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Keeping Corydoras catfish
With 150 formally described species, and perhaps more than a hundred undescribed species, the genus Corydoras offers great possibilities for fish keepers. All species are easy to care for, relatively undemanding fish with great personality. Many of them are readily bred. For the average fish keeper they are relegated to the "cleanup crew" and kept singly or in very small groups. Even under those conditions, they can be interesting fish. Kept in larger groups, they really shine and can become the focal point of a lively aquarium.
Corydoras are social fish - they should not be kept in groups of less than three. They appear to be happiest in groups of six or more. With the right selection of fish and appropriate aquascaping you can enjoy almost constant activity as they swim around a community tank.
Corydoras catfish have been kept by aquarists for over 100 years. The most popular and readily available species are Corydoras aeneus, the Bronze cory, and Corydoras paleatus, the Peppered cory. Both species are extensively bred in captivity. Long-fin and albino versions of both of these species exist. They are both are available in most pet stores, including national chains like Petsmart and Petco (in the US). Peppered corys, which are native to southern Brazil and northern Argentina, prefer cooler water; this is especially true for wild-caught fish.
Other popular species include the Panda cory (Corydoras panda), Corydoras trilineatus (often mislabeled as Julii corys) and Corydoras sterbai.
There are six species commonly known as dwarf corys. These fish get up to about an inch and a half in size. Three species are more commonly encountered - Corydoras habrosus, Corydoras hastatus and Corydoras pygmaeus. The others are harder to find - Corydoras cochui, Corydoras gracilis, Corydoras xinguensis.
Dwarf corys are some of the more entertaining species. Given their small size, it's possible to keep them in fairly large groups, so you can observe their shoaling behaviour. All except Corydoras gracilis are considered relatively easy to breed.
Corys live feed primarily on the bottom of the tank. They find food by sensing it with their barbels. Many people get catfish specifically for that reason - to clean up uneaten food. If you rely on that, your corys might not get enough to eat. It's a good idea to feed them sinking food that they will have a chance to get at before all the other fish do.
Many people suggest feeding them just before you turn off the lights at night. Once the tank is dark the corys have an advantage when it comes to getting food, because they find food using touch, not sight.
Corys do well on a mixture of live, frozen and dried foods. A high quality diet, right in live of frozen food, is important to get them into breeding condition.
Most corys prefer softer water with a pH around neutral, but this varies from species to species. If you have a specific species in mind, look it up in Planet Catfish's Cat-eLog. Corys tend to be fairly tolerant of water conditions, but you are unlikely to get them to breed unless you meet their specific water quality parameters.
Many Corydoras species are considered easy to breed. While the specific conditions vary, most will respond to a series of water changes a few degrees below the temperature of the water in the tank. Before trying to breed corys, it's important to get them into breeding condition. This usually requires a high quality diet rich in live or frozen foods.
Many people have reported that a water change coupled with a drop in barometric pressure will trigger corys to spawn. Other people have found that difficult fish will spawn when water is added from a tank with other breeding corys.
The best resource for beginners is Plant Catfish. Their Cat-eLog has an extensive collection of images. Their forum has a section called "What's my catfish?", which provides identification for unknown species. And Shane's World is a great collection of articles.
For the dedicated Corydoras keeper, there's Corydoras World. Run by Ian Fuller, one of the top Corydoras keepers and breeders, the site has a wealth of information. Most of the information on the site is subscription-only. At £15.00 (about $30 US) subscriptions aren't terribly expensive, but enough to deter the merely curious.