Millions of fish are raised in the United States each year, but many die from infection. In theory, genetically engineering fish with genes that protect them from disease could reduce waste and help reduce the environmental impact of aquaculture. A team of scientists has tried to do just that — by inserting the crocodile gene into the genomes of catfish.
Americans go through a lot of catfish. in 2021, Catfish farms in the United States produced 307 million pounds (139 million kilograms) of fish. says Rex Dunham, who is working on genetic improvement of catfish at Auburn University in Alabama.
But catfish farming is also a perfect breeding ground for infections. From the time newly farmed fish hatch to the time they are harvested, around 40 percent of animals worldwide die from various diseases, says Dunham.
Can new gene editing help?
The crocodile gene, which Dunham’s research has found as a possible answer, encodes a protein called cathelicidin. This protein is antimicrobial, Dunham says, and is thought to help protect the crocodiles from getting infections in the wounds they sustained during violent fights with each other. Dunham wondered if animals that had artificially inserted the gene into their genomes might be more resistant to disease.
Dunham and his colleagues also wanted to go one step further and ensure that the resulting transgenic fish could not reproduce. That’s because transgenic animals have the potential to disrupt the ecosystems around them if they escape from farms, out-competing their wild counterparts for food and habitat.
Dunham, Baofeng Su (also at Auburn University) and their colleagues used the gene-editing tool CRISPR to insert the crocodile gene for cathelicidin into the part of the genome that codes for an important reproductive hormone,” Dunham says. Without the hormone, fish are unable to ovulate.
The resulting fish appear to be more resistant to infection. When the researchers put two different types of disease-causing bacteria in water tanks, they found that the genetically modified fish were more likely to survive than their unmodified counterparts. Depending on the infection, “the survival rate of cathelicidin transgenic fish was two to five times higher,” says Dunham.
The transgenic fish are also sterile and can only reproduce if they are injected with reproductive hormones, say the researchers, who publish their results Online on bioRxiv prepress server. The paper has not yet been peer-reviewed.
“When I first [heard about the study], I thought: what on earth? Who would have thought to do this? And why are they? ” Says Greg Lutz at Louisiana State Universitythat was Research into the role of genetics in aquaculture for decades. But Lutz thinks the work is promising—disease resistance can have a significant impact on the amount of waste produced by fish farms, and reducing that waste has been a longtime goal of gene editing in farmed animals, he says.
He says raising disease-resistant fish will require fewer resources and produce less waste overall. Although Lutz is positive about the research, he isn’t convinced that CRISPR catfish represent the future of aquaculture. The gene-editing procedure the team uses is a tricky one, and will probably need to be done for every round of fish hatchery for the hybrid catfish commonly used in fish farming. “It’s very difficult to produce enough of these fish to have a viable, genetically healthy line,” he says.
Ready to eat?
Auburn scientists hope to eventually get approval for catfish genetically modified so that they can be sold and eaten. But this may be a long process.
Only one type of genetically modified fish has been approved in the United States. in 2021, AquAdvantage salmon has finally entered the US market– 26 years after the company behind the fish, AquaBounty first applied for approval from the Food and Drug Administration. The salmon has an extra gene—taken from the genome of another species of salmon—that causes it to grow much larger than it otherwise could.
Suppose the catfish is finally approved for sale. Does anyone eat them? Sue and Dunham think so. Once the fish is cooked, the protein produced by the crocodile gene loses its biological activity, so it is unlikely to have any consequences for the person who eats the fish, Su says. at what rate, Lots of people actually eat crocodile meathe adds. “I would eat it in a heartbeat,” says Dunham.
But Lutz points out that others may not be comfortable with the idea of eating catfish with the crocodile gene. “I’m sure you’ll have people who fully expect a catfish to have a big, long mouth and pointed teeth to bite into,” he says.