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That Upstanding Community Tank Citizen, The Corydoras Catfish

Many people keep fish where their idea of an aquarium is where the fish are in a constant fight for survival, not only from its tank mates but from its environment as well. These keepers of large aggressive fish or African cichlids are missing the joy of what some of us call a peace and harmony aquarium, one where the fish all live in constant harmony with each other and their environment. They are not constantly moving because some fish is claiming a territory or a macho display of aggression. They are moving with the flow of the water and searching for food and good times.

One of the fine residents of these peace and harmony community tanks are the corydoras catfish. Corydoras are the most popular group of aquarium catfish. Their small size and gentle nature has made them popular with aquarists for over a hundred years. They were first introduced into the hobby in Europe during the 1880's, and their popularity has continued to grow. They won't bother even the smallest most delicate species. In addition, they have armor plates on their body and stiff spines to ward off some of the more aggressive fishes. They can be kept with most fish. Best not to include then as residents in aquariums with aggressive fish, or in aquaria requiring brackish or extremely alkaline water.

There are between 130 and 140 known species of Corydoras. The published literature say all of them come from South America, where they range from Argentina to Colombia, with most of them coming from the Amazon basin. Our own local catfish expert, Col. John Peterson says that he has seen Corydoras in Costa Rica and as far north as Honduras. They range from one inch (2 1/2 centimeters) (Corydoras hastatus and Corydoras pygmaeus), to five inches (12 cm.) in length (Corydoras barbatus), but most species are around the two to three inches (5 to 7 cm.). They are mostly brownish or grayish in color, with various patterns of darker spots, stripes or bars, and some species also show a metallic greenish hue. Most come from fairly soft, pH acidic, virtually salt free waters, but will adapt to harder, more alkaline water.

One interesting characteristic that they possess is the ability to utilize atmospheric air, an adaptation that enables them to survive in waters of low oxygen content. Corydoras are able to absorb the atmospheric oxygen through the capillaries in their intestines. They can frequently be seen making a mad dash to the surface for a quick gulp of air, which they then swallow. Occasionally, you will see them excrete bubbles as the air passes out of their intestines. This ability to utilize atmospheric oxygen allows Corydoras to exist in water conditions that will kill other fish. This doesn't mean you should allow your tank's conditions to deteriorate to that point though.

Contrary to what you may have heard, most catfish do not eat fish waste! Corydoras are no exception. They are bottom-dwellers, feeding upon any small food items that they come across as they forage around in the substrate. They need good quality foods, just like the rest of your fish. I feed mine flakes, sinking tablets, live black worms, live brine shrimp, live daphnia, frozen blood worms (midge fly larva), and frozen brine shrimp. Regardless of what you feed, make sure some of it is getting to the bottom of the tank. Otherwise, your poor catfish will go hungry.

The most widely available and easiest to breed species are Corydoras aeneus and Corydoras paleatus. Both species are available in an albino form. Either of these species is a good choice for your first Corydoras catfish. They are extremely hardy, and they have been tank bred for so long that they will adapt to practically any water conditions. They have been kept in soft to very hard water and pH ranging from 6.0 to 8.2. They will live in temperatures between 68 and 82 degrees, so long as sudden changes are avoided. I have read accounts of them surviving with the salt content up to 2 teaspoons per gallon, but I would definitely not recommend this.

Once you have mastered keeping and breeding these "easy" Corydoras, you may want to keep an eye out for some of the more rare and difficult species. It used to be difficult to find the different species of Corydoras. Other than the Corydoras aeneus and Corydoras paleatus, you could usually find Corydoras trilineatus (often misidentified as Corydoras julii), Corydoras punctatus, Corydoras melanistius, and occasionally Corydoras arcuatus. There weren't many others available. The situation has gotten much better in the last few years. I know in the Tampa Bay area, there are currently at least 20 species of Corydoras available. I believe the increasing popularity has allowed importers to locate and ship species not previously imported.

The challenge of these new imports is in getting them to spawn in the aquarium. Many species haven't yet been bred in the aquarium, and demand a high price because of it. I try to make my water conditions as close as possible to those where the fish come from. Often, this requires some research, to find out which rivers they come from, and what the water conditions are in their home range. Duplicating these conditions is sometimes enough to get them to spawn. Other tricks I have used are waiting until the South American summer months, when the rainy season starts, and doing a massive water change with distilled water. This water should be several degrees cooler than the tank water. The idea behind this is to duplicate the rainy season, when most Corydoras spawn. Sometimes, if this doesn't work, I try waiting until a storm hits the area, then do the water change. Sometimes the drop in barometric pressure, along with the water change will work. I also use driftwood in my tanks to add tannic acid to the water. Many Corydoras come from waters high in tannic acid. You could use blackwater extract for the same effect. Often, I can't get wild caught fish to spawn despite my best efforts. This is just part of the fun (and frustration) of keeping rare Corydoras.

I've covered the basics of keeping, feeding, and breeding Corydoras. These little fishes are excellent inhabitants for the community aquarium, being peaceful, hardy, long-lived and undemanding in their requirements. They will tolerate a wide range of water conditions, eat most foods, and have been known to live for up to twenty five years in aquaria, which is a very long life span for such small animals. If you need more information, there are many good books available that will give you detailed information on the particular fish you are interested in. I hope you get as much enjoyment from keeping and breeding Corydoras as I do.

Last updated 30 June 2003, 2146, BL