Starting with Corydoras

Ian Fuller

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 there?
1. Corydoras pygmaeus and Corydoras hastatus are the smallest described species, at twenty-five millimetres, with Scleromystax barbatus possibly the largest at one hundred millimetres.



Corydoras pygmaeus

Corydoras pygmaeus

Scleromystax barbatus

Scleromystax barbatus


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. griseus.


Corydoras xinguensis

C. xinguensis

Corydoras griseus

C. griseus

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.


Box Filter

Sponge Filter


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.


Corydoras metae=young male  

Corydoras metae

 Corydoras melini=male

Corydoras melini


    Corydoras rabauti

Corydoras rabauti 


    Corydoras paleatus=male albino

Corydoras paleatus (albino)


    Corydoras trilineatus=male

Corydoras trilineatus

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 fish.

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).


Corydoras with deformities

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.


Corydoras with good barbels

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 feeding commences.

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 patterns. 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.


Corydoras undulatus=pair:male on left


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 fan shaped.


Corydoras barbatus=pair,male to front  


Corydoras melinistius=male

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 images: Danny Blundell
Rest of images by the author
© Ian Fuller @CorydorasWorld





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