by Yann Fulliquet, uploaded January 01, 2002
The very first time I encountered this fish, it was back in 1997, I was visiting one of the local shops and found in several tanks some rather large, probably full grown, Corydoras that I had never seen before. They were looking a lot like Corydoras rabauti, but the size was way too big to be them. I asked the shop owner about the identity of this Corydoras and he gently answered me that they were Corydoras metae. I knew they could not have been this species, so I asked him about the price, which was 8€ per fish. That was a really good price for a rather uncommon Cory, so I bought the whole stock, which consisted in 5 males and 4 females.
One of the first few things that impressed me with this Corydoras was its size, the females were around 7-7.3cm long and males were about 1cm smaller. At that time I had never seen a larger Cory. The nine fishes were placed in a 250 litre tank, filled with tap water (Ph: 7.4, Gh: 12°, Kh: 8°), the temperature was set at around 26°c, the other tank mates consisted of Ancistrus sp. and dwarf cichlids. I started to search for some information on the possible name in the “Aqualog” “All Corydoras”, no doubt about it they were Corydoras zygatus. Also, at the same time, I began to search for more information regarding this species but came up empty handed initially. Sometime later, I don’t remember when, I read that this species could lay around 600 eggs at spawning, but no other detail was given on ways to achieve breeding.
So I just went on keeping them in my tank and hoping that someday, after a water change, I would find them to have spawned in the main tank. But years passed and nothing happened, until one day I read in a magazine that a temperature of 16°C was required for make them spawn. I decided I should give them another serious try at breeding. To this end I set up a a small 10 gallon tank with a small layer of gravel, a little bogwood and some Anubias bateri var. nana. The tank was sited on the floor to have the coldest room temperature possible; no light was added to the tank except that coming from the room in which the tank was placed. I transferred the largest female along with two males. The trio was then heavily fed with frozen bloodworms and given a 60-75% water change every 2 days. I made sure that I would make the temperature sink from 20°C to 16°C. I went on for about 3 weeks with that system and one day, on my birthday to be more precise, when I came back from work, I found the tank full of eggs! They had spawned and had placed the eggs about everywhere the water current was being felt. The eggs were placed in different part of the tank in either huge clumps of hundreds of eggs or in small clumps of 10 or so. The eggs had a diameter of about 1mm. I can’t explain the joy of that sight (especially as they did it on my birthday) and I must say I could not have been more happier and what a great present from Mother Nature! Not to take any gamble, I removed the parents from the spawning tank. But tragedy struck - a day after the event, all the eggs had turned white because of they were not fertilized. I had to restart all over again.
About 3 or 4 months later I decided to give it another try This time I ensured I selected the most active and most healthy trio possible, and once again placed them in the 10 gallon tank and once again they were fed daily with frozen blood worms. Every 2 days a 75% water change was made with the tank being refilled with cool water to make the temperature sink as low as 14°C. After a week and half of that treatment, I forgot to feed the trio one day, the next day, when I came back from work, I again found a huge number of eggs in the tank. These were mainly placed on the upper part of the tank glass but all around the tank. This time I took all the eggs out and placed them in a plastic box filled with water from the tank, an air stone was added, and the whole set-up was placed in a dark place. I did check the eggs to see if they were fertile or not. I estimated that about 95% of the eggs had been fertilized. A day or two after the eggs all hatched, it was impressed upon me the unusually small size of the fry and I began to fret about how I would feed them once their yolk sac had been absorbed.
As I said, the fry tank (2 gallon) was filled with water from the parent’s tank. To this I added a little air filter mainly for two reasons. Firstly to avoid the possibility that the fry would be sucked into it and, secondly, I was also hoping that the fry would eat the small animals present on the sponge of the filter. To avoid any fungus to develop on the bottom, a small layer of sand was put in. The first food given was some crushed Spirulina tablets; the fry seemed to eat it without any problems - I did not notice any losses and the fry were growing at a rather good pace.Obviously only one female, the smallest, had taken part in the spawn as the other one looked like she was still full of eggs. The adults have not tried to eat any eggs. I did cut the leaves and put them in a little plastic box filled with water from the tank. I did not add any anti-fungus but only an air stone. I placed the plastic box in a dark place to help prevent fungus. After four days, the eggs hatched and, encouragingly, just a few had turned white. The young were acutely small, a few millimetres long. At this point there were siphoned and put in a 3 gallon tank. Into this I put some fine sand, a “Tetra Bilifilter “ and the water level was not too high so as not too kill the fry. After two days the fry completely absorbed their yolk sac. Liquid fry n°1 was given as first food. They were fed this during about four days. At this stage micro worms were given as their second food. I found the fry rather as slow growing, despite a good quality feeding and everyday water change. After two week I gave them some tablets for bottom feeders, but not one completely, just a quarter of it. Any left over were siphoned so as not to pollute the tank. When refilling the tank it is important to make sure you are replacing water at the same temperature and with the same chemistry otherwise you can kill some if not all of the fry. The rearing routine was to do a water change every day, changing about 30-50% of the water, the sponge was cleaned in the old water, and water from the parents’ tank was taken to refill the fry tank. I also made sure to clean the sand to avoid any developing of bacteria. After two weeks, there was no possible doubt about the identity of the parents, the fry look like Corydoras zygatus fry and not like Corydoras rabauti fry.
Suddenly I started to lose some fry for an unknown reason. There were no signs of fungus or starvation. At first it was only 2-3 young that had died, so no great concern, but this began to rise somewhat dramatically. One of my errors here was using, a day before, untreated tap water to refill the fry tank. I was in a hurry and forgot not to use tap water, I did use a dechlorinator on the water, but as it was springtime and, around here anyway, a time of year when water companies put a bit more chlorine in the water because of farmers using manure to fertilize their fields and so forth. In two days all my fry were gone.
Since then I did not retried to spawn them, because of lack of time and space. I also encountered my first adult losses, probably of natural causes as they were already full grown at the time I bought them so it is really hard to put an age on these fishes. I only known that I have had them now 6 years, and I would assume that they were at least 2 years old when I saw them in that shop. I shall attempt another spawning of them before I loose them; I now have only 3 males left but still have the 4 females. The biggest female is almost 8cm long.
Since I bought them I have seen only seen this Cory twice for sale, one at an importer in France and another one at an auction here in Lausanne where I live. It was mixed up with some Corydoras rabauti. These sightings were in the last 6 months, before that I had seen it anywhere. I really do want to be able to perpetuate “my” population by rearing some young from them and would also like to be able to spread this species around locally as it is really worth being kept. It is a very hardy Cory, adaptable to a great range of water chemistry and temperature. Plus its attractive colouration makes a group of them a nice addition to anyones aquarium. Anyway Corydoras zygatus will always have a special place in my heart and I will always have room for them in my tanks! If someday, you are lucky, just like me to come across this species, go ahead and go for it, they really are worth it
Since the first publication of the article in "Cat Chat", I was successful in my attempts to have one of my pairs spawn again. I managed to save around 30 fry and these are growing pretty well. I only used 1 male per female, which explains why I have not such a great fertility rate this time. I did it this way because I want to have 3 batches of fry coming from 3 different pairs, hopefully to ensure a good quality strain for the years to come.
Cat Chat, The journal of Catfish Study Group (UK) Volume 4 Issue Number 2 June 2003