the time they are harvested, about 40% of animals worldwide die of various diseases, Dunham says.

Could the new genetic modification help?

The alligator gene, which Dunham’s research revealed as a potential answer, codes for a protein called cathelicidin. The protein is antimicrobial, says Dunham — it’s thought to help protect alligators from developing infections in wounds they sustain during aggressive fights with each other. Dunham wondered if animals that have the gene artificially inserted into their genomes might be more disease resistant.

Dunham and his colleagues also wanted to go further and ensure that the resulting transgenic fish could not reproduce. Indeed, genetically modified animals have the potential to wreak havoc in the wild if they escape from farms, displacing their wild counterparts for food and habitat.

Transgenic survivors

Dunham, Baofeng Su (also at Auburn University) and colleagues used the CRISPR gene-editing tool to insert the alligator gene for cathelicidin into the part of the genome that codes for an important reproductive hormone, “to try to kill two birds with one stone,” says Dunham. Without the hormone, the fish are unable to spawn.

The resulting fish seem to be more resistant to infection. When the researchers put two different types of disease-causing bacteria into tanks of water, they found that the genetically-edited fish were much more likely to survive than their non-gene-edited counterparts. Depending on the infection, “the survival rate of cathelicidin transgenic fish was between two and five times higher,” says Dunham.