Article © Ian Fuller, uploaded January 01, 2002.
When first starting keeping tropical fish the majority of people never give a thought to breeding them and their first experience comes when their female Guppy or Platy gives birth to a batch of youngsters. Watching a female livebearer deliver her young is an awesome sight the first time you see it happen and has probably been the beginning of many a lifelong journey for budding aquarists. It was certainly what started me on the road to fish breeding.
Among the many groups of fish that I have bred over the years it's the group of small armoured catfishes from South America belonging to the family Corydoradinae that have intrigued me the most and for the longest time. In fact my interest in them started within the first three years of taking up the hobby, it's an interest that has continued to this day.
There are nearly one hundred and fifty described species, with almost as many more species awaiting scientific description. At any one time there are probably twenty to twenty five species available to the hobbyist, these range in size from a little over one inch body length (25 mm), to four inches (100 mm). Their body shapes also vary, which is an indication that although they belong to the same family they do not necessarily live in the same type of habitats. Which means that providing the correct breeding conditions for them is not always a simple task. The substrate where most Cory's are found is sand and unlike common building sand, river/stream sand is different, because it is constantly being move by the flow of the water the granules have been worn rounded and smooth. In some areas there are larger gravel and in others the substrate is clay, which is not an ideal substance to use in the aquarium. In slower moving rivers, streams and flood plane pools and lakes, there may be thick layers of leaf litter or even deep silt. Therefore selecting the correct substratecan be a problem.
Water condition requirements also vary from species to species, at one end of the scale there are some that require very soft acidic water (0 - 2 dGH; pH 5.6 - 6.0) and at the other end the water needs to be medium hard and neutral (8 - 12 dGH; pH7.0). As aquarists it's almost impossible to determine the exact needs of each individual species, so we need to have to starting point. I would normally start with what I call a basic set up, the size of the tank is not that important, most of my Cory breeding tank are quite small, holding between six and eight gallons of water.
The first decision is to select the species you want to breed and here I would recommend one of the so called easier and more readily available species. Corydoras aeneus the 'Bronze Cory' and Corydoras paleatus 'Peppered Cory', there are also albino forms of both species available, which are equally as easy to breed, the ideal breeding group for any of these species would consist of two females and four males. To house them, an aquarium of 18" x 12" x 10"/12" deep (45 cm x 30 cm x 20/25cm) would be a suitable size for a breeding set up. For those of you that have a limited amount of room there are one or two dwarf species that are also very easy to breed, these are Corydoras habrosus and Corydoras pygmaeus. A small 10" x 8" x 8" (25 cm x 20 cm x 20 cm) aquarium would be an ideal size for these species.
No more than a three eighth of an inch (10 mm) layer of smooth grained sand should be used as a substrate for the larger species and about half that for the dwarf species. The reason for the shallow depth of substrate is so that when the adult fish are sifting through it in their constant search for food, they can actually penetrate to the base of the aquarium. Which alleviates the risk of uneaten food causing pollution problems. By way of filtration I would recommend the use of air driven sponge filters, these once they have matured not only do they help to keep the water clean with their biological action, but provide what can only be described as a dining table for small fry. To mature new filters I set them up in an already established tank, usually the stock tanks that house the fish I want to breed.
The only other additions I would add to a breeding tank would be either a floating spawning mop, constructed out of synthetic 4ply knitting wool. To make a spawning mop simply take a piece of stiff card about 18 - 20 cm wide and wind the wool around it fifty times. Tie off the loops at one end of the card and then cut through the strand at the other, attach a piece of cork to the tied off end and you have a spawning mop. The colour of wool is immaterial but I find that dark green or brown seem to be favoured more than any other colour. Once the mop has been soaked it will provide an ideal egg deposit site. Java moss and Java fern also make good spawning sites; both plants are hardy and will tolerate being moved from tank to tank as required.
A new breeding tank set up will have thin layer of well washed sand, water will be taken from the stock tank that the potential breeding stock are housed in, filling the tank to about three quarters full and toped up with new water of the same temperature. One or two sponge filters are added depending on the tank size and the species to be housed. The temperature is set to suit the species to be bred and then the tank is left to settle for a couple of days. For C. paleatus the temperature would be set at 70° F (21° C), for C. aeneus a little higher at 75°F (24°C), once the tank has settled the adults are introduced. If the water parameters in the stock tank are different to those in the breeding tank the adult fish should be acclimatised, which is done by catching the fish and putting them in a container with water from the stock tank and floating it in the breeding tank. The water in the container is then slowly exchanged for water from the breeding tank; once the acclimatisation has been achieved the group of adults can be released.
Now the potential breeding group need to be given the best diet possible get them into the best possible condition for breeding. A staple daily diet of a quality flake or tablet food alternated with live or frozen foods. Daphnia, Tubifex, bloodworm or Cyclops would be ideal.
Thirty percent water changes should be make twice weekly to keep conditions at there best, making sure to siphon all the fish waste and any debris that has accumulated on the bottom. In many cases when the fish are in the best possible condition a basic water change will be enough to trigger them into spawning mode, some species however will need a little encouragement, which may be achieved by a fifty percent water change using replacement water that is about 10° F cooler (6.5° C). Other species may prove even more difficult and daily water changes may be needed to start spawning interest. It's usually at this point that I advise people to make notes of what they are doing and to record all relevant details, such as tank size, water parameters, food and feeding regime, water changes; how often, how much and temperatures etc. Another tip here is to only ever change one parameter at a time because by altering more, one thing could counteract another.
It will be pretty obvious when the fish are interested in breeding buy their increased activity, what usually happens is the males will start to pay a female a lot of attention by performing little dances around and all over her, often offering themselves in arched sideways stances in front of her. They will stay in constant contact in an attempt to arouse a female's interest. It may only be one two or all four males taking part in the ritual each one competing for the chance to mate. The females will be more interested in cleaning various sites around the tank in readiness to deposit her egg/s. When a female is sufficiently aroused the roles are reversed and she will pursue the male of her choice, nuzzling into his side just above his ventral fins. At this point the male will clamp the females barbels to his side using his pectoral fin spine, the male will be seen quivering for a second or two before releasing his grip on the female. This is what is known as the Corydoras 'T' mating position and depending on the species is the time when the female releases egg/s into a pouch formed by clamping her ventral fins together. There are some species where the female releases her egg/s into the pouch after the male has released her. There is a lot of conjecture how or at what point the egg/s are fertilised and has been the subject for some lengthy discussions, which I do not intend to delve into here.
After mating the female will rest momentarily and then swim off in search of a suitable site to deposit her egg/s, which may be on the tank glass or on one or all of the other tanks furnishings. I have found that C. paleatus seem to prefer the tank sides to deposit their eggs on, with C. aeneus having a preference for plants and mops. Egg size varies form species to species; the smallest I have measured was from Corydoras pestai at 0.7 mm diameter and the largest from Corydoras 2.8 mm diameter. The size and the quantity of eggs seem to be related, a species laying small eggs produces large numbers and a species producing large eggs only produce small numbers. Once the spawning activity has ceased it is best to remove either the adults or the eggs to avoid any possibility of the eggs being eaten, if there are a large number of eggs it is best to remove the adults and return them to their original stock tank. A small number of eggs can be housed in a small container left floating in the spawning tank, where eggs have been deposited in the mop or on the plants it's a simple case of lifting the whole plant or mop out and putting it in the container. Eggs that have been placed on the tank sides can be carefully lifted by using a razor blade, some species produce very sticky eggs that are quite difficult to remove and others have hardly and adhesion at all. Eggs that are removed should be put in a small hatching container (I use 1,5 or 2 litre ice cream tubs) with water from the spawning tank and with an air stone added. If the container is floated in the spawning tank it will be maintained at the same temperature. The addition of a propriety anti fungal solution will help keep any infertile eggs from contaminating the fertile ones.
Over the four or five day gestation period the water in the container should changed for water from the spawning tank, which will reduce the content of the anti fungal solution to zero by the time fry start to emerge from the eggs. Once the fry have escaped the confines of the egg membrane it will take a further two to four days for them to become free swimming, the daily water changes should be continued. When the fry can be seen to have totally absorbed the contents of their yoke sac they will need to be supplied with food and there is nothing better to start them off than small helpings of micro worm, here the term little and often should apply but this is not always a practical option. Therefore feeding twice a day will suffice making the daily water change before the second feeding. After two days of micro worm other foods should be introduced, preferably live food, newly hatched brine shrimp or cyclops are ideal. Pre-soaked powdered flake can also be given alternating with the live food. At this time it will be necessary to increase the amount of water changes to before each feeding.
Corydoras paleatus fry grow very quickly and within four or five week the fry will need to be moved to larger accommodation and by the time they are ten weeks old they should be about one inch in body length.
Finally do remember to keep notes because not everything you do will go according to plan and the record you keep may be invaluable at a later date.
Back to Shane's World index.