Spots and marks on catfish.

Question

Channel catfish   Hello,
I have 8 channel catfish in a 55 gallon tank, that I have been raising for about 6 months now. About a month ago, I transferred these fish from a small 10 gallon aquarium into the new 55 gallon tank along with some plastic log decor. Recently, several of the catfish have developed black markings, spots and lines, along their bodies starting from their head and down to their tail. I have been unable to identify if this is a skin disease of some kind or if it is a result of the fish bumping and rubbing on the aquarium decor. Two fish in particular are showing the exact same marks on their head and a spot on the top left of their body, just behind the head and in front of the dorsal fin. Now on to my question, are these markings a result of trauma due to hitting objects or is this a disease that I need to treat? I will attach some photos of the fish along with this e-mail to give you a better idea of what I am describing. Thank you for your time and I look forward to hearing from you.

Answer
Hi Kyle, thank you for the photo! Despite those black marks, your catfish look quite good and healthy!

My first thoughts would be that the catfish are probably bumping into decorations and scratching themselves. Some catfish species seem to have quite delicate skin where bumps and scratches quickly show up. Of course these will heal with time. One way you can know if the black marks are from injuries is if you keep a close eye on them and see if some disappear on their own.

Also make sure the water quality is at its best. Ammonia burns can create black marks like scarring on fish that take quite a while to heal.

Young channel catfish can have naturally occurring black spots as part of their coloration. But these should start to fade as they grow 12 inches and beyond.

The black markings may even be a combination of scratches from bumping or rubbing on decor as well as natural coloration.

Take note if they seem to be behaving listless or have gone off their food. The best thing you can do is keep a close eye on them, consider the things I've just mentioned and determine if it may just be a minor issue.

Let me know how they're doing and I hope this helps!
Susan~