What’s wrong with this catfish?

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Dr Peter Burgess helps one reader who is worried about one of his Dora catfish.

Q) I currently have two Dora catfish which I have had for around three years, which were bought as youngsters and are now about 10-12cm. For some time now, one of the fish has had raised scales towards his tail which show signs of redness and his side spines are just stumps. He seems healthy other than this, feeds well and doesn’t appear in any discomfort.

The fish are currently in a 120 l Juwel Lido tank which also includes a black Angelfish, two Geophagus and a few tetras along with a seldom-seen Orange-tipped pleco.

I have included photos to hopefully assist with a diagnosis. Any help will be greatly appreciated.

COLIN BROWN, VIA EMAIL

A) DR PETER BURGESS SAYS: I think the body reddening and historical pectoral fi n erosion is likely due to some sort of bacterial infection. I’m tending to rule out skin parasites, certainly as the primary cause, as I would expect other fish to also be showing symptoms, given that most common skin parasites of fish, such as whitespot, velvet, and skin flukes are highly contagious.

But it’s possible that your catfish is suffering from a mixed bacterial and parasite infection. Mixed infections are not uncommon. For example, a bacterial infection of the skin can attract normally harmless protozoa, such as some strains of Tetrahymena protozoa, which settle on the damaged area and begin feeding on the infected tissues (and maybe even the bacteria). In other cases it’s the reverse, a primary parasite infection is followed by secondary bacterial issue.

My advice would be to isolate this fish to a spare aquarium. I don’t see any What’s wrong with this catfish? then treat the fish with a general (broad-spectrum) anti-bacteria remedy for another week. Leave the fish in the tank for a third week and review its condition throughout. If it hasn’t improved by the end of week three, then you may need to seek veterinary advice as antibiotics may be required.

Hopefully, if the catfish is improving, keep it in isolation until the reddening has completely gone before returning it to its home aquarium. Obviously, use water test kits to frequently monitor ammonia and nitrite levels in the isolation tank as these toxic wastes can rise quickly, particularly with a largish fish. You can make water changes to keep the ammonia/nitrite levels in check, in which case remember to medicate the replacement water in order to maintain a therapeutic dose of the parasite and bacteria cures. Or alternatively you can use an ammonia-neutralising product, such as Ammo-Lock.

One question is why the problem only affected this fish and not the other catfishes, or indeed any other fish. It is possible that this fish sustained some sort of skin damage that has led to infection. If so, could the other fish be responsible for harming it? Keep an eye out for signs of aggression, particularly between this fish and the other catfish, including that elusive plec. A few extra caves may help if it looks like the catfishes are fighting over hiding places. need to medicate the main tank. Set up the isolation tank with a cave or two so the fish can hide away, but no gravel or other substrate as we want as hygienic conditions as possible. Feed the fish as normal. Syphon out any uneaten food and any solid fish wastes to help maintain good hygiene. You can install an aquarium filter, although bear in mind that the beneficial filter bacteria may be affected by the treatment you use.

I would initially treat the fish with a general protozoa cure from your aquarium store. Treat for seven days, following the manufacturer’s instructions. After that, make a largish water change of around 70-75% and then treat the fish with a general (broad-spectrum) anti-bacteria remedy for another week. Leave the fish in the tank for a third week and review its condition throughout. If it hasn’t improved by the end of week three, then you may need to seek veterinary advice as antibiotics may be required. Hopefully, if the catfish is improving, keep it in isolation until the reddening has completely gone before returning it to its home aquarium. Obviously, use water test kits to frequently monitor ammonia and nitrite levels in the isolation tank as these toxic wastes can rise quickly, particularly with a largish fi sh.

You can make water changes to keep the ammonia/nitrite levels in check, in which case remember to medicate the replacement water in order to maintain a therapeutic dose of the parasite and bacteria cures. Or alternatively you can use an ammonia-neutralising product, such as Ammo-Lock.

One question is why the problem only affected this fish and not the other catfishes, or indeed any other fi sh. It is possible that this fish sustained some sort of skin damage that has led to infection. If so, could the other fish be responsible for harming it? Keep an eye out for signs of aggression, particularly between this fish and the other catfish, including that elusive plec. A few extra caves may help if it looks like the catfishes are fighting over hiding places.

Did you know?

A whitespot treatment can be used to tackle parasitic protozoa infections, even in cases where whitespot itself is not a factor.