Rainbow Trout
About 250,000 rainbow trout died in a sudden disease outbreak at an Idaho fish hatchery, a loss of about 8 percent of Idaho's annual output of catchable trout.
It was the second such outbreak of ichthyophthirius multifilis in as many years at the state Department of Fish and Game hatchery in Nampa. Officials say it likely resulted when stress from overcrowding weakened the fish, making them more susceptible to the parasite.
The outbreak happened earlier this year, but became public this week because the state agency is trying to manage remaining stocks of 6- to 8-inch fish at its five other hatcheries to make certain lakes and streams still get enough fish to satisfy anglers.
One possible change to avoid future outbreaks might be to reduce the number of fish raised at the Nampa hatchery and increase it elsewhere. In all, the state produces about 3 million catchable trout every year, among some 26 million total fish produced.
The parasites are visible as white spots on a fish's gills and skin. As their attack intensifies, fish turn on their sides as they try to scrape off the bugs. The fish become lethargic and eventually die. In the end, the parasites become so numerous on an infected fish's gills that it simply smothers.
May 8, 2007 6:42 AM | Category: Fish