Warming waters sicken fishes

Cranking the heat on the planet turns up the disease dial of fishes. So pointed out Jim Winton, a fish biologist at the United States Geological Survey, at a conference earlier this week. Marine fish have enough to deal with as is–we’ve plucked them like eyebrows from the face of the Earth, shaken quiet seafloors into snowglobes of sediment, herded schools into new territories as we’ve warmed their waters, and may be spinning their sense of smell silly as we drop acid in their home reefs.

Now, Winton is warning that warming lakes and streams makes it easier for diseases to spread. Evolution has whittled fish to fit a thin temperature range. Their cold-blooded bodies rely on the ambient waters to keep them going; too much heat or chill can overwhelm and make them vulnerable to disease like we are to a cold after a week of rainy days.

Not only are fish more susceptible, but our mobile ways have added more ailments to the mix. One example is whirling disease. The trouble comes from a parasite that burrows into young trout, snuggles into the developing skeleton and nerves, and twists the inchoate cartilage and bone. An afflicted fish spins like a spastic hippie at the dawn DJ set. They can’t stop shaking long enough to eat properly, and they’re easily picked off by predators. Most die young.

The parasite comes from Europe, where it has found balance in the lake systems. But the wild rainbow trout in the Rocky Mountains have little resistance to it, and as warmer waters stress their slimy systems they can succumb all the easier.

Similar stories involving other fish and parasites or viruses play out in other water bodies across North America, but the difficulty of noticing and counting sickly fish has kept it off the radar. In this case, the parasite’s knack for playing puppetmaster has been its own undoing–the obvious change in behaviour makes infected trout easy to spot.