ver the years I have been
asked many questions about keeping and breeding
Corydoras Catfish, by people that would like
to start keeping them and others that have them
but would like to try and breed them. The ten most
popular questions I have listed below. The answers
I have given to these questions are based on the
many years of experience I have gained with keeping
and breeding these wonderful little fishes, and
are meant as a guide rather than the rule.
1. How big do they get? 2. How should
I set up a tank for them? 3. How many can
I put in my tank? 4. What species are best
to start with and how expensive are they? 5.
Where are the best places to get them from? 6.
What should I look for when buying? 7. What
do they eat? 8. How can I sex them? 9.
Can I breed them? 10. How many species are
1.Corydoras pygmaeus and Corydoras
hastatus are the smallest described species,
at twenty-five millimetres, with Corydoras barbatus
possibly the largest at one hundred millimetres.
2. There are many ways of setting up tanks that
are suitable for Corydoras, I think the main
criteria would be what are the ingredients needed
to create the ideal Corydoras environment?
For me these would be, a) Tanks that are large enough
to house the fish you intend to keep. (See answer
3). b) A smooth substrate to prevent damage to mouthparts.
c) Quality water = Clean and aged for at least three
days, with near neutral values pH6.8 - 7.4, GH10
- 15, and a temperature of between 70º - 76º
Fahrenheit would be a good starting place. Most
water authorities supplies although they may vary
in values from one authority to another, are quite
adequate for most species.
There are two types of set up that I use. The first
is a community tank set up that is primarily aimed
at housing Corydoras, in which other fish
are added to give the tank a visual balance. External
power filters are used on my community tanks because
of the substrate I use, which is either fine smooth
gravel no larger than one and a half millimetres,
or well washed river sand which very quickly clogs
under gravel filters. The depth of the substrate
is quite shallow no more than fifteen or sixteen
millimetres deep, this allows the Corydoras to search
out food particles right down to the base of the
tank. This prevents the problem of food particles
filtering deeper than the catfish can reach and
souring the substrate.
For tank decoration I use pieces of bogwood with
either Java fern or Java moss attached, and although
the substrate is fairly shallow I have found most
plants such as Cabomba and Elodia will and do grow
well. Java fern is particularly good because it
can be attached to a variety of tank decorations,
be it wood, slate or rocks. If it is held in place
with the aid of an elastic band it will attach itself
in a very short space of time. It is a very tough
plant and will grow well under a wide range of conditions.
The second type of set ups that I use are purely
for breeding and raising fry. These tanks vary in
size from 20cm x 20cm x 20cm which house small species,
to 90cm x 45cm x 20cm which are stock /fry rearing
tanks. The size of the tank for breeding is relatively
unimportant so long as it is large enough to house
the fish that you are intending to breed. In the
small 20 x 20 x 20cm tanks I keep and breed small
species like C. xinguensis and C.
All of my breeding and rearing tanks have a ten
to fifteen millimetre layer of either river sand
or fine smooth gravel in them. I have in the past
and do still occasionally use tanks without any
substrate at all in, these are mainly for quarantining
or raising delicate fry in where uneaten food and
waste matter can be seen and removed easily with
the minimum of disturbance to fish or fry concerned.
The types of filtration used in the small 20 x 20
x 20cm tanks are sponge filters. Box filters are
used in the medium sized tanks (45 x 25 (30) x 25cm),
and in the larger 90 x 45 x 20cm stock/fry rearing
tanks the filters are home made under gravel box
types with power heads fitted. If I need extra filtration
I use an external canister type filters.
3. The number of Corydoras that can be
housed in any one tank is much a matter of choice,
but if you bear in mind that they are shoaling fish
and are generally happiest in-groups of six or more.
My recommendation would be six to eight inches of
fish to every square foot of base area. When calculating
do not count the caudal fin (tail) as part of the
fishes length its the body length that counts.
4. In the main most of the Corydoras
species that are available are quite hardy and not
too difficult to keep and maintain in good health.
Therefore the choice of species to start with will
probably have more to do with finance than anything
else. There are species such as Corydoras aeneus
and Corydoras paleatus that have been in
the hobby for many decades, these are being commercially
bred in there thousands in far eastern fish farms
and can be bought for one or two pounds each depending
on their size. At the other end of the scale there
are species like Corydoras solox and Corydoras
gracilis that have asking prices of up to fifty
pounds sterling each.
For those people that have never kept Corydoras
I would recommend some of the less expensive species,
which should be available for under a fiver each,
some of them are quite striking in their markings
and are ideal species to start with. Here are a
few to look out for Corydoras trilineatus and
Corydoras schwartzi have sharp black and
white markings. Corydoras metae, Corydoras
melini, and Corydoras rabauti have tan
coloured bodies with dark bands across the back.
Then there's one of my all time favourites Corydoras
arcuatus (the skunk catfish), with its white
body and arching black band that runs from snout
over the back to the tail. For those of you looking
to try your hand at breeding need look no further
than Corydoras aeneus, its albino form or
Corydoras paleatus, these are probably the
easiest of all Corydoras to breed.
5. There are several sources to acquire Corydoras
from some of them are better than others. The
first place to look is in your local aquatic shop
the choice of species there may be limited, but
most if not all aquatic shops will have at least
a couple of species on offer.
To find a larger choice of species you may have
to travel a little further a field to one of the
shops that specialises in catfish. There are a few
of these establishments around the country where
the choice of species will seam almost endless.
I have been known to make a round trip of over four
hundred miles in a day because certain shops have
got the species that I have been searching for.
A third source of supply is from someone that is
breeding Corydoras. The biggest advantage
with buying from a breeder is that you will know
the conditions the fish have been bred and raised
under, how old they are and the best types of food
to feed them on. This last point is something that
is almost impossible to determine with wild imported
6. When buying Corydoras there are
a number of important things to look out for, to
insure that you are selecting good quality stock.
It is probably easier to list the fish to avoid
and add the good points later. a) Sunken eyes, b)
Red blotches in the abdomen, c) hollow belly, d)
inflamed gills, e) Missing or badly worn barbels,
f) Deformities. (Pics of bad points)
Fish that have sunken eyes are old and almost at
the end of there lives. Those fish that are showing
red blotches in the abdomen have an infection in
the gut, which in most cases is fatal. These fish
should be avoided and not given a second look because
the chances are they will not survive for more than
a few days. Fishes that have sunken or hollow bellies
may survive given the right kind of conditions and
feeding. I would still leave these fish alone. Reddened
/ inflamed gills are also a sign of infection which
may or may not be easily cured, if the fish was
rare and the price was right then I might take a
chance, but normally I would leave these fish alone.
The barbels of Corydoras are very important
sensory organs used for detecting and searching
out particles of food from the substrate, and were
the females are concerned playing a major part in
the breeding activity. Badly worn barbels may result
in infection and mouth fungus so again these are
fish that I would avoid. Any fish that are showing
deformities are definitely given a miss; although
they may be perfectly healthy they may pass on their
deformities to their offspring.
Freshly imported fish quite often arrive with damaged
Finage, splits or with pieces missing out of them
in most cases the damage will grow out and is not
normally a danger to the fish's health.
Now that we've seen the undesirable fishes 'what
does a good one look like' I here you ask, well
a quality Corydoras should have. A full rounded
body, sparkling eyes, good barbels, a full set of
seven fins, the flanks and gill covers should be
covered by a metallic sheen and finally it should
be reasonably active, although there are some species
are far more active than others.
7. The choice of food is very important with
any fish you keep and not just Corydoras.
I use a variety of foods both commercially manufactured
as well as cultured and collected live foods. My
feeding program is based around a staple diet of
either a pre-soaked (so it sinks to the bottom straight
away) quality flake or sinking tablet food. The
tablets are crushed before given to the smaller
species and crushed powder fine for fry.
Live foods come in a variety of forms the following
are the ones that I mainly use, none aquatic = Microworm,
whiteworm and earthworm finely chopped. Aquatic
= Brine shrimp, daphnia, tubifex and bloodworm.
All live foods are given in small amounts, ideally
as much as the fish will eat in five or ten minutes.
There are also frozen foods that are very good especially
during the winter months when live foods can be
harder to come by, the range of frozen foods are
quite extensive from Cyclops to muscles and these
day's most aquatic shops stock them. It doesn't
hurt to try these out now and again; I've not found
any that my fish won't eat, although some may need
grating down to a size that can be consumed easily.
During the summer when daphnia is plentiful I will
collect as much as I can, drain of the water when
I get home and freeze it in plastic bags. I roll
it out flat so that it is in sheets of about the
same thickness as a medium slice of bread, (10mm
thick) this makes it is easier to break pieces off
to feed to the fish, and each bag contains enough
daphnia to feed all my fish.
Feeding takes place twice daily when ever possible.
When time permits the morning feeds will consist
of flake (pre-soaked) or tablet foods only. In the
evening the tanks that are scheduled for water changes
have this done first then the fish are fed, however
all the fry tanks have daily water changes before
8. Sexing Corydoras is not always
the easiest thing to accomplish especially with
freshly imported fishes, so I will explain how I
go about the task. To start with there are three
areas where I look or differences.
The first is colour, which is probably the easiest
area where differences will show. With most Corydoras
species there are no discernible colour differences,
but in those that do show colour dimorphism it's
the males that poses the brighter more intense colour
There is however a danger here because with some
of these species the colour differences are so great
you could quite easily think that you are looking
at two separate species.
The first thing to do is ask the retailer if they
have been brought in as the same species, if they
were then there's a fair chance that they are the
same species. I would then take two of the brighter
coloured specimens to every one of the lesser-coloured
ones. If there is any doubt then I would take equal
numbers of each. Most Corydoras species belonging
to the 'elegans' group do show colour dimorphism.
The second area I look at is the Finage. Mature
male Corydoras almost always have longer
and more robust fin spines than females in particular
the pectoral fins and to a lesser extent the dorsal
fin, with some species the differences are so small
that it is virtually impossible to see. With other
species the differences are quite dramatic to the
point were the males fins can be twice the length
of the females.
When there are no discernible differences visible
in the Dorsal or Pectoral fins the area I look at
next is the Ventral fins. If there are any fin differences
to be seen at all it will be here with males having
longer, narrower and more pointed ventral fins than
the females, which will be far more rounded and
The third and final area that I look at is the body,
when viewed from above the widest part of the females
body is at a point just forward of the insertion
of the ventral fins. In males the widest part of
the body is at or just behind the insertion of the
pectoral fins. When viewed from the side females
show a deeper more rounded body shape, were males
should look slender and far more streamlined. There
are other characteristics that can also help to
differentiate the sexes, for instance Corydoras
barbatus males have bristles on the cheeks and
females don't. So with species that are difficult
I will look for anything that can separate them.
On the occasions when I find it impossible to separate
the sexes I will buy at least six specimens or more
if the price is right. Once you have had the fish
for a while and conditioned them the sexes will
be relatively easy to separate.
9. Breeding Corydoras in it's self
is not difficult the fish do that with relative
ease all on their own, the difficult part it triggering
them to do so in the first place. There are many
conditions that need to be met before they will
breed. Some times all that is required is a change
of water of the same temperature to set them of
(Corydoras pygmaeus). The next stage would
be a change of water that is slightly cooler, five
or six degrees Fahrenheit is enough to promote spawning
interest, Corydoras aeneus, Corydoras
paleatus and Corydoras panda are typical
of the species that will respond to the cold-water
treatment. Once the basic water change methods have
been tried then things start to get a little more
difficult and other methods need to be used. The
one thing that I do when trying to encourage a species
to spawn is only try one thing at a time, this is
because the first thing you changed may have been
the right trigger. The second change may counteract
the first and put the fish off spawning altogether.
This may sound a bit like basic common sense to
many of you, but it is surprising how many people
tell me all the things that they have done to try
and trigger there Corydoras to spawn. When asked
they tell me several condition changes were made
at the same time.
I would also recommend keeping notes as in my opinion
they are invaluable especially when trying to breed
some of the more difficult species. These notes
can be referred to at any time to see the changes
that have been made, or used to help formulate a
series of changes that you think may trigger a spawning.
The following is a list of the things that I would
do in order to encourage a species to spawn given
that the fish are in spawning condition. a) A weekly
water change with no temperature change. b) Twice
weekly water changes with no temperature change.
c) Daily water changes with no temperature change.
Then a, b, and c, again this time reducing the temperature
by six to eight degrees Fahrenheit, after the cooler
water changes the same sequence would be applied
using warmer water again six too eight degrees Fahrenheit.
There are some species of Corydoras that
prefer warmer temperatures Corydoras gossei is
one of these. I will change the same amount of water
approximately fifty percent for every water change
made to maintain consistency. My next move would
be to extend the time between water changes from
one week to two weeks and then three or even longer,
first with equal temperature water then with cooler
water. If all these measures failed then I may try
reducing or raising pH values, then the general
hardness lowered or raised. These are the list of
things that could trigger a spawning is endless
as is the time needed to implement them, so I would
say the main ingredient to successful Corydoras
breeding is patience and lots of it.
10. The number of described Corydoras
species is now one hundred and fifty four, with
many more species as yet undescribed arriving in
aquatic shops all over the country almost weekly,
making the choice for customers almost endless.
Photo Credits: Top 2 pictures: Danny Blundell
Rest of photo's by the author Ian