By Don Kinyon
Corydoras identification has never been my strong suit. This is the cause of much confusion on my part, and on the part of those who sometimes take what I say for more than an educated guess. I'm thinking that this is one of the occasions that I got it wrong, and owe an apology to anyone who may have acquired these fish (or bad advice). That being said, this is a very cool little Corydoras and a great addition to anyone's collection.
I found a tank full of colorful young catfish marked as "Corydoras Sp. 'san juan'" at a store specializing in tropical fish. The store owner always stocks unusual fish and is knowledgeable about many species. He said that in his experience, many varieties are imported as "san juan" because the importers or wholesalers just don't know what else to call them, and these particular fish were Corydoras bilineatus. I'd never kept C. bilineatus before, so I bought all of them. Later conversations with hobbyists led me to send pictures of my fish to Corydoras people, who are far better at ID than I, to beg their opinions. Most all agreed that the fish I had were C. napoensis, not C. bilineatus.
The fish in question is an "elegans- type" Corydoras and is black with white/silver markings. The markings start out mottled on the head and then more-or-less form two stripes down the posterior of the body to the tail. The tail itself is clear and has meandering vertical black stripes. Most of the fish have a black dorsal spot. One of the cool things about this particular Cory is the prominent "headlight." When seen from above, even in low light, there is a spot at the top of the head just in front of the dorsal fin that reflects a bright amber/orange. A group swimming together is really something to see.
It's always best to know what conditions your new fish is native to in the wild so you can do your best to duplicate those conditions in the home aquarium. If you don't know what species it is, it makes it all the more difficult. As luck had it, these two varieties share very similar conditions, though their habitats are not close to each other geographically.
C. napoensis is found in the upper Amazon River valley in eastern Ecuador and Peru. The waters are fairly soft and neutral to slightly acidic and tend to be around 70°F average temperature. Due to weather conditions and seasonal changes, the water parameters in which these fish live can vary somewhat on a daily basis and much more so over the course of the year.
The water in their 20 gallon long tank was as close to nature as I could make it. A mix of well and rain water was used to bring the pH to 6.5 and the TDS to 100 PPM. There was a thin layer of fine sand on the bottom of the tank, a yarn mop and some bog wood that the fish would dart underneath when frightened. Two air-driven sponge filters were the only filtration and there were no added light or heat sources. The air stream to the filters was kept very strong, causing some current in the tank and it would wash the sand out of the corners. The catfish would almost always be seen in the center of the tank, digging through the sand with their snouts and rarely seen on the bare glass. This could be because the food would wash to the center with the sand, but I believe the fish rather enjoy digging around in the sand as well.
My fish were at first too young to accurately judge the sexes, but in a few months it was clear that I had a good mix: eight males and five females. They are very active and ate anything offered. A mix of flake, freeze-dried, frozen, and live foods got them into condition very well. The females were soon rather large and the males were becoming more active and chasing the females, especially in the morning hours.
Performing a large water change with cool water coinciding with a low pressure system passing through the area is something most every Cory keeper has done to trigger a spawn. In this case, worked like a charm. A fall thunderstorm was passing through on Friday night, so the breeding tank got its weekly water change a little ahead of schedule. In the early evening the fish got an 80% water change using cool rain water: about 65°F. At 10:30 on Saturday morning the fish started to spawn and kept it up for over two hours. When they were done, there were around 200 eggs, mostly on the glass near the water line, but some on the lower glass, mop, and even the filter tubes.
At this point, with the number and placement of the eggs, it was easier to move the adult fish than try to remove the eggs without destroying a good portion of them. The adults went into another tank and some Acriflavine was added to the breeding/rearing tank water to try and cut down on fungus spreading. A good number of the eggs were infertile and turned white in the first 24 hours, but about half stayed a translucent amber color and in three days, they started to hatch. The fry were fairly large for Corydoras and in three more days they were out in the sand looking for food, which was either Golden Pearls, micro worms, or decapsulated brine shrimp eggs, fed alternately, twice daily. To prevent damage to the young fish's developing air bladders I always reduce the amount of water changed at one time and increase the frequency. A 15% change every day kept the water fresh and did no harm to the youngsters.
Once the brood was five weeks old and between 3/8" and 1/2" in length, they could be fed the same foods as the adults, thought more finely chopped or ground and they grew even more quickly. By now they were a smaller version of the parent fish and acting very Cory-like.
At this writing, the young fish have been moved to a much larger tank and are growing like crazy. The original parents are back into the breeding tank and have spawned several more times. With no room to move the eggs or parents, parents and young were left together and no great amount of predation was evident. The adult fish and batches of fry are living together in harmony, although they do compete for food. Many of the first brood have been traded or sold to other hobbyists and are hopefully thriving and multiplying in their care.
This is a great little Corydoras to keep, no matter what the name.
© Potomac Valley Aquarium Society, Inc.