Some Subtle Signs that a Fish is Sick

I've kept multiple copperband butterflyfish (Chelmon rostratus) in my reef over the years

I’ve kept multiple copperband butterflyfish (Chelmon rostratus) in my reef over the years

Most marine aquarium hobbyists learn quickly to identify common warning signs of ill health in fish—white spots, excessive mucus production, bulging eyes, frayed fins, etc. But sometimes ailing fish exhibit much more subtle symptoms that are evident only to someone with powers of observation honed by many decades of experience.

A copperband conundrum

Recently, I was in a large LFS in New York. My mother-in-law is in a nursing home nearby, so I go there often. This store is very old, and I even helped start their saltwater tanks in the early 70s. They had a tank of about five copperband butterflies, and they were kind of cheap—like $20.00, which is a great price for copperbands. The fish were about 2 inches long. Two of the fish looked great, with vibrant colors, noticeably brighter than the other three fish. The colorful fish were swimming back and forth the length of the tank and really looked beautiful. The other three fish were much paler and were all hiding behind a fake plant at the far corner of the tank.

Which ones would you buy?

If you said the colorful ones swimming back and forth, you would be wrong, as those fish will die shortly. How do I know? The three fish that were behind the plant were hiding and less colorful because they were in a store in a somewhat bare tank. But besides hiding, they were also sticking their snout in between the branches of the fake plant looking for food. The more colorful fish were swimming aimlessly back and forth, looking very slightly up towards the surface. They showed no fear, and if I looked very close, I could see that they were breathing slightly faster than the paler fish and their mouths didn’t close all the way as they respired.

Now I know this is going to sound weird, but they also had a slight blank look compared to the other ones. Okay, stop laughing! With decades of experience, you can distinguish an inquisitive fish from a drugged fish. I would bet that the more colorful fish were collected with cyanide, as drugged fish often look better for a while. I would also bet that in a few days or a week, those fish will be dead.

All the fish in that tank, and in the store, had gill flukes, and that was very easy to spot as they were shaking their heads from side to side rapidly. The gill flukes would not stop me from buying one of those “paler” fish because I can cure that in a couple of days and for that price it is worth it. However, nothing could have been done for the more colorful fish, as they were doomed.


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About Jeff Kurtz

Jeff Kurtz is the Co-founder/Editor of Saltwater Smarts, former Senior Consulting Editor for Tropical Fish Hobbyist Magazine, and the aquarist formerly known as “The Salt Creep.” He has been an aquarium hobbyist for over 30 years and is an avid scuba diver.


  1. steven obiol says

    The store sounds familiar, sounds like Fish Town in Bayside.

  2. I am not saying

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