Bronze
Catfish Fact Sheet
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.
Size
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.
Water
Conditions
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 certainly would not recommend this. At high pH levels, ammonia becomes very
poisonous. Generally 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).
Cleanliness
Bronze 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.
Temperature
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.
Breathing
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.
Food
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.
Scavenging
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. However, 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.
Companions
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.
Albinos
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.
Coloured
Catfish
A few 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
will not stock these fish.
Venom
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 40 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.
Sexing
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.
Breeding
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.
Fertilization
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.
Pest 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.
Common Names
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.
Scientific
Names
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
Fishbase: "http://www.fishbase.org/Summary/speciesSummary.php?ID=7777&genusname=Corydoras&speciesname=aeneus&AT=Corydoras+aeneus&lang=English">http://www.fishbase.org/Summary/speciesSummary.php?ID=7777&genusname=Corydoras&speciesname=aeneus&AT=Corydoras+aeneus&lang=English
Trade-off between digestion and respiration
in two airbreathing callichthyid catfishes Holposternum littorale
(Hancock) and Corydoras aeneus (Gill). http://www.springerlink.com/content/001v53470g046887/.
