We received the photo below via social media a few weeks ago and we were asked if the fish in the photo was affected by “whirling disease” or Myxobolus cerebralis.
No diagnosis of whirling disease can be possible without a proper examination by someone knowledgeable in fish pathology despite the appearance of the fish. There are other causes of the spinal and other malformations that are more likely in the lower Deschutes River trout population.
First amongst those is trauma from electroshocking. Oregon Department of Fish and Wildlife (ODFW) has been conducting electroshocking studies in the lower Deschutes River for several years. Trauma such as seen in the photo above, although rare, is not unusual.
This fish could also have been the victim of osprey predation as a juvenile, but managed to escape.
Myxobolus cerebralishas a relatively complicated three-stage, two-host, life cycle. Part of that life cycle requires a tubificid oligochaete(Tubifex tubifex). Although the lower Deschutes River has seen a large increase in oligochaetes since the implementation of surface water draw from Lake Billy Chinook, this specific oligochaete has not been identified in either of two sampling studies of benthic fauna.
There have also been no other reports of similarly afflicted fish in the lower Deschutes River. Whirling disease tends to occur in epidemics.
At one time in the 1990s and early 2000s, there were suspicions that whirling disease might be present in the Upper Deschutes River watershed, although no publications that we are aware of substantiate that. Whirling disease is an ongoing concern and is monitored for in hatcheries.
If you find fish with an appearance similar to that in the photo above, please photograph the fish, and if possible, get it to a local ODFW office (on ice of course!).
Everyone can help prevent the spread of whirling disease (and other invasive species like New Zealand mud snails) here and elsewhere by following guidelines for cleaning waders and wading boots. Here is information on how to clean your gear: