In the winter of 2013, Decorah Fish Hatchery Biologist Brian Malaise made an interesting discovery during his morning rounds. One of the ponds’ rainbow trout leapt from its enclosure overnight, stuck to a nearby barrier, and froze solid. Usually, I hate fish sticks. But for this? I’m willing to make an exception.
Ridiculous as the story is, our friend here learned an important lesson about thermal conductivity from his mistake. Well, maybe not. But we are going to learn an important lesson about thermal conductivity from his mistake. At first glance, the trout appears to be stuck to a concrete wall, but Malaise explains that the structure in the photo is actually a “baffle,” a special vane that keeps fish habitats spick and span. The important bit? The baffle is made of aluminum.
Metal is a superb thermal conductor, meaning that heat is able to pass freely through it. You’ve probably experienced this first hand (no pun intended) by grabbing a metal-handled pot after it’s been on the stovetop. What does that have to do with frozen fish? In this case, everything.
When objects of different temperatures come into contact, they want to achieve thermal equilibrium (the point at which one is no longer warmer than the other). It’s this heat transfer that led the trout straight to Davey Jones’ locker. The moment the surfaces came into contact, the metal robbed the fish it of its body heat. And because aluminum is so conductive – it’s one of the most conductive common metals – the transfer happened fast enough to freeze the fish’s water-coated skin to the baffle. Sound familiar?
“It doesn’t happen a lot but it has happened before,” Malaise adds with a chuckle. “It was still surprising. You just kind of have to laugh to yourself and say, ‘well, that’s a horrible way to go.’ I mean, that didn’t happen instantly … the fish basically freeze-dried.” Had the incident not happened after-hours, the team would have come to the rescue (a quick splash of warm water usually does the trick).
If you’re wondering why a trout would play fish-out-of-water in the first place, it’s a great question. And as in most cases of strange animal behavior, the answer is food. “It might be winter, but there are still insect hatches here,” explains Malaise. “We keep the water temperature at 47 degrees Fahrenheit, so there are aquatic invertebrates around. Sometimes the fish see movement above, think it’s a bug, and jump.”
Hey, you win some, you lose some.