Corydoras C123, or the "Yellow Cat"

by Don Kinyon

This is a very distinctive Corydoras catfish native to the Rio Nanay in Peru. What makes it distinctive is the bright yellow coloration of the fins, particularly in the males, almost never seen in Corydoras. Otherwise, they resemble most of the elegans-type Corydoras; having a dark brown body with silvery white markings. The pattern is mottled at the head and then forms two more-or-less stripes on the back of the body to the tail. The dorsal fin is yellow with horizontal dark bands as is the tail, the caudal fin having less dark coloration. The rest of the fins are yellow as well. The males get around two inches in length while the females grow larger by half an inch and are much heavier-bodied.

I was lucky enough to find a group of these fish at an aquarium society auction. I’d never seen this species available before and won the bidding (I would have gone a lot higher!). Later I was able to talk to the seller and found that the fish were first generation from wild-caught and learned the method he used to trigger the spawn. A month later, I found that a collector had brought a small group of wild-caught fish back from Peru and had them for sale. I bought this group as well and added it to the few that I had. This left me with four males and five females; not perfect for Corydoras breeding but good enough.

The group already seemed to be mature enough to set up as breeders, so they went into a 30 gallon long aquarium as a breeding tank. There were two air-driven sponge filters; one at each end, and a medium-sized power head in the right front corner with it’s flow directed down the front glass and a small sponge covering its intake. The floor of the tank was covered with a thin layer of river sand and there were a few stones scattered throughout the tank bottom. The only other extra piece in the breeding tank was a single large yarn mop.

The hobbyist that had spawned and raised the first fish of my group told me that through circumstances beyond his control, the fish had to go through an “artificial dry season” for a while with not much food or fresh water. When things were back to normal he started water changes with rain water, which triggered the fish to spawn. When my breeders had shown no interest in spawning for a few weeks even with lots of live food and two or three times a week water changes, I decided to try and duplicate the circumstances with which the original breeder had had such success.

I drained about half the water from the tank, covered it with some towels and put a sticky note on the top with the date that I’d done it. I waited. Waited some more. The fish in the tank were not getting any water changes and not much to eat. I waited until I could no longer stand it, which turned out to be 18 days. I’d found my limit: I can only abuse fish for two and one-half weeks. Once the cover was off, the tank was drained further, to about two inches from the bottom and filled with cooler rain water. The breeders were fed well from that point on with mostly live and frozen foods, supplemented with Repashy jello and freeze-dried tubifex. The females grew rotund and the males grew much more active, chasing the females around the tank. This lasted two or three days, then: nothing. Two more weeks went by and still nothing. Four weeks, then five, then six went by and I’d about given up.

Through some fish trading I obtained five more fish from Matt Chambers, the hobbyist that had originally spawned the fish. These were younger and not old enough to breed yet, but I figured that it certainly wouldn’t hurt to mix up the tank a little since nothing else seemed to be working. I got the five healthy young fish and put them with the group. Eight days later there were eggs on the front glass near the outlet of the powerhead. Not a great amount, around 50, but at least there were some eggs. I’m not sure if adding the young fish had anything to do with the spawn or not, but it’s the only thing that changed.

By shutting off the power to the powerhead and carefully sliding a razor blade under the very adhesive eggs, they could be removed without damage. There is always a turkey baster at the ready in case an egg or two fall from the blade. The eggs were dropped into a 5 ½ gallon tank with water from the breeding tank and some alder cones, sponge filter, and a fine sand layer covering the bottom glass. There are always a few oak leaves in my fry tanks to give the young fish cover and more surface area to scavenge for micro foods. Within a day, most of the eggs were turning white and hairy, and in two days the vast majority had gone bad. “Spotlighting” the fish with a flashlight after the lights had gone out for the evening showed some movement under the leaves, so the tank was left as-is for a few more days. It turned out that only a very few fry hatched and survived the first spawning.

I was contemplating putting the fish through another “artificial dry season” when it became necessary for me to have shoulder surgery, leaving the fish to fend for themselves a few days. Even once on my feet, doing water changes and moving fish around was not in the cards, but I did manage to feed them well. With so much time on my hands, wandering the fish room became a regular routine; otherwise, I may not have noticed the eggs in the C123 breeding tank hidden in all four corners near the water line. The placement wasn’t unusual for Corydoras, but the formation was. Each corner had a ball of eggs placed almost where the two plates of glass came together and almost to the water line. The largest ball was over 3/8” and the smallest about ¼”. There were a few scattered eggs near the balls, but none in the mops or sand to be found. The only other eggs found were a few on the motor section of the powerhead.

These eggs were all removed much the same way as the first group, although working one-handed made it painfully slow work. I separated the eggs by hand as much as I could, so that there weren’t any large groups stuck together. Most of the groups were three or four eggs by the time they went into the hatching tank. The hatching/rearing tank was a 7 gallon set up as the first, with a sponge filter, oak leaves, fine sand bottom and an Alder cone. Two days later, just as the first of the eggs were hatching, the fish spawned again. This time the eggs were in only two of the corners, but some were in the mop and along the bottom of the front glass. The mop had more eggs in it than I wanted to pick out, so I dumped it into the hatching tank and replaced it in the breeding tank with a fresh one. The rest of the eggs were separated and joined the first group and the mop in the hatching tank.

In one more day all the eggs that were going to hatch from the first group had hatched and three days later the second group had hatched out. There was really no way to tell how many were present at this point. The fry at hatching are very small and need micro foods. The smallest of the Golden Pearls brand foods will work, as well as pulverized and soaked flake food. Within a few days, a week at the most, the young fish were able to take micro worms and then decapsulated brine shrimp eggs two weeks later. At this point the young fish were 5/16” to 3/8” long and very active: they no longer hid under leaves and the edges of stones during daylight hours but were out scavenging for food most of the time. Their coloration and body shape was nothing like the adult fish: they looked more like tiny zebra-striped sharks. In order to keep the pressure changes to a minimum on the fish’s delicate air bladders, small water changes were done two to three times a day.

At this writing the young C123 “Yellowcats” are two months old and growing fairly quickly. They’re around an inch long and constantly searching for food. The air bladders of the youngsters will be developed enough at this point to do larger water changes without worry, and they will soon be placed in a larger tank to grow them out.

This is an unusual Corydoras that is a fine addition to a community tank, or a great display in a one-species tank. They may pose more of a challenge to keep and breed than many Corydoras catfish, but in this hobbyist’s opinion they are well worth it.