A happy accident: breeding Corydoras gracilis

Sometimes it is pure coincidence that leads to success. Ten years ago, Robert Budrovcan was one of the first aquarists to make a breakthrough with one of the most timid and sensitive Corys, Corydoras gracilis, known as the Shy Cory. As this report attests, his success continues today.

During a tour of the facility of a renowned German importer in 2003, I found a species that caught my attention — a dwarf armored catfish named Corydoras gracilis. This small fish, which has a maximum total length of 1.6 inches (4 cm), lives in the Brazilian state of Para. It was once discovered by Hans Baensch and Heiko Bleher in the drainage of the Rio Madeira west с Itaituba, a town on the Rio Tapajos.

C. gracilis was first introduced to the trade in the late 1990s. There was a small distribute area near the city of Porto Velho in Rondonia, where the species was found in small rainforest tributaries of the Igarape Novo (Madeira system). According to Hans-Georg Evers, this forest has since been completely destroyed.

Cool and soft

Actually, I knew very little about Corydoras gracilis and it was not on my search list. My reaction to it was “Interesting…I haven’t tried this one yet,” and I ended up taking 20 of them home. The general condition of these fish was surprisingly good, and they also survived the transition to my water and tank conditions very well.

Once home, I studied my new acquisitions in more detail. These fish were really fantastic, but it turned out that in the wild, they lived in a rather cool blackwater river. They are caught only in the early morning hours, when they come out to feed in the few open areas and are easy to see and capture. Otherwise, they are hard to spot and extremely difficult to catch. I received this rather sobering information from Hans-Georg Evers, who had visited the home of my new tank inhabitants.

I didn’t exactly need fish that were dependent on acidic water! How could I provide such conditions for these fish, so they would reproduce? My aquarium setup at the time was much smaller than it is today. The possibilities for water treatment were then quite rudimentary, and I searched for a long time for a way to provide them with optimal conditions.

In the meantime, I kept them temporarily in a tank that happened to be free. It measured 24 x 8 x 12 inches (60 x 20 x 30 cm) and was located just above the cool floor in my unheated basement. It was filled with normal city water, heated to about 75°F (24°C), and had a conductivity of 420 S/cm, a pH of 7, a total hardness of 12°dGH, and a KH of 8°dKH. This was not ideal for the successful propagation of these animals.

Apparently, the C. gracilis tolerated these conditions, but reproduction—as expected— was out of the question. In contrast to the experiences of other aquarists, in my experience the species is not totally inactive during the day and swims happily through the aquarium. Friends, even those who later received fry from me, reported that the animals are very shy and are active only at dusk. Even in my tank, they like to hide among the leaves (beech and Terminalia catappa—Indian Almond), but they come out to feed during the day and are extremely agile and fun to watch, especially when fed live brine shrimp.

I feed these animals exclusively with Artemia nauplii and a high-quality granulated food. Experiments with Tubifex and bloodworms have always led to losses.

Excellent hatch rate

For another Corydoras species, I created a mix consisting of two-thirds reverse osmosis water and one-third city water. Since I was out of tempered city water at the scheduled time for a water change for the C. gracilis, I used this mixture, and they seemed to enjoy it. It had a conductivity of 150 S/cm and a neutral pH; unfortunately, I did not measure the total and carbonate hardness. The temperatures in the basement were quite low at 64-72°F (18-22°C).

Since Hans had described their habitat as a small, highly shaded creek with a lot of leaves and branches, I added some beech and oak leaves and several driftwood pieces. The leaves and the wood turned the water brown and made it slightly acidic. Combined with the low temperature of the mixed water from the water change, I created exactly the right conditions for successful reproduction.

Much to my delight, a few days later I found about 40 eggs on a small Anubias. The fish had attached them only to the underside of the leaves, so it was very easy to put them into a small nursery trap. All attempts to raise the fry outside the parental tank failed. I was able to hatch the larvae, but then they died very quickly.

The larvae hatched after about four days and the hatching rate was very good. Two days after hatching, I began feeding exclusively with microworms. After two weeks, I added newly hatched Artemia nauplii.

After another two weeks in the nursery tank, the group was moved into the tank with the parents. At that time, the fry were about 0.2 inch (0.5 cm) long and no longer interesting to the parents as food. They quickly integrated into the existing group of adult animals and no longer needed special care. They were fed the same food as the parents, and they grew and thrived to adulthood without any further complications.

No more imports

Today, I take care of these animals in a 40-gallon (150-L) tank measuring 32 x 20 x 14 inches (80 x 50 x 36 cm). The husbandry conditions have not changed. My experience has shown that these animals are best reproduced during the period from November to March at a pH of 5. From late March to October, I switch to normal city water. During this time, no reproduction occurs.

Corydoras gracilis is a beautiful and uncomplicated fish that I have now successfully bred for eight generations. I still have a lot of fun with them. All of the existing animals in the trade probably go back to my original group, and I am quite proud because in nature the species is probably no longer commercially fished, since its collection area is gone. Thus, it is even more important to maintain them through breeding in the aquarium.

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