New Brunswick·Science

New Brunswick scientists seek cod parasite vaccine

New research into a parasite that damages Atlantic cod is aimed at preventing infection and could help repair an industry plagued by problems in recent years.

Researchers look to prevent infection, help troubled aquaculture industry

New research into a parasite that damages Atlantic cod is aimed at preventing infection and could help repair an industry plagued by problems in recent years.

Loma morhua is an infectious parasite that latches onto the gills of the large fish, draining them of health. It is partly to blame for the cod aquaculture crash a few years ago in Atlantic Canada.

Researchers say that the parasite might be causing the fish to slowly drown, or become dehydrated.

“Given the fact that the parasite establishes on the gills of the fish — that ultimately it causes an impermeability for fish to acquire oxygen in the water,” says Michael Duffy, head of the research team at the University of New Brunswick.

“If fish can't breathe, it will cause them issues.”

Another theory is the infection may cause fish to have problems with salt exchange.

“This would lead to the actual dehydration of the fish,” said Duffy, who is an associate professor of biology. “Surprising, given the fact that they live immersed in water.”

Loma jumps quickly from fish to fish and it doesn't take long for large schools to become completely infected. Aquaculture pens are especially vulnerable, as hundreds of fish are so close together.

“It not only causes mortality in fish,” says researcher Aaron Frenette, “but fish that survive infection have declining health.”

A fish infected with Loma tends to lose body mass, which translates into poor yields for the aquaculture industry.

Vaccination trials

Frenette's first step in his research was to map out the parasite's life cycle.

“It hadn't been done,” Frenette said. “So figuring out the basics now lets us figure out a vaccine or some kind of treatment.”

Vaccination trials funded by Natural Sciences and Engineering Research Council of Canada are set to start in the next couple of weeks, but cod are challenging. Unlike most vertebrate animals, cod don't produce antibodies.

It gave us a really good feel for how frustrating it was for industry to deal with this parasite- Michael Duffy, associate professor of biology at the University of New Brunswick

“It's a bit surprising and unique,” Duffy said. “But we do feel that they have some immune capacity to deal with pathogens, or they wouldn't be able to survive.”

“We're trying a very crude vaccine to see if, in fact, we can protect some fish, give them some protection,” Duffy said. “We're going to take killed parasites and we will inject them into the fish.”

Using dead viruses and infections is a technique often used to build up an immunity in a body.

Just getting to this stage in the project has been a nightmare. Loma is so infectious that it took the team almost four years to acquire an infection-free population of fish to study.

“It gave us a really good feel for how frustrating it was for industry to deal with this parasite,” Duffy said.

Frustrating and costly.

“There was a hatchery we used to work with in New Hampshire that actually lost an entire production unit, they lost a million cod associated with the parasite just inadvertently gaining access to the fish,” he said.

“This whole process is being used as a template. The fish species in the ocean are being depleted over time and so there will be more and more pressure to produce these various species of fish in aquaculture and treat the infections that will arise.”