But what special abilities do these super fish possess?
This is an American catfish (Ictalurus punctatus), a type of catfish related to the catfish and pangasius found in Vietnam. Its exterior resembles that of a typical catfish, with a smooth, scaleless body and a protruding mouth adorned with whiskers.
However, don’t be deceived by appearances. Within the genetic makeup of this catfish lies a gene from a crocodile. Scientists have used CRISPR, the most advanced gene-editing technology available today, to inject genes from the Chinese alligator (Alligator sinensis) into this American catfish.
The question arises: What was their purpose in doing this?
This is an American catfish (Ictalurus punctatus) carrying crocodile genes.
In fact, scientists did not intend to create a school of catfish with sharp teeth or the hunting skills of crocodiles, which could terrify any American during outings by rivers, lakes, or open waters.
According to a recent study published on the peer-reviewed scientific platform bioRxiv, these catfish were injected with crocodile genes to enhance their resistance to disease.
Four out of ten catfish are born to die from infection
The United States is known for its high fish consumption, especially catfish species like pangasius, basa, and channel catfish. In 2021, statistics showed that farms in the U.S. produced up to 139 million kg of catfish while still needing to import fish from other countries.
“On average by weight, up to 60-70% of aquaculture activities in the United States are aimed at producing catfish“, said Dr. Rex Dunham, an animal geneticist at Auburn University, Alabama.
“Millions of catfish are raised in the United States each year, but among them, millions will die from diseases, mainly infections.
Catfish dying en masse.
Scientists estimate that only 60% of catfish eggs can survive and mature until they are large enough for harvest. This means that 40% of the remaining fish will die at some point before reaching maturity.
Catfish often die from infections, as the wet conditions of fish farms are conducive to the proliferation of many disease-causing bacteria. And when fish are raised in high-density conditions, they easily transmit pathogens to one another.
A dead fish floating on the surface of the pond means all the other catfish below are in danger.
To mitigate this, many farm owners have resorted to mixing high concentrations of antibiotics into fish feed. However, this can leave drug residues on the products and promote the development of antibiotic-resistant bacteria.
Many farm owners have resorted to mixing high concentrations of antibiotics into fish feed.
Therefore, a group of scientists at Auburn University thought: Why not genetically modify catfish to make them resistant to diseases?
But how?
The logic was to find an extremely healthy freshwater fish and transfer their genes to the weaker catfish. So what fish could be more suitable than a crocodile!
Injecting crocodile genes into catfish, but preventing them from spawning
“Theoretically, genetically modifying catfish with genes that protect them from diseases could reduce waste and help mitigate the environmental impact of fish farming. We have attempted to do this – by introducing crocodile genes into the genome of a catfish species, in this case, the American catfish“, Dr. Dunham explained.
The crocodile gene that Dr. Dunham used was obtained from the Chinese alligator, encoding a special protein known as cathelicidin. Dr. Dunham stated that this protein has antibacterial properties—it is believed to help protect crocodiles from infections after they bite each other and sustain injuries.
Thus, he and his colleagues tested whether this gene could be inserted into catfish to see if they could resist infections caused by bacteria.
The cathelicidin gene has antibacterial properties helping to protect crocodiles from infections in their fierce battles with each other.
However, for this experiment to be approved, Dr. Dunham and his colleagues had to meet a condition from the U.S. Department of Agriculture. That is, the genetically modified catfish would not be allowed to spawn.
Indeed, they are not permitted to reproduce. U.S. Department of Agriculture officials are concerned that if scientists create a mutant species of catfish, they could become super fish once released into the wild.
These super fish could cause a disaster due to their competitive advantage over other fish species. They would multiply in enormous numbers that no species, including humans, could control.
To prevent this from happening, Dr. Dunham consulted with Associate Professor Baofeng Su, also a genetic researcher at Auburn University. Baofeng proposed using CRISPR editing tools to transfer the cathelicidin gene from the Chinese alligator to the section of the genome that encodes a crucial reproductive hormone in American catfish.
What would happen if crocodile genes were transferred to catfish?
This would effectively silence the gene encoding the hormone. “We are trying to kill two birds with one stone. Without the hormone, the catfish will not be able to reproduce“, Dr. Dunham said.
What kind of madness is this?
Dr. Greg Lutz, a geneticist from Louisiana State University, remarked that when he first heard about the idea from the Auburn scientists, he exclaimed, “What kind of madness is this? Who could think of injecting crocodile genes into catfish?“
Dr. Lutz himself has many years of experience in the aquaculture industry. However, after reading the article on bioRxiv, he understood why the Auburn scientists pursued this approach.
According to Dr. Dunham’s group report, after receiving the cathelicidin gene from the Chinese alligator, the American catfish indeed developed a higher resistance to diseases.
When scientists released these catfish into a tank containing two pathogens known to infect and kill catfish, the survival rate of the genetically modified catfish increased fivefold compared to non-modified fish.
The survival rate of genetically modified catfish increased fivefold compared to non-modified fish.
Dr. Dunham stated that this gene-modified fish is also sterile, as the gene producing their hormones has been silenced. This ensures they can only survive one generation, even if they escape from the laboratory’s confinement.
Commenting on these results, Dr. Lutz believes that genetically modified catfish have promising potential for application.
“For a long time, creating fish species with high disease resistance has been one of the goals of the aquaculture industry. Gene editing to achieve this aim will significantly impact the waste produced by fish farms“, he said.
“Theoretically, breeding disease-resistant fish would require fewer resources and produce less waste.”
Is genetically modified fish safe to eat?
That is clearly the ultimate goal of this research. Scientists have created a catfish species carrying the disease-resistant genes of crocodiles, solely to increase their farming yield for human meals.
However, for a genetically modified catfish to be approved as food in the U.S., it could be a long journey.
Currently, only one type of genetically modified fish has been approved by the U.S. Food and Drug Administration (FDA), which is the AquAdvantage salmon. These fish have been supplemented with a gene from another salmon species, allowing them to grow larger and produce more meat than regular salmon.
Genetically modified super salmon.
AquAdvantage salmon was approved for the U.S. market in 2021. However, this was the result of 26 years of applications and continuous safety demonstrations by AquaBounty, the company that genetically modified these fish.
But assuming the catfish and catfish species injected with crocodile genes are approved for sale, the question remains: Would anyone actually eat them?
Dr. Dunham believes there is a possibility. Once the fish is cooked, the protein produced by the genes from the alligator will lose its biological activity. Therefore, it poses no risk to those who consume the fish.
“Anyway, many people are still eating alligator fish,” Dr. Dunham stated. “I would be willing to eat these fish right away,” Dunham said.
However, Dr. Lutz expressed concern that others might be uncomfortable with the idea of eating a catfish with alligator genes. “I can assure you that there will be people who fear this fish might grow a large jaw and a long mouth like an alligator to bite back at humans, let alone the thought of eating them,” he remarked.
Nonetheless, since the genes transferred from the Chinese alligator do not encode for the phenotype of catfish, it’s merely a rather interesting imagination.
