Virus strikes salmon fry — Hatchery loses sockeye stock to IHN

By Jenny Neyman


Photos courtesy of Cathy Cline, field assistant at the Bear Creek Weir. A Cook Inlet Aquaculture Association crew collects sockeye broodstock for gametes extraction.


Redoubt Reporter

If Trail Lakes Hatchery in Moose Pass were a motel, the sign out front would be proclaiming vacancies. Though the reason why it’s so empty would probably strike prospective lodgers as being a little too like Alfred Hitchcock’s Bates Motel, since the last batch of fish staying there met an untimely demise.

An outbreak of infectious hematopoietic necrosis virus over the summer led to a loss of 1.9 million sockeye salmon fry — the entire stock being reared for release into Resurrection Bay outside Seward, and another 250,000 sockeye fry being reared for release in Tutka Bay in Lower Cook Inlet.

IHN isn’t a new phenomenon, and this outbreak isn’t the worst the hatchery has seen, but it comes at a particularly bad time for the Cook Inlet Aquaculture Association, which operates the state-owned hatchery through contract with the Alaska Department of Fish and Game. At a recent meeting, the CIAA board of directors voted to keep the hatchery open for the time being, but just like the fry, the hatchery itself may soon be facing execution.

“I think everyone is going to wait and see before they put the kibosh on the program. We have basically a year and three-quarters to ponder what we’re going to do, if the program’s going to go forward and in what form,” said Tom Prochazka, Trail Lakes Hatchery manager.


IHN is a deadly viral infection that affects certain types of fish, including sockeye, chinook and chum salmon, and not others, including pink and silver salmon, Prochazka said. When the disease is in an active, clinical stage, it attacks and shuts down the fish’s internal systems. There aren’t many obvious outward physical signs of infection, but the virus does cause a range of aberrant behaviors, such as early hatching, lethargic motion or a lack of swimming, and trailing fecal casts.

While the virus can kill an infected fish, it does not pose a threat to other species. A bear, bird or human could consume the fish and not be harmed, Prochazka said. The concern is with transmission of the virus leading to greater fish mortality. IHN is a waterborne virus, so horizontal transmission — from fish to fish — can occur simply by an infected fish sharing the same water source as other fish. Horizontal transmission can also occur between water sources, through the feces of a predator that eats an infected fish in one lake and carries the infection to another, for example.

The virus also can be transmitted vertically, passed on from parent to progeny. IHN is carried through the gametes, in ovarian fluid in females and sperm in males. Vertical transmission is more rare, but does happen, Prochazka said.

In the wild, the consequences of IHN aren’t as dramatic as in a hatchery setting. Nature has ways of isolating the virus.

“If they’re in a lake or a bigger body of water, typically the sicker fish aren’t going to move with the school. They’re going to be left behind, they’re going to drop out, the other fish are going to get away from them,” Prochazka said. “At a hatchery, for the short term they’re here, from March to May and until we can get them out of the hatchery and plant them in a natural lake, they can’t get away from each other as easily. Whereas, you don’t have that kind of intensity in natural fish pools.”

In hatcheries, regulations mandate that any unit, like an incubator or raceway, found to have an outbreak of IHN must be “rolled.” All the fish in that unit are destroyed and it is sanitized in order to contain the outbreak and prevent infected fish from being released into the wild.

Outbreaks are not an unusual occurrence at Trail Lakes Hatchery, but the scope and timing of this one amplifies its consequences. Typically, IHN is discovered when sockeye eggs are in an incubator. The virus can lay dormant until a stressful event, such as hatching, causes it to become active. IHN can cause early hatching, which tips off hatchery workers to an outbreak.

“Usually, hatching is a stressful event that can cause (IHN to become active) if it’s present. If it’s going to happen, a stressful event like hatching is where, in the past, we’ve usually seen it,” Prochazka said. “We’ve had it multiple times, just about every year we might get one incubator or two that we see IHN. Usually we just kill all the fish, turn off the water and chlorinate it. We have to when we see it. So we haven’t had it spread inside the hatchery. We’ve contained it at that point.”


Grant Sill, fish culturist at Trail Lakes Hatchery, rinses fertilized salmon eggs.


This year, however, IHN didn’t surface until after the eggs hatched and the sockeye fry were ponded in raceways outside the hatchery. They were supposed to be reared there until next spring, when they were to be released to net pens in Resurrection Bay and Tutka Bay. Having IHN show up in raceways is a more rare occurrence, but, again, not unheard of, Prochazka said. He estimated that an IHN outbreak outside of the incubators has hit the hatchery every five to 10 years since it began operation in the early 1980s.

“It can be your fish are in the incubator, they become fry, you pond them and a stressful event can happen there, if it hasn’t already, that can cause the IHN to become clinical,” he said.

In late May there was a spike in mortality in one raceway, where samples tested positive for IHN. Over the next six weeks IHN showed up in the seven other raceways holding sockeye bound for Resurrection Bay and all 1.9 million of those fry were destroyed. IHN also showed up in a raceway holding fry bound for Tutka Bay, and those 250,000 sockeye fry were destroyed, as well.

The outbreak is a disconcerting occurrence, since it suggests that both vertical and horizontal transmission have taken place. The affected fry came from two egg takes, from sockeye stock in Bear Lake and Hidden Lake. Those fish are sampled for IHN every three years. Most recent tests showed an incidence of three in 60 infected with IHN at Hidden Lake. Bear Lake ran much hotter for IHN, at 49 out of 72.

Vertical transmission would result in IHN entering the hatchery as eggs infected by a parent. An outbreak due to vertical transmission is more easily contained at the hatchery because it’s likely to show up while the fish are still in incubators. But it’s also impossible to prevent, short of testing all the brood stock and only taking eggs from uninfected fish, which is an unfeasible endeavor.

Conversely, horizontal transmission of IHN can be prevented, but it’s challenging to do so, especially once fish are in the fry stage and placed outside the hatchery in raceways. Prochazka said that fish are transferred from each incubator into their own raceway, so if one is hit with IHN, just that raceway can be disposed of. Still, IHN is easily transferable, and Prochazka said he wasn’t sure why or how all the fry from all the Bear Lake stock in several different raceways ended up with IHN, plus part of the fry from the stock in Hidden Lake.

“Anything can spread it — we can spread it, birds can spread it, mink can spread it. That’s the bad part about (IHN breaking out in a raceway, versus an incubator). It isn’t because raceways are any less safe than incubators, but because, here, they’re outside and you have more issues to deal with,” Prochazka said.

He said that steps have been taken after previous outbreaks to prevent horizontal transmission of IHN. A fence was installed around the raceways to keep animals away. Bird wires were installed, then bird netting when the wires didn’t prove effective enough. Staff members monitor fish density in the raceways so they aren’t crowed in too close to each other, and caution is taken to ensure water from one raceway doesn’t end up transferred into another.

“As soon as you notice it and get your sample tested then you can get rid of it. Typically we’ve gotten rid of the incubator and haven’t had a further problem. It hasn’t spread from incubator to incubator. But once we ponded those fish and then the IHN has become clinical for whatever reason, then it’s outside and we’ve had more trouble containing it,” he said. “I don’t know if there’s any answers to that. The fact that it spread, I think, is something that we need to work on. I’ve got some ideas and, definitely, the staff and I are going to take a hard look at it.”

At the board meeting, Prochazka offered his hand to be slapped, if the board was inclined to do so.

“I think the buck stops here. I take responsibility for it. It obviously spread. I think it’s incumbent on me to kind of lead the discussion on what can be done to prevent this from happening. I don’t think we can prevent IHN, it’s something that can occur through vertical transmission, and I think this year what happened is the disease didn’t break out until two months after they’d been ponded. Why, I don’t know.”

Ken Tarbox, a retired Fish and Game biologist who represents the Kenai Area Fishermen’s Coalition on the CIAA board, said he didn’t think Prochazka’s offer of responsibility was warranted.

“Disease happens in hatcheries, and sometimes it’s human-caused due to negligence, but in this case we had two brood years, two different stocks, and


Salmon fry in raceways at Trail Lakes Hatchery.


we had both of those stocks hot for IHN. Vertical transmission happens. Things happen. So I think the key here is looking at what’s the risk of this happening again, since we don’t know exactly what the cause of this is. That’s the key point, not that the hatchery manager made a mistake. I don’t think he made a mistake,” Tarbox said.

The board discussed the possibility of installing an ultraviolet, water-treatment system at the hatchery to kill pathogens in the water used for fish rearing. Since the hatchery discharges water into a freshwater system, it is required to treat its effluent before discharge, and has a UV system for that purpose. In the past, it was decided that installing a UV system to treat water influent would be too expensive and would take up too much space, but available technology has shrunk and become more affordable in recent years, Prochazka said.

A previous outbreak of IHN in raceways was attributed to a flood contaminating the well water used for hatchery operations. That problem was addressed by grouting the wells and putting in check valves. Prochazka said he doesn’t think water was the cause of this summer’s outbreak, but he isn’t against installing UV, either, if it may help.

“I don’t think we have water issues, although at one time that was the case. I would be for it,” he said. “I just don’t think it would really change the vectors that much in the hatchery, but it would be another safeguard against. It can take care of any other issues. Like bacteria in the water or pathogens in the water, it can certainly get rid of them.”

The earliest an IHN outbreak shows up in incubators is December, and this outbreak didn’t show until spring, which is far too late to do another egg take to replace the eggs or fry that are lost. The hatchery simply has to wait until next year’s egg take in August and try again. Meanwhile, the fish lost won’t be released into the ocean, won’t return, won’t be caught and won’t bring a financial return to the aquaculture association or fishermen.

The association can withstand a run failure here and there, but this comes at a particularly bad time financially, heaped on top of outstanding loan debt, a need for working capital to honor grant project commitments, the possibility of a net pen failure in Resurrection Bay, and a need for capital if the association is going to switch gears and try something different.

But there’s no scheduling or reasoning with a virus. There’s only attempts to recover and prevent further outbreaks. In this case, it’s a long process to do so.

“You’re looking at four, five years down the road, so you’ve got a lot invested, not only in manpower, labor, expenses, water, feed but then it’s a long journey until you get your results. So when you have to go back to the drawing board, there’s not a quick fix. I can’t fix it for next year,” Prochazka said.

Next week’s story will look at problems with net pens and the association’s financial crisis.



Filed under commercial fishing, ecology, fishing, salmon

7 responses to “Virus strikes salmon fry — Hatchery loses sockeye stock to IHN

  1. Pingback: Tough roe to hoe — Aquaculture association has history of taking on water « The Mouth of The Kenai

  2. Hello
    I want to let you know that there are large and often secret outbreaks of IHN on Atlantic salmon farms along the coast of British Columbia. Our sockeye in the Fraser decline steeply whenever there is an outbreak, please contact me for graphs. BC wild salmon pass these feedlots and then carry on up the coast. If they become carriers they could expose Alaskan stocks to strains of IHN that have reproduced for many generations inside the feedlot environment. We are working hard to get these Norwegian companies disease records to the Cohen Commission, but so far they have refused every government request for data since I began observing outbreaks in salmon feedlots and then in our coho enhancement hatchery (furunculosis). Please contact me if you need more information. The Canadian government has allowed IHN infected farm salmon to remain in the water twice and it has spread to many farms. There are two papers on this.

  3. Kim Neelan

    All farm-raised salmon in BC are vaccinated against the naturally ocurring IHN virus.

  4. Kim Neelan

    Fish health records from BC salmon farms were submitted to the Cohen Commission as requested, contrary to what poster ‘Alex Morton’ says.

    In fact, it is disease records from enhancement hatcheries (all coast including Alaska) that has been requested and denied.

  5. Pingback: Some Good Links | Buchanan Salmon Fishing

  6. Dave Nelson

    All farm-raised salmon are vaccinated against IHN, so that torpedoes that rumour.

  7. Farmed and still dangerous

    Nice try Dave, but either the vaccination is not that effective, or they didn’t vaccinate these fish, which are not the first to show with IHN in BC waters.

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