Fish with yellow bumps… everywhere!!!

A black-nose dace with large yellow bumps on its belly.

In our last post we shared a video about hellbenders as “water detectors”. Other species (especially mussels and macroinvertebrates) can also help us detect problems in freshwater habitats. So when our science team is surveying for hellbenders in the wild, we make note of anything unusual we find. Last summer, we were wrangling hellbenders with Eric Chapman in western Pennsylvania, when he caught a fantail darter in his net. Darters are pretty common little fish (though some species are endangered) but there was something very unusual about this one – its belly was covered with yellow bumps! Eric had been surveying these streams since 2005 and had never seen anything like it.

So we made a plan – Eric would collect more bump-covered fish (if he could find them) during his next stream survey, ship them to me, and I’d work with the National Zoo’s pathology team to try to determine the cause of the bumps. I was concerned that we might have missed our only chance to solve the mystery, since we released that first bump-covered fish back into the stream. But when Eric returned 3 months later, he found them everywhere. He collected nearly 40 fish with these trange bumps in a single day! And it wasn’t just fantail darters – Eric also found yellow bumps on black-nose dace, emerald shiners and creek chub! Do these prolific bumps indicate a serious problem in the stream environment? Could they be somehow related to the hydraulic fracturing occurring nearby? Or is this a new disease that could potentially wipe out entire fish populations? Maybe. But then again, perhaps the bumps don’t bother the fish at all. They could be caused by some harmless little parasite…

As I’m writing this, the zoo’s head pathologist, Dr. Tim Walsh, is taking his first look at the specimens Eric collected. So stay tuned – in a few weeks we hope to know whether these bump-covered fish are a sounding alarm for an unhealthy stream… or simply eyesores.


  1. D.D. says:

    Such a busy team of researchers! Keep up the good work to monitor our stream quality!

  2. […] the help of the National Zoo’s pathologist, Dr. Tim Walsh, we solved the mystery of the yellow bump-covered darters! Official diagnosis? Grubs. That’s right, the good ol’ encysting fluke worm also known […]

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