All about Catfish from Keith's Corner

We are getting a bit spoiled here at DLS having a guest blogger with such prolific knowledge of fishkeeping. Today Keith is sharing some insights into the world of Catfish, his favourite.

Keith Jackson is a retired engineer who has been keeping tropical fish for 40 years and a pond for 11. His first love is the South American family of small catfishes of the group Corydoradinae, covering the genera Corydoras, Brochis, Scleromystax and Aspidoras.

From Keith's Corner:

I am a definite pisciphile but I really love to see catfish moving around the bottom of a tank. A shoal of six or eight fish is a sight to see and if the decide to spawn then that’s an absolute bonus. So I get very hot under the collar when I hear people describe catfish as something you put into a tank to keep the bottom clean as if they were natural Hoovers! With a few exceptions, they are simply fish that have evolved to feed in the middle or bottom of the water column. They were not put on this Earth so that lazy fish-keepers don’t have to do as much maintenance!

Catfish, the Siluridae, are a very, very old group and are found right across the world. They range in size from giants found in the River Mekong (now possibly extinct) down to some really teeny species only an inch or so long from South America. Some are carnivorous, some herbivorous and the great majority are omnivorous. Some look cute as youngsters but are anything but as adults. The Red Tailed Catfish look delightful at a couple of inches but can reach around six feet and just one fish needs a tank of about 20,000 gallons to live in when fully grown. Yet you still see them for sale. Grrr!

Although not all catfish reach that size, there are still traps for the unwary novice. Most tanks will develop algae on the glass. We like to see our fish so we use artificial lighting, often designed to encourage plant growth, and sunlight flashing off the flanks of a fish as it swims can be a lovely sight. A shoal of a dozen Diamond Tetras in one of my tanks show greens, golds and many other colours in the their reflective scales but I have to clean the glass regularly or the algae takes over.

There are some natural remedies, such as shading the tank from sunlight, reducing the time the lamps are switched on and changing the water more often to reduce the amount of food available to the algae but many fish-keepers go to their local shop for advice and are told “Get a sucker-mouth.” The sucker-mouthed catfishes, sometimes wrongly called plecs, are a large family from South America that are generally found in fast-moving water. Some are herbivorous, a few can be described as opportunistic carnivores but most are omnivorous. Most do not eat algae, despite their reputation. Some do as juveniles but change diet as they mature. Quite a few are ideal inhabitants for our tanks but some are not.

Bristlenoses are an interesting group that will make some impression on algae but will need that to be supplemented with cucumber, zucchini /courgette and specialist food tablets and there should be bog-wood in the tank for them to chew on. They are readily available and quit easily bred. Note: only males develop the characteristic bristles. They are usually black with white spots or there is an albino for that is pink with yellow spots.

Beware, though, a plain brown fish with a large dorsal fin. This is most likely to be Pterogoblicthys gibbiceps – aka the Gibby Plec – and it gets much too big for anything under a six-foot tank. You will often see them in display tanks at some aquatic outlets where their despairing owners have brought them back because they’ve outgrown everything the owner has put them into. Why do unscrupulous shop-keepers sell them? They’re dirt cheap because they’re farmed for food so they offer a good mark-up. Money, that root of all evil……

You are also likely to come across several species of Corydoras catfish at most shops. They are almost all suited to tanks of two feet/60 cm long and upwards and some species (C. pygmaeus; C. hastatus; C. habrosus and C. cochui) barely reach one inch/ 25 mm so can be kept in shoals in quite small tanks. In the wild, these fish live in huge shoals so they do not show their true behaviour if kept in small numbers. They live quite a long time and are generally hardy but they cannot defend themselves – they have no teeth – and rely on their heavy rows of long scales, known as scutes, for protection so you need to choose their companions with care.

You will see C. aeneus, the bronze cory, and C. palaeatus, the spotted cory in most shops as they are bred by the thousand. They, like all corys, should be alert and frequently disturbing the bottom on the lookout for food. Their bodies should look robust and their stomachs should be flat, not hollow. If they don’t look ‘right’, go elsewhere – which is the mantra for every type of fish!

Suitability of water temperature is another thing most people don’t associate with ‘tropical’ fish but can be important. Taking the cory family again, you find them and their kin from the north of South American down to Argentina. That far south some species live in stretches of water that have ice on their banks! As examples, I keep Corydoras sterbai – quite a common sight in shops – and that needs temperatures of at least 25 °C to spawn. I also keep a less-common species, Corydoras nattereri, and that stops spawning if the temperature rises over 23 °C.

The advice for catfish, as it should be for any type of fish, is to do your research first. Nobody does that all the time and we all end up buying something unsuitable from time to time but if we did that more we’d have a lot less fish-keeping headaches!