Introduction to Corydora catfish:
Corydoras, or Cory Cats as they are sometimes referred to, are a family of small moderately-armored catfish from South America found throughout the Amazon River system. There are countless varieties of these fish, some of which are very hard to distinguish from each other. Most achieve a size between 1.5” and 3”, a few species stay under 1”, and there are at least five species can reach the 5” mark.
When feeding these catfish, a sinking food should be offered. Flake food that is offered to other tank-mates, while welcomed by the Corydora, is not suitable as most flakes tend to be eaten by other fish before it reaches the bottom. If it does reach the bottom, it becomes so water-logged and messy that it may create more problems than benefit as a food source. Corydora's mouths have a downward-point to them meaning that sourcing their food from the substrate is necessary. These catfish are omnivores and will happily eat most catfish wafers, small bloodworms, brine shrimp, small catfish pellets, and daphnia. Pelleted food is a great choice as it provides access to all the necessary nutrients specific to the species. Offering frozen bloodworms supplies a rich source of protein and a feeding response that is rewarding to witness. There are more choices than ever in regards to finding Corydora formulated sinking pellets that will fill their nutritional needs perfectly.
When thinking about adding some of these catfish to your aquarium, a few considerations should be made as regards to your tank set-up. Corydoras do best when swimming and feeding over a sand bottomed environment. Volcanic ash planted substrate is also perfectly suited. Both of these options offer a softened grazing area which will keep the fishes barbels in a healthy condition. Barbels are whisker-like appendages that adorn a catfish’s mouth. They aid in finding food, house the taste buds of the fish, and are used to search for food in murky water. Rough gravel is very hard on these fish as the constant grazing behavior wears the barbels down and causes them to die off. Barbels can grow back in healthy fish in approximately 4-7 weeks if the gravel is removed or the fish are moved to tank with the proper type of substrate.
Corydoras are not overly sensitive to temperatures. Ideally a temperature of 78 degrees should be targeted, while a temperature that is very stable is of most importance. There are species that require cooler water, while others do better in warmer water. Without getting too specific here about water parameters, remembering that these catfishes are native to the Amazon River would tell you that they prefer soft, acidic conditions. Some species can take harder water which tend to be the more common species that have been bred in captivity the longest and are now used to slightly imperfect parameters. The recommended ph is between 6.5 and 7.0, but again, some of the more common species will thrive in a higher ph. The quality of the water is very important as these catfish are famously sensitive to high levels of ammonia and nitrites. Other areas of sensitivity are sudden changes in water chemistry. If you are over-due for a water change for example, and then perform a large one to compensate for the time when you hadn’t done one, the ph can swing from low to high quickly, which can kill these somewhat sensitive fishes. They are also sensitive to transport if the chemistry of your tank varies too greatly from the tank that they were living in.
When kept correctly, it is not unheard of for the majority of these catfish to achieve an age of fifteen if not twenty years.
More In-depth info:
Corydoras are among a group of Cyprinid fish, the plated catfish. From there, two subfamilies can be defined: the Callichthyidae are the armoured catfish, and the Corydoradinae, the actual plated catfish. None of these fish feature any scales, yet are covered by large sheets of bone under their skin. Callichthyidae, the armoured species are bubble-nest-builders and have a broader mouth at the end of their head. Corydoradinae have a small mouth at the underside of their head and, post-spawn, do not take care of their young.
Armoured catfish species generally achieve a size that is greater than that of the plated catfish. They also have a specified feature that makes them ideal for keeping in the aquarium: they can swallow atmospherical air and use the oxygen while passing the air through the intestine. This ability makes them more adaptable to living in less than perfect conditions but this adaptation should never be an excuse to keep them in water that is not optimal.
Outside of a few very mainstreamed and common species, most Corydoras are wild caught. Even though great care is taken when collecting these wonderful fish, the fish are introduced to stressors that would normally be foreign to them. Most of the time, they are collected in the “dry” season, when rains are absent and parts of the rivers are all but puddles. In these areas, there are large concentrations of these catfish waiting for the rain to give them access to the main body of water that they are now segregated from. This stress, compounded with the stress of being shipped, can make these fish overly sensitive after being imported. When bringing home your new catfish, every step should be taken to make them feel as comfortable as possible.
Males and females are easily to distinguish in adult specimens. Females appear larger and heavier. When viewed from above, the thicker pectoral fin of the male is a giveaway. These thicker fins play a vital role in reproduction. During mating, the male positions himself T-wise in front of the female and locks her barbels with his pectoral fin. This method becomes important in preventing unwanted “mingling” among different species. The form of the pectoral fin is the accepted criteria for distinguishing species that would otherwise be confused with another closely related species.
When keeping corydoras in the tank, “schools” should not exceed more than 5 individuals ideally. This number is the group size most of these catfish travel in throughout their environment. Exceptions are the “dwarfs” such as C. pygmaeus and C. hastatus which should be kept in larger groups of 10-15 fish. Others like even smaller groups, such as the beautiful C. barbatus and the “longnoses” which prefer individual areas and do not do well in schools.
As with any fish, we would encourage you to consider keeping these fish in a biotope setting. Whenever we attempt to replicate the exact conditions that fish are found in nature, we are rewarded with fish that are more colorful, get bigger, and are more “alive” than in the often sterile, ultra-clear glass boxes we tend to keep fish in today. What fish regard as clean and what we see as clean are often very different. The Amazon river, which houses the largest concentration of species on earth is so muddy and humic you would be lucky to see 2” into the water in most spots, yet the quality of water is perfect. When Corydora catfish are kept in soft water, with a sandy bottom, lots of driftwood, leaf litter, and blackwater extract, they thrive in ways that are nearly incomparable to those housed in the average aquarium. Before purchasing these wonderful fish, please take a few minutes to have a conversation with someone who has experience with keeping these fish as to make sure that the species you choose is the best suited for your set-up.