By Don Kinyon
It seems that almost every day there are new additions to the group of Callichthyidae catfish we keep in our home aquariums. Most are fairly plain and unspectacular, some are very unusual, and the rest fall in the area between. Corydoras knaacki (pronounced “knock-eye,” I’m told) is one that falls in the more colorful and desirable category. It’s been in the hobby for a while; first under the name “Morse Code Cory,” then given the designation CW032 by Ian Fuller, and finally described as C. knaacki in 2016 by Tencatt & Evers. It’s found in the drainage basin of the rio Madre de Dios in Peru in soft, tannin-rich fairly acidic waters.
The closest common relative and cousin in appearance is C. bondi. This fish is close in size and coloration to the C. bondi, being a mid-sized Corydoras and a base color of silver/bronze with black markings. The markings are in rows of irregular dots and dashes, giving the fish its nick name. The dorsal and caudal fins have the same markings, the ones on the tail arcing away from the body. When the light is just right, the body of the fish will show an iridescent green.
I was lucky enough to find a bag of juvenile C. knaacki at a local club’s fish auction. The five youngsters were too immature for me to be sure of the sexes, but as they grew, I found I had two females and three males; perfect! They were housed in a 15 gallon long tank by themselves. Two air-driven sponge filters provided all the filtration, aeration, and water movement that was needed and two yarn mops were all the “furniture” in the tank. There was a thin layer of fine brown river sand coating the bottom glass. Water was kept at room temperature: hovering around 72° F and was a 50/50 mix of well water and rain water, bringing the TDS to 125 PPM and the pH to 6.5. Water changes were done weekly at around 50% using the same mix.
After keeping the fish about six months, I found about 80 free-swimming fry under the mops as I was starting a water change. Instead of disturbing them any further, I removed the adult fish and put them in a tank of other Corys. The youngsters looked to be a week or so old, so I believe this particular Corydoras isn’t predacious to eggs and fry. In fact, later spawns were left in the tank with the adults and there were no fry feasts.
I added a few oak leaves into the tank at that time to give the fry more places to hide and provide more surfaces for them to hunt for food. They were fed twice daily, rotating between Golden Pearls, micro worms and decapsulated brine shrimp eggs. Water changes were downsized to about 10 to 15 percent at a time, but done three times a week. Avoiding the large pressure changes will, in theory, decrease the chances of harming the young fish’s more delicate air bladders.
The young fish grew at a good pace with this care and in six weeks were smaller versions of the adults. I then put the adults back into the tank and they spawned the next morning. This time everybody stayed in the tank and all was well.
At this writing the first spawn is not quite a year old and starting to exhibit spawning behavior. There are subsequent broods in the tank as well, and many have been distributed to other hobbyists. This Corydoras is attractive, active very easy to keep and relatively easy to spawn and rear. I can recommend it to anyone that wants to get their feet wet with Callichthyidae.
If you haven’t been to a fish auction and there’s a group that does auctions within your driving distance: shame on you! It’s a great way to find fish you don’t normally see in pet shops, and most times they are cheaper and healthier than pet shop stock.
© Potomac Valley Aquarium Society, Inc.