Catfish Conservation: Black Blotches on Bullheads: Should Catfish Anglers Be Concerned?
By Keith “Catfish” Sutton
Every now and then, an angler catches a catfish that just doesn’t look right.
For example, I caught a Mississippi River blue cat recently that was missing an eye and had an old scar across one side. I’ve seen plenty of others with mangled fins and roughed up skin, including some that no doubt were injured trying to escape an otter or turtle. Catfish are tough customers, and most of us who’ve fished for them very long have seen some pretty rough-looking specimens.
But imagine landing a bullhead catfish covered with ugly black blotches and lumpy growths. That’s exactly what anglers began seeing several years ago in a lake that straddles the Vermont-Quebec border. At first, everyone wondered the same thing: What in the world is wrong with these fish?
The answer turned out to be something no one expected.
After years of studying the fish, researchers now believe those black growths are a rare form of skin cancer that may actually spread from one catfish to another. If they’re right, it would be the first contagious cancer ever discovered in fish.
Now, before you swear off eating catfish or start worrying about the fish in your favorite lake, let’s put this into perspective.
The fish involved are brown bullheads, cousins to the channel cats many of us chase every season. The problem has been found in only a handful of lakes in Vermont, Quebec, Maine and New Hampshire. It isn’t showing up across North America, and there’s no evidence that people can catch anything from handling these fish.
That’s the good news.
The mystery began more than a decade ago when anglers started catching bullheads with strange black patches on their skin. Some fish had only a few spots. Others had growths on their lips, fins, gills and even over their eyes. Wildlife officials first suspected pollution. Others thought a virus might be responsible.
Neither theory held up.
When scientists compared the tumors from different fish, they made a surprising discovery. Instead of looking like the fish they came from, the cancer cells all looked remarkably similar to one another. That suggests the cancer itself—not a virus or bacteria—may somehow be moving from one fish to another. Exactly how that happens remains a mystery.
One possibility is during the spawning season. Adult bullheads gather in tight groups and often bump, rub and poke one another with the sharp pectoral fin spines. Researchers think cancer cells may enter tiny wounds created during all that activity. It’s only a theory for now, but it’s the leading explanation.
Interestingly, many infected fish don’t appear to be on death’s doorstep. Some have lived long enough to reach older ages despite carrying the tumors. Scientists have even found cases where the cancer spread to internal organs, but they’re still trying to understand exactly how the disease affects the fish over time.
So, what does all this mean for catfish anglers? Probably not much—at least not yet.
If you happen to catch a catfish with obvious black tumors or unusual growths, it’s worth taking a few photos and reporting it to your state’s fisheries agency. Anglers are often the first to notice when something unusual shows up in a fishery. In fact, that’s exactly how this whole investigation got started.
As for eating one? Researchers have found no evidence the disease poses any risk to people. Even so, officials in Quebec recommend not eating fish with obvious tumors. Personally, I suspect most anglers wouldn’t need much convincing. If a fish looks unhealthy, there’s no harm in putting it back or disposing of it properly and catching another.
Perhaps the biggest lesson here is that nature still has plenty of surprises waiting for us. Scientists have studied fish for generations, yet they continue discovering things nobody knew existed. A contagious cancer in catfish wasn’t on anyone’s bingo card.
That’s one reason I always encourage anglers to pay attention to more than just whether the fish are biting. Notice what you catch. Look for anything unusual. Report it if something doesn’t seem right.
You never know when an ordinary day on the water might help solve an extraordinary mystery.
(Keith Sutton has been writing about all aspects of catfish and catfishing for 50 years now. Two of his books about the sport, “Catching Catfish” and “Hardcore Catfishing,” can be purchased through his website.)
