by Don Kinyon
Sometimes, through meticulous care and careful attention to the fishes’ diet, you can get a new or favorite fish to spawn in your aquarium. Other times, through inattention, lack of good care, and poor maintenance almost to the point of neglect, the fish spawn anyway.
Corydoras napoensis is a very attractive fish that certainly deserves the best of care. From the Rio Nanay, near Iquitos, Peru, comes this nicely patterned catfish. There are also populations in Ecuador in tributaries of the Rivers Aquarico and Napo, from which the name is taken. Nijssen and Isbrucker first described it in 1986.
My particular fish were wild caught in Peru by Julio Melgar on one of his collecting trips. The fish came to me unnamed, as I think he wanted to see if I could figure out what exactly they were for myself. There were later discussions over what the fish must be, and for a long time we didn’t agree on the species. I, armed with every Corydoras book printed in English, said the fish must be a nanus species. Julio, one the other hand, had a vastly superior knowledge of all things aquatic, the exposure to some of the best minds in the science and hobby of fish, and knew the pinpoint location of where the fish were collected. He argued that they must be of the species napoensis. I lost.
These fish had most physical traits in common with other napoensis: a short snout, fairly high dorsal (especially males) and a mottled gold and black color pattern, with a large black patch on the otherwise clear dorsal fin. The male will grow to be about two inches long, the female a little larger. As with most Corydoras, when viewed from the top or bottom, the female has a much more rounded body from the insertion of the pectoral fins to the anal fin. When the light is at the right angle, the gold in the body will show a violet iridescence. The difference in my fish is that the pectoral, ventral and anal fins are bright yellow, and the dorsal, caudal and adipose fins are a pale yellow.
When I received the group of fish, which turned out to be three pair, I set them up in their own 28-gallon tank, with soft, acidic water at about 74°. There was an outside filter and a power head in the tank to add oxygen and turbulence. They fed mostly on live foods: black worms, white worms, and chopped earthworms, along with frozen bloodworms and grated beef heart. They grew rapidly and the females swelled with eggs, and for a while it seemed that spawning was imminent. The fish would be particularly active after a water change, which they got weekly at about forty percent, but nothing more happened. I experimented with colder water, larger changes, letting more time go between changes, and the usual tricks, but none worked. Eventually I trained more attention on other fish and the napoensis fell to a lesser priority.
It must have been several months later that I once again noticed them. Not for themselves, but for the tank they were in. I returned from a trip to a distant fish store and, as is my habit, I came home with more fish than I had tanks for. A particularly nice pair of Apistogramma species needed a home, and one of the options was to put them in with some of my Corydoras catfish.
Just to make sure the change of conditions wouldn’t shock the cichlids too much, I checked the water they were in from the store: (7.0 pH) and the water in the Corydoras napoensis tank: (ouch, a little acidic: 3.9!). Now, I know better than to add my well water, which contains some strong buffers and is 7.4 pH, to a rain water tank that already has fish in it, especially one that’s gone acidic. Of course, for whatever reason, I did it anyway. In a matter of a few hours the pH rose from the low level it started at to a more reasonable 6.6. I don’t recommend this, and I’m sure most fish wouldn’t tolerate it well, but the little cats showed no outward signs of stress. They ate well that evening, and didn’t seem a bit bothered by the radical change of water conditions or the new tankmates.
The next morning when I checked on the fish to make sure that the Apistogramma made the transition all right, I was surprised to find seventy-odd small amber eggs on the glass. They were placed singly for the most part, and most were close to the water line of the front glass, with some on the body of the power head. A few spots on the glass showed that eggs had been removed, possibly by the parents, but more likely by the dwarf cichlids. I removed the eggs that were left to a three-gallon tank for hatching.
A small tank such as the three-gallon works well with most Corydoras eggs. I fill them about half way, add a little acriflavin to control fungus, add an air stone to keep the water circulating, and wait for them to hatch. It’s a good idea to check on the eggs at least once a day to remove any bad ones that start to grow fungus. When they hatch, instead of daily water changes, they get water additions to bring the water level up a little at a time. Once the level reaches the desired level, the air stone comes out, a sponge filter takes its place, and daily water changes of 3/4 gallon can start.
These eggs started to hatch in four days at 74°, and the last fry were out of their shells by day six. The fry look like an egg with tail, and don’t eat for another three to six days. Once the fry were eating, they grew rapidly. Micro worms are the basic diet for any Corydoras fry in my care, and they seem to do well with them. At two weeks the young were smaller versions of their parents and, at one month old and 3/8 of an inch, started to show some of the body markings of the adults.
At about a month, the young catfish were outgrowing their quarters, so a 15-gallon tank had to be filled with the same water to about the same level as the smaller tank. I set the three-gallon tank inside the larger one and let the stream from the outside filter run into the top of the smaller tank and overflow into the larger. This let the fry adapt to any differences that may occur in the new tank more slowly. After a few hours, I unceremoniously dumped and removed the smaller tank. The fry were unaffected. They now got 35 percent water changes twice weekly.
The roomier tank and frequent water changes did wonders for the growth of the fry. They ate more, were more active and seemed to get heavier and longer by the day. At seven weeks the young had the same mottled pattern as the parent fish, and were over 5/8 of an inch long. By now they were eating some fine flake foods, newly hatched brine shrimp, and decapsulated brine shrimp eggs along with the micro worms. This change of diet may also have added to their higher growth rate.
At ten weeks, I split the fry up into other tanks. It wasn’t so much that they had outgrown this one, but there was another bunch of Corydoras fry that needed it. A few went into the breeding group with the older fish, and some went to a larger growth tank with other catfish that would eventually be sold, auctioned or given away.
Corydoras napoensis is an undemanding fish to keep, breeds easily when the conditions are right (on purpose or accidentally), and a very attractive ornamental. Though it’s not very common in the hobby, it’s a fish that is worth seeking out.
This article first appeared in PVAS’s Delta Tale, Vol 33, # 2
© Potomac Valley Aquarium Society, Inc.