Larger Fish Fillets Connected to Gut Microbiome

Grad student transplants gut bacteria to increase aquaculture yields

Image Credit: Guglielmo Raymo at the aquaculture facility where rainbow trout are raised for various research projects.

September 8, 2023 Kimbra Cutlip

With the global population on the rise and new agricultural land in short supply, aquaculture offers untapped potential to increase global food production and help feed the world.

PhD student Guglielmo Raymo is researching ways to make aquaculture even more productive by manipulating the bacteria in the digestive tracts of fish. He aimed to build off of research from his advisor, Associate Professor Mohamed Salem in the Department of Animal and Avian Sciences, who previously showed that rainbow trout from families with larger muscles had a different collection of bacteria in their guts than rainbow trout from families with smaller muscles.

Scientists believe that certain gut bacteria may be more efficient at converting food to energy, which helps fish pack on muscle mass—and that translates to larger edible fillets. Given this, Raymo wanted to find out if he could boost the size of small fillet-producing fish  by colonizing their digestive tracts with the same microbiome as the bigger-fillet-producing fish.

It turns out he could. Not only did the gut bacteria recipients pack on the weight, but Raymo documented changes in molecular processes related to their metabolism, like their cellular response to insulin and their muscles’ ability to take up oxygen.

“In the long-term, the goal would be to develop feed formulations, probiotics or prebiotics, and even water supplements that could increase the fishes’ efficiency at putting on muscle mass,” Raymo explained. “But right now, we’re just trying to understand what’s happening at the molecular level to cause these changes.”

Similar questions are being asked by researchers who study mice, pigs, and even humans, where the role of the gut microbiome in diabetes and obesity is a hot topic. But very little is known about the gut microbiome in fish and the role it plays in fish metabolism and health.

To conduct his study, Raymo raised rainbow trout eggs in a sterile environment and dosed them with antibiotics to prevent bacteria from growing in the guts of the developing fish. He used eggs with a low-yield genetic profile, meaning they came from a family that generally produced small fillets.

When the eggs hatched, and the fry began to eat, Raymo divided them into two groups of 30 fish each. He gave half of them feed spiced with gut bacteria from high-yield fish, and the other half got feed mixed with gut bacteria from low-yield fish.

Five months after hatching, the fish fed on high-yield gut bacteria put on 25% more muscle weight than the other group. Unfortunately, during the course of the study, more fish died in the high-yield group than the low-yield group. Raymo can’t say if that was caused by the microbiome treatment or some other artifact of the experiment itself. For that, he’ll need to repeat his experiment, scaling up the number of fish in the study and including a control group that receives no bacteria-spiced feed.

Fortunately, for Raymo, it’s an experiment with endless potential in a virtually unexplored field that puts him at the leading edge of aquaculture advancements.

“I think there are several career’s worth of questions just in the gut microbiome of fish,” Raymo said. “I can see myself continuing to study this topic for a long time."