Q. My dealer has recently been selling what he calls "jumbo banjo cats." They are larger and, of course, more expensive then any other banjo catfish I have ever seen! In addition, unlike other banjos, they are actually kind of attractive, with a strange anal fin. What I consider the most remarkable thing about them, however, is that they shed their skin! Is that possible? Wrong question — I know it happens. Is this normal? Is there anything I should do about it? The fish are isolated in a 15-gallon tank and appear to shed on a regular basis. I own several regular banjo cats and I've never seen this happen with them. Any information would be appreciated.
A. Banjo cats, so called because their body shape looks similar to the musical instrument (in some parts of the country they are known as "frying pan" catfish), are members of the South American family Aspredinidae. The most commonly available genera are Bunocephalus and Agmus, the craggy-headed banjo cat. Although there have been some taxonomic changes (i.e., Dysichthys and Bunocephalichthys) I will refer to them under the names hobbyists are familiar with. I'm sure these are what you mean by "regular" banjos.
As for your "jumbos" with the unusual anal fin, these are favorites of mine also. The "whip-tailed" banjo cat has a unique anal fin with 50 to 60 rays, tiny beady dark eyes, no adipose fin, short fleshy maxillary barbels and a variety of attractive color patterns. They can grow to a total length of 12 inches. Known in the hobby as Platystacus, their scientific name has also been changed to Aspredo. (Naturally, as soon as you master the nomenclatural names of your piscean charges, and Latin rolls easily off the tongue, scientists do a revision and change the names.)
Said to have a more limited distribution than other banjo species, they are found in brackish water in estuaries along muddy banks. In the last few years these beauties are finally becoming available in pet shops. Because my tap water is naturally very soft, I add marine salt to the tank every other water change. The fish certainly thrive under these conditions. I also use fine sand as the substrate.
You're very observant in noticing that your Platystacus/Aspredo shed their "skin." For years I was saving this skin from species tanks of Agmus, Bunocephalus, Amaralia and Platystacus. I kept regular notes on when I would find the skin, water conditions and anything else I thought might be pertinent. I was frequently teased by my friends about the use of the word "skin" because that would denote the presence of keratin. After much testing, my friend Lee Finley found that it did contain keratin and could justifiably be called skin. Although you didn't mention if your other banjos were kept in a community tank, I suspect they are. The reason being that in a community tank containing banjos, you seldom find any evidence of this shedding process as the other tank residents eat it.
Is this normal? I think so, although it has been suggested by one catfish authority to be the result of poor water conditions or low pH. I haven't found this to be the case. Should you do anything about it? Yes. I would strongly suggest the use of a small power filter on the tank. As your "whip-tailed" banjos grow larger, their regular sloughing off of skin could clog box and sponge filters easily. As a point of interest, you might like to know that your whip-tailed banjos, Platystacus/Aspredo, carry their eggs on the under-surface of their body.