Barbel Erosion


Fish Herder
Apr 9, 2006
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glenside, pa
Barbel erosion. Generally Cories are among the least demanding fishes. One problem with keeping Cories under imperfect conditions, however, is that their barbels may erode. The ineradicable folk tradition has long been that the barbels were being "worn away" by sharp gravel. I think that a fish that was prone to suffer this way could only evolve in habitats with very fine silty bottoms, and that consequently it would have a limited distribution, whereas every stream catchment area throughout wide stretches of the Amazon-Orinoco basin has its own Corydoras species— and often two of them, co-existing side by side. How could any organism evolve so delicately mis-tuned to the varying sands and gravels of its streambed environments and yet be successful over such a wide area? If you think some streambed gravels are rounder than others, keep a 10x loupe by you and check out all the streambed gravels you can find.

Some Cory keepers feel that barbel erosion is more likely due to bacterial/fungal attack, and that it may be reversed when water conditions are improved. One mention of bacterial barbel erosion, in C. concolor, is in an article by Allen James (of archived among "Catfish of the Month (April 2000) at

Cathy Quinones posted at rec.aquaria, 3 June 1994, that her C. julii lost their barbels but regained them when their diet was improved (with tubifex); see

Bacterial infections are generally secondary. The primary culprits in barbel erosion may be skin flukes. A report of barbel "detachment" in ictalurid cats being aquacultured, which is ascribed to necrosis from gyrodactylus (fluke) infestation, is mentioned in a Massachusetts Coastal Zone Management white paper. Could these parasitic trematodes be an issue in Corydoras barbel erosion also?

My own experience suggests that barbel erosion might be related to long-term elevated nitrate levels. Some of my C. schwartzi have experienced eroded barbels when nitrates remained about 40 ppm. Is there a connection here?
Almost like an answer to these concerns, RTR posted at AquariaCentral, 30 Aug 2001:

"This particular myth has been around almost as long as I've been keeping fish, and it refuses to die.
"One of my favorite test tanks used crushed glass substrate (not kiln-softened) and a school of C. arcuatus corys (personal favorites) with fractured glass slab "rockwork". A part of the same shipment of corys went into a nearby planted tank with which I had been having problems with a high-organic substrate. After just a few months, guess which tank had barbel erosion? And a few weeks after unifying the schools, guess who started recoving their injured barbels while living over crushed glass? I had in the past experienced occasional barbel problems in corys (and Brochis-- they are more sensitive IME), and always had credited it to maintenance, and was able to clear it with good tank upkeep. That fact and loss of dwarf cichlids kept in organic-substrate tanks cured me of ever having a high organic substrate again. That problem tank was the last, and I'll never have such again.

"I don't use the crushed glass any more either. I really just set it for a temp tank for the test. In the year+ it operated, I had no problems with it, except that it grew algae. I do have some crushed black glass substrate, but it has been kiln-softened to round the sharp edges.

"Corys in the wild live over a wide variety of sustrates, from silt/mud to rocks, and they are adapted to substrate digging. You would expect some abrasion of the barbels over anything but fibrous peat (as used for killies), but if the substrate is clean, they will not suffer the secondary infections they will over polluted substrates. The secondary infections are what erode the barbels, just like fin rot does for the unpaired fins of free-swimming fish.

"They do prefer more sandy substrates, and will dig more freely in soft sand than in gravel by a wide margin. But they can be kept over either without damage, so long as it is clean, and they can suffer erosion over either if they are not.

I do not have much experience with Pictus cats, but I do know their barbels are nitrate-sensitive."
the skeptical aquarist

we often hear/say this same thing, that gravel will wear away the barbels on cories given time, so i was curious what your thoughts are on this article


Fish Aficionado
May 16, 2004
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Southern U.S.
I think it has a lot of truth in it to nitrates certainly but whether it really is okay to keep them in a sharp or rough gravel substrate I have my doubts. One problem with gravel over sand is more organic matter tends to get trapped and hidden beneath the gravel as opposed to sand where it's less likely to build up, having no cracks to slip into.

With a sharper gravel substrate also, you increase the chances of scrapes or damage to the barbels which increase the odds of the secondary infection and effects of high nitrate levels if the maintanence is neglected or poorly done.


Fish Connoisseur
Jun 18, 2005
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Fresno, CA
I agree, and the article points out several times that a main culprit is unmaintained substrate and highly organic substrate. I think he seems to be saying that the main problems are in tanks that aren't maintained, as we all know. He points out the problems seemed to come with dirty substrates and high nitrates. So it begs the question of regular water changes and vacummed substrates.

This is basically what we are told repeatedly. Deep gravel is hard to keep clean, clean substrates and water are essential to good husbandry. I think the issue of sharp rough gravel is one I don't need final resolution on, after accepting that bacterial infections are something to be avoided, and they are more likely in some conditions.

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