Blotchy Bass Syndrome Virus

Q: A Largemouth Bass caught by an angler. It displayed unique black markings, different from the normal pattern of the bass. Do you know what this can be?

Photo from https://lancasteronline.com/news/local/blotchy-bass-syndrome-has-affected-local-fish-for-years-studies-continue/article_eb3af286-0d14-11ed-b330-fbc42889c30d.html

A: Black markings (hyperpigmentation or melanosis) in fish can be a common response to encysted trematodes (flukes) or tapeworms, and sometimes fish change colour after bacterial illnesses. In this case this is an emerging Adomaviral disease of bass called blotchy bass syndrome virus. Bass may be found in clusters, which supports the transmissibility of this syndrome.

While most of the detections are in the United States, blotchy bass syndrome has been reported by anglers in Ontario but never formally diagnosed:

Blotchy bass or other sick fish can be reported through the finfish health tracker, which reports to appropriate authorities:

https://cwhc.wildlifesubmissions.org/#/finfish-en

For more information, please look at these links

Angler’s Atlas (anglersatlas.com)

Presentations on the surveillance efforts in the USA

Establishment of a biosurveillance network to investigate the disease ecology and biothreat of the novel, emerging adomavirus associated with blotchy bass syndrome in black basses – Clayton Raines

Investigating blotchy bass syndrome in black basses | U.S. Geological Survey (usgs.gov)