Heater burn is not a thing.

I’m assuming a lot of people are going to read the title and then go and yell at me on social media.

Sarcasm to one side, I have seen damage to a fish caused by the heater. A silver dollar that was behind the heater when the common plec it shared a tank with slammed into a load of bog wood and caused it to fall, pushing the heater against the fish. The dollar then thrashed around and caused itself some damage.

Have I seen burns from fish resting against the heater. No. Not once outside that example, and even then that was contact damage with no evidence of burns.

Fish have sensory nerves in their skin, that means they can feel things. Even catfsh have nerves on their underside. Fish in the wild will move toward warmer water if they’re ill, in a similar way that our bodies produce a fever, they move to cooler water when the water gets too warm. Marine fish are known to use Ocean currents to navigate, and that’s probably temperature changes. Thats all to say fish can feel hot and cold, we know they can feel pain, and trust me a burn hurts.

But heaters are so hot that the fish will get burned by brushing up against them. Yeah that’s rubbish, there is a video somewhere years back of me grabbing a heater underwater. It wasn’t comfortable after a little while, and after 30 seconds or so I let go. But there was no burn or mark on my hand. Yes the heater was on, no the water wasn’t super cold. I disconnected the thermostat to keep the heater on. The heat the heater is giving off isn’t boiling the water, and the heat is being dissipated by the water.

So when we see this long thin marks on our fish, what else can they be other than heater burn? Infections for the most. I suspect most start from a scratch, or we see a lot that follow the lateral line. But just like swimbladder, whirling disease, and whitespot, there will always be people shouting about heater burn with no evidence to speak of, stopping owners giving a better treatment option.

So what would a burn look like. It’s difficult to say, but there is one way that fish regularly get burned, and that’s sunburn, normally from a pond that fully exposed to the sun with no shade. The picture shows how that looks. For burns you’ll see damage to the slime coat in terms of thickening, and damage, reddening of the scales, and underlying injuries.

I’d still say get a heater guard, it adds an extra layer of protection, just make sure you take it off frequently to check the glass underneath.