Listen up, fish farmers, here's what you need to know about Infectious pancreatic necrosis, or IPN for short: It's a highly contagious disease, caused by a virus in the Aquabirnavirus genus, which will infect your young salmonids. Depending on the strain of virus, the host, and the environment, you'll be looking at anywhere from a 10% to 90% mortality rate among your juvenile fry. Older fish don't seem to die off as much-- but they still carry the virus and pass it on to their eggs.
IPN is found in rainbow trout (Oncorhynchus mykiss), brook trout (Salvelinus fontinalis), brown trout (Salmo trutta), Atlantic salmon (Salmo salar), and several Pacific salmon species (Oncorhynchus spp.). However, the IPN virus, and types related to it, have been found in farmed yellowtail (Seriola quinqueradiata), turbot (Scophthalmus maximus) dab (Limanda limanda), halibut (Hippoglossus hippoglossus) and Atlantic cod (Gadus morhua). It's also been detected in estuarine and freshwater species such as (Misgurnus anguillicaudatus) and pike (Esox lucius) .
In Scotland, IPN is epidemic. From its presence on 30% of marine salmon farms in 1997, to 45% in 2000, IPN now infects 82% of salmon farms in Scotland. Escapees from these farms are carrying it into the wild.
What to look for:
If you happen to find
lesions and
ulcers in the
pancreas,
esophagus and stomach of your fish, or its intestines empty or filled with clear mucus, there should be fish disease alarm bells ringing in your head.
The virus is passed from fish to egg, and also from fish to fish via the water. There is no treatment, and no vaccine. (However, vaccination against bacterial diseases might reduce the susceptibility of fish to this infection). A reduction in population density of your farm may reduce overall mortality.
Some analysts consider it more serious than infectious salmon anemia. It is temperature resistant: Temperatures of 55 degrees C which can disinfect against ISA have no effect on IPN-- which requires a temperature of 80 degrees C to be eradicated. It's also tolerant of low pH, which means birds and mammals who eat infected fish, can carry the virus intact through digestive system. IPN is very hardy: it is 100 times more resistant to UV radiation than a virus like infectious hematopoietic necrosis.
Disinfectants work in removing the virus from egg surfaces and from surfaces in fresh water-- although with reduced efficacy in salt water. The major problem here is that disinfectants can't reach the virus passed from adults into the eggs.
Fish farms are the largest reservoirs of the virus. Equipment and materials, water, or fish transferred between farms have carried the virus with it.
Sources:
A. Herfort. "Infectious Pancreatic Necrosis," Aquatic Animal Diseases Significant to Australia: Identification Field Guide. Australian Government Department of Agriculture, Fisheries and Forestry. Canberra, 2004.
<http://www.disease-watch.com/documents/CD/index/html/fv035ipn.htm> (3 April 2006)
Murray AG, Busby CD, Bruno DW. Infectious jpancreatic necrosis virus in Scottish Atlantic salmon farms, 1996-2001. Emerg Infect Dis serial online 2003 Apr. <http://www.cdc.gov/ncidod/EID/vol9no4/02-0311.htm> (3 April 2006)
Don Staniford. "Salmon Farming's "Foot-and-Mouth" -- Scotland's Secret Disease Epidemic Exposed." The Salmon Farm Monitor.1 June 2004. <http://www.salmonfarmmonitor.org/pr010604.shtml&g; (3 April 2006)
Fisheries Research Service. Final report of the Aquaculture Health Joint Working Group subgroup on infectious pancreatic necrosis in Scotland. 95 pages. Aberdeen, December 2003. <http://www.marlab.ac.uk/FRS.Web/Uploads/Documents/IPNSubgroupReport.pdf> (15 July 2004)
Office International des Epizooties, "Infectious Pancreatic Necrosis," Diagnostic Manual for Aquatic Animal Diseases (2000),
September 3, 2003, <http://www.oie.int/eng/normes/fmanual/A_00025.htm> (3 April 2006)
"Infectious Pancreatic Necrosis (IPN)" Schering-Plough Aquaculture Product and Disease Directory. <http://www.spaquaculture.com/default.aspx?pageid=532> (15 July 2004)