The Bronze Catfish, Corydoras aeneus, is probably the most popular of all the aquarium catfish. It comes from South America from both tropical and subtropical areas, and in the south its range extends into warm temperate areas.
The countries it is native to are Argentina, Bolivia, Brazil, Colombia, French Guiana, Guyana, Paraguay, Peru, Suriname, Trinidad and Tobago, Uruguay and Venezuela. It has been introduced to Hawaii and possibly to other places.
The Bronze Catfish will grow to about 5 centimetres (2 inches) long. The females get bigger than the males. They can live for up to 10 years.
In the wild the bronze Catfish lives in soft, slightly acidic water conditions both in still and moving water. In captivity it has adapted to a surprisingly large variety of conditions. I have even heard of them living apparently healthily with a pH of 8.5. I do not recommend this. At high pH levels, ammonia becomes very poisonous. I would suggest a pH range of between 6.2 and 7.5.
They can also adapt to a range of hardness, and can take up to about 25 degrees of general hardness. However, Bronze Catfish are intolerant of high levels of salt. 600 parts per million does not seem to worry them, but beware of letting the salt level get too high. I suggest a minimum aquarium size of 60 centimetres (2 feet) long, and a minimum volume of 40 litres (10 gallons).
Catfish are sensitive to the types of pollutants that can build up in aquariums
like ammonia, nitrite and high levels of bacteria. Regular partial water
changes are recommended for this, and for other fish.
The normally recommended temperature for the Bronze Catfish is between 22 and 28 degrees C (between 72 and 82 degrees F). However, my experience with this fish indicates that they have quite a wide range of temperature tolerance. This is not surprising when the wide range of places it is native to is considered. The Bronze Catfish can by found as far south as Buenos Aires. The climate of this part of Argentina is warm temperate, not sub tropical. In fact my experience suggests that you are more likely to have trouble at high temperatures like 28 degrees C than you are at low temperatures like 18 degrees C. The Bronze Catfish also seems to be better able to survive rapid drops in temperature than most tropical fish.
The Bronze Catfish, in common with the others in its genus, can breathe air as well as water. You will often see them darting to the surface and going straight down again. When they do this they have taken in a gulp of air. The Oxygen is adsorbed by the fish’s intestine. In well Oxygenated water they only do this infrequently, but when the Oxygen level starts to get low, they each may be darting up as often as once every one and a half minutes. If this is happening it is an indication that the aquarium water is short of Oxygen. This needs to be fixed quickly.
If the tank is well oxygenated, the bronze Catfish gets a gulp of air between 1 and 3 times an hour. This is necessary to move the food through its lower intestine.
The Bronze Catfish is an omnivore. In the wild, just as in the aquarium, it eats both animal and plant material. However, the digestive tract of this fish is quite short compared with the size of the fish. Also the back part of the intestine is modified to absorb Oxygen. This means that this fish is not able to extract as much nutriment from plant material as fish like the Bristlenose catfish or the Molly.
So a reasonable amount of animal based food is necessary for Bronze Catfish. In the wild this will consist of things like small worms, crustaceans, and insect larvae. This can be mimicked fairly easily in an aquarium by feeding your fish the occasional serve of Daphnia as well as frozen or live Bloodworms, Brine shrimp etc.
Good quality sinking pellets are a useful food for your Corydoras Catfish. Make sure they have a variety of food. Algae wafers are relished by these catfish as well as many other fish.
Bronze Catfish are not specialized for eating algae. This does not mean that they never eat any, and I have observed a Bronze Catfish eating a piece of an algae filament.
The main place these fish get their food is from the bottom of the tank. This means that some of their food is what the other fish have missed. In this sense, they are a useful cleaning fish, but having some of these catfish should not be used as a substitute for normal aquarium maintenance.
Some Bronze Catfish learn to come to the top when food is put into the aquarium. They will be feeding upside down. The Bronze Catfish seems to have only a limited ability to feed in mid water.
In the wild Bronze Catfish are often found in schools of 20-30 fish. This is normally impractical in a home aquarium, but it is preferred to keep a group of 5 or more of these fish rather than just one.
They are a very peaceful fish and do not go out to catch other fish. If a fish is on the bottom and dying, the Catfish may eat them. They will also eat baby fish which are on the bottom of the tank and not yet free swimming, and they will eat fish eggs.
They will go with a very large variety of fish, including all the tetras and the common barbs, smaller Gouramis, Siamese fighting fish, Goldfish, and the many other similar fish. You will need to avoid very large or aggressive fish.
As well as the normal bronze or slightly greenish colour, an albino form of this fish has been developed. In my own experience the albinos are not as hardy as the normal coloured ones. This is not the only species of corydoras with a commercially available albino form, but it is the most common one.
years ago there was a trend for some unscrupulous suppliers to inject certain
types of fish with coloured dyes. This was bad for the fish, and most
retailers in Australia and the United Kingdom will not stock these fish.
The Bronze Catfish is an exceptionally well protected fish. As well as their armoured plates, they have spines. The one near the dorsal fin can actually deliver a low grade venom. Is a person is pricked on the skin by this spine, the pain is worse that a simple prick would be.
I have kept these fish for over 50 years and have never been pricked. We have also been selling fish for over 20 years and no one has been pricked in our shop, so it is not something that is likely to happen all the time. I suggest that you do not pick up a Corydoras Catfish with your hand.
Although no one has been pricked in our shop, one of the boys working for us was pricked by one of his Bronze Catfish in his own aquarium at home. He thought it was dead and tried to pick it up. The fish stung him through his finger nail, near the base where the nail is thin. A couple of days later he woke up with the most intense pain he had ever experienced. The sting had become infected. Antibiotics worked very quickly and he was all right.
Bronze Catfish do not go out trying to catch other fish, but if a bigger fish tried to eat one, it would probable get painfully stung.
The female is a little bigger than the male, but the shape is a better way of telling the sexes apart. The female gets a bigger belly, and if looked at from above the female is clearly wider than the male.
The male has a longer and more pointed dorsal fin.
The bronze Catfish is probably the easiest fish of its genus to breed. The parents to be should be well fed for a while before breeding. It is common to use two males and one female for breeding. In the wild this species will breed at the start of the breeding season. A drop in water temperature will often stimulate the breeding. This drop can be as much as 4 degrees C. Some people go further and lower the temperature by sprinkling cooler water over the surface of the water to simulate heavy rain.
This fish is an egg placer. The female carefully cleans a number of places for the eggs. These places may be on the sides of the aquarium, or on the leaves of plants etc.
When they are ready the breeders assume the “T” position with the female’s mouth adjacent to the male’s vent. The female takes the male’s sperm into her mouth ready for fertilization.
She lays her eggs into a little basket formed by her pectoral fins and carefully places the fertilized eggs onto the prepared places.
The number of eggs laid each time varies between 1 and 10. The breeders repeat this until the female has laid all her eggs. This may be up to 300 eggs and the spawning will sometimes take several days.
When they are first laid the eggs are nearly clear, but they darken to a golden brown. If they turn white they are infertile. Infertile eggs get fungus which can spread to healthy eggs.
Generally the eggs are separated from the parents because some people have observed Bronze Catfish eating their own eggs and young. The eggs hatch in about 5 days.
The method of fertilization used by many corydoras catfish is in dispute.
The old idea was that the sperm goes very quickly through the female’s digestive tract and comes out of her vent in exactly the right position to fertilize the eggs. It has always been recognized that there were problems with this theory. The sperm would have to pass through much faster than food normally does, and avoid being digested. Various ways were postulated to explain how this is done.
Another idea is that the sperm comes out of the gill covers of the female and are directed backwards in the right general direction to fertilize the eggs. Reading forums, you can see that there are people who adamantly insist that one or other of the theories is correct. The supporters of both sides are experienced breeders who have carefully observed the spawning of Bronze Catfish.
Personally I think the second theory is more likely to be correct.
Raising the Fry
After hatching the babies will live on their yolk sac for 2 or 3 days. They will then eat infusoria and fine fry food including Microworms and other very small live food.
Spread of the Bronze Catfish
The Bronze Catfish has a wide natural distribution, being found in at least 12 different countries and several separate river systems.
The Amazon and Orinoco river systems are connected by at least 2 natural connections. The Casiquiare River is a tributary of one of the major tributaries of the Amazon, but also a distributary of the Orinoco. There is also another connection further down the river. These would allow a fish to go from one river system to the other. Probably more easily from the Orinoco to the Amazon rather than the other way, but either is possible. Since two known connections between these river systems exist, we can speculate that others have existed at other times in the past.
So there is no mystery about why the Bronze Catfish is present in both these major river systems, but it is also present in several unconnected river systems.
I would speculate that it is sometimes spread by its eggs. The eggs of the Bronze Catfish are very sticky and in the wild usually placed on plants. The eggs are also fairly tough and people will sometimes transfer them to a hatching tank with their finger. It seems likely that on rare occasions a bird will accidentally pick up these sticky eggs and then happen to fly to an adjacent river system. This would explain part of the wide distribution of this fish.
The introduction of any animal to an ecosystem it is not native to can disrupt that ecosystem. The Bronze Catfish was introduced into Hawaii in 1984. The effect of the Bronze Catfish on the Hawaiian ecosystem does not appear to have been separately evaluated, but the overall effect of the large numbers of introduced fish to that state has been devastating to the native freshwater fish. It is a reasonable guess that some of the other fish have been much worse in their effects than the Bronze Catfish.
The Hawaiian and Australian ecosystems are examples of the terrible effects of introduced species, and of government mismanagement of the environment generally.
Although I refer to “Corydoras aeneus” as the “Bronze Catfish”, it is also called the “Bronze Corydoras”, “Lightspot Corydoras”, “Wavy Catfish”, “Aeneus Cat”, “Bronze Cory”, “Brown Cory”, “Albino Cory’, “Gold Lazer Cory” and the “Green Lazer Cory” in English.
In France, it is called La “Corydoras vert”, La “Aeneus”, La “Fouilleur” La “Corydoras Cuivré”, and La “Corydoras Bronze”. In French Guiana it is called “Kuikui”, “Manii”, “Taya Uipila”, “Kwikwi” or “Ilikyé”.
In Mandarin Chinese it is called “ 侧斑兵鲶 ”, “ 側斑兵鯰 ”, “ 小眼兵鯰 ” or “ 小眼兵 鲶 ”.
There are similarly large numbers of names in several other languages, reflecting the popularity of this fish over a long period.
The Bronze Catfish is widespread, and there are many different species in the genus. It is not surprising that some people have collected this species and believed that it was an undescribed one. There are a number of different scientific names that have been used for this species.
The accepted scientific name is “Corydoras aeneus” (Gill, 1858). Other names that have been used include “Callichthys aeneus” (Gill, 1858) , “Hoplosoma aeneum” (Gill, 1858), “Corydoras microps” ( Eigenmann & Kennedy, 1903) and “Corydoras venezuelanus” (Ihering, 1911).
Sources and Picture Credits
Trade-off between digestion and respiration in two airbreathing callichthyid catfishes Holposternum littorale (Hancock) and Corydoras aeneus (Gill). http://www.springerlink.com/content/001v53470g046887/.
The Three Lined Catfish, Corydoras trillineatus, is one of the many relatives of the Bronze Catfish, is less common in the aquarium hobby, but is still a very nice fish. Here are a few pictures of it.
Albino catfish at Fishnet Aquarium and Pets.
Female and Male Bronze Catfish with the female above. Picture from Blue Angel Aquatics.