A bacterial disease that had troubled North Carolina’s $14 million-a-year rainbow trout industry for nearly three decades has been reeled in, thanks in large part to a partnership that has changed the way many growers vaccinate their fish.

Skip Thompson, an area specialized aquaculture agent in the N.C. Cooperative Extension Service, and Dr. Jeff Hinshaw, a NC State zoologist based at the Mountain Horticultural Crops Research and Extension Center in Fletcher, have helped farmers manage enteric redmouth (ERM), a disease that causes fish to stop eating and isolate themselves from other fish.

In 1996, ERM was the state’s number one trout disease, causing a 14 to 20 percent loss. The traditional recommendation for protecting trout from ERM was to immerse fingerlings in a solution of antibiotics. However, scientists had found that injecting salmon with vaccine provided better protection than immersion. Hinshaw began experimenting with injection vaccination of North Carolina trout.

“Jeff’s research showed that immersion provided only six months of protection for 80 percent of the fish,” Thompson said. “Injection, on the other hand, protected for the life of the fish, and it protected nearly 100 percent of the fish.”

The next step was to convince industry leaders to adopt the tedious and labor-intensive practice. “Convincing the industry to give shots to five million small fish each year was no easy task,” Hinshaw said.
Thompson started his demonstration efforts with Tellico Trout Farms, an influential grower that operates a large hatchery.

At Tellico growers had the chance to see injected fish side-by-side with un-injected fish. “It became very clear to them that injection works,” Thompson said.

From there, word-of-mouth took over, and, by 2002, about 50 percent of the trout raised in North Carolina were injection vaccinated. Losses to ERM dropped to less than 1 percent, and growers cut their use of antibiotics by 84 percent.

“Enteric redmouth disease has gone from being viewed as something that would wipe out the industry in North Carolina to being viewed as something that’s manageable,” said Tom Ort, manager of Tellico Trout Farms.

Today, North Carolina remains second in trout production, behind only Idaho.

Thompson came to NC State in 1990 after seven years as a fish culturist with the N.C. Wildlife Resources Commission. He received his bachelor’s degree in biology from Rollins College in 1983.

“To me, it’s enjoyable to be able to help people,” Thompson said. “It sounds very corny, but it’s true.”