infectious hematopoietic necrosis

IHN, also known as IHNV, AKA "sockeye disease" AKA "Sacramento River Chinook Disease" is a virus that infects wild salmon, and can wipe out a hatchery stock of trout or salmon within a week. (It’s usually wild fish that infect farmed fish, and not the other way around).

First described in the 1950’s, known susceptible host species are: rainbow or steelhead trout (Oncorhynchus mykiss), Pacific salmon including sockeye salmon (O. nerka), chinook salmon (O. tshawytscha), chum salmon (O. keta), yamame salmon (O. masou), amago salmon (O. rhodurus) and coho salmon (O. kisutch), and, thanks to the exportation/importation of infected specimens to Europe, Atlantic salmon (Salmo salar).

Naturally, the fishing industry is interested in funding research on this virus. Current focus is on developing a DNA vaccine.

Why would I suspect IHVN?
You should always suspect it. Look for these signs in your salmonids:

• long, opaque, off-white fecal casts tailing from the anus of the fry;
• a rosy glow, due to hemorrhaging under the skin;
• protruding eyes (exopthalmia);
• swollen abdomens;
• lethargy;
• darkening of skin color;
• hemorrhaging at the base of the fins.

But, in order to rule out infectious salmon anemia, you’re going to have to do a cell culture to be sure. I’d write up the instructions here, but there’s a more helpful version at OIZ. (See sources, below).

Will antibiotics save my fish?
No. It’s a virus. There’s no way to save your fish.
If your salmon or trout do have IHNV, you’re going to have to turn your fish into fish meal.

1. Transport it in a closed system to a rendering plant and make sure they lightly bake the meal (Fifteen minutes at 60 degrees Celsius ought to kill off the virus).
2. Meanwhile, you’ll have to disinfect the transportation water. (You can’t dump infected water. Treat it with chlorine.
3. Of course, you can’t dump chlorinated water back into the ecosystem, so you’ll have to de-chlorinate the water (try sodium thiosulfate).
4. Oh, and you won’t be able to use your fish farm for 3 months.

Is this virus really as nasty as you've made it sound?
Hey, I don't make this stuff up. The virus is in the same order (Mononegavirales) as Ebola. This fact may provide your brain a useful metaphor to understand the massive internal bleeding that IHN causes as it quickly attacks and destroys the internal organs of the fish.

Sources:
"Infectious Hematopoietic Necrosis Virus (IHNV)," British Columbia Ministry of Aquaculture, Food and Fisheries Web Site, 11 February 2002, <http://www.agf.gov.bc.ca/fisheries/health/IHN.htm> (25 February 2002); "Salmon in the Classroom," University of Washington, School of Fisheries Teaching and Research Fish Hatchery Web Site, 25 February 1998, <http://www.fish.washington.edu/hatchery/sic.html> (25 February 2002); George Iwana and Craig Stephen, "Disease Interactions: Infectious Disease," in Technical Advisory Team Discussion Papers Part C: Fish Health, Salmon Aquaculture Review, Volume 3, 7 August 1998< http://www.eao.gov.bc.ca/project/aquacult/salmon/report/final/vol3/vol3%2Diii.htm>(25 February 2002); "Fish Virus Discovered at Feather River Hatchery," California Department of Fish and Game Press Release, 4 May 2000, <http://www.dfg.ca.gov/news/news00/00025.html> (25 February 2002); Office International des Epizooties, "Infectious haematopoietic necrosis (IHN)," Diagnostic Manual for Aquatic Animal Diseases (2000), 9 August 2001, <http://www.oie.int/eng/normes/fmanual/A_00013.htm> (25 Feburary 2002)