What the heck is a CW number?
by Rob McLure

 hile many of you may have heard of Plecos being given L numbers, I wanted to take an opportunity to tell you a little bit about C numbers and CW numbers. First, regarding the photo. I have chosen this specific photo for a reason. At first glance these fish seem pretty similar right? You might even be thinking, that’s just 2 examples of the same fish! Don’t feel bad when I tell you – no, you are wrong! Even the experts in the Corydoras hobby felt that these two fish were the same species for a long, long time.



Corydoras parallelus (C002) & (CW127)

Corydoras parallelus (C002) & (CW127)


Let’s start with the little fella on the left (yes, it’s a male). This fish entered the hobby in the early 1990s. Hobbyists knew a little about it, such as that it was imported from the Rio Negro, a blackwater river which flows into the Amazon and touches the Northwestern South American nations of Colombia and Venezuela before draining into the Amazon near the city of Manaus, in Northwestern Brazil. It is a “Northern” tributary to the Amazon. When this fish entered the hobby it was not described – in other words, it did not have a scientific name (nor did it have a common name for those that are hung up on that).

As most experienced hobbyists prefer to refer to fish by their scientific name, and there was really nothing like it, what were we going to call this fish? Something that everyone, regardless of region, language, etc. could agree on. Enter Hans Georg Evers, at that time already an established hobbyist, adventurer/fish collector, and author for the German Aquarium Magazine “DATZ”. Hans suggested using DATZ as a platform, to create a system of “C-numbers” like there were “L-numbers” for the plecos, and the C-Number system was born.

Corydoras parallelus, at that time briefly known as “C002” was one of the first ever C-number fish presented in the magazine by Hans. In this case, it did not last for very long. Later that very year (1993) C002 was described in the Tropical Fish Hobbyist Magazine, by Dr. Warren Burgess. What happened? Did C002 go away when this fish was described? Would it be re-issued? No, even though C002 was described as Corydoras parallelus, the number stuck with the fish, and it can now be referred to as either it’s C-number or name, but most people call it by the scientific name, Corydoras parallelus.

The C-number system was used from 1993 through 2009 and 159 “C-number” catfish were “described” in brief detail, all with a photograph in the DATZ magazine. Notice I said “catfish” and not “Corydoras”, this is because several of the C-numbers were Scleromystax or Aspidoras – not just Corydoras. Many of the C-numbers have since been described by science, and we just typically don’t use them at that point. C005 is Corydoras pantanalensis, C064 is Corydoras tukano, C111 is Corydoras nijsenni – to name a few. The vast majority have not yet been described, and the C-number is still the best way to refer to that particular fish, that anyone, from anywhere, will know what you are talking about. While the C-number articles are written completely in German and old copies of DATZ magazine are not exactly easy to get a hold of, if you are interested in looking up some C-numbers websites like Corydorasworld.com, Scotcat.com and Planetcatfish.com have databases containing all the C-numbers, (and CW-numbers) most with images and information about the fish themselves.

Please note I mentioned that C-numbers “were” used until 2009, so what happened. In 2005 Hans Georg Evers founded Amazonas Magazine and generally moved away from DATZ. The folks that ran DATZ magazine attempted to keep the C-number system going for a few more years, but I’m guessing, eventually, without the expertise that Hans provided, they decided to discontinue issuing new C-numbers. I don’t know the entire story, but what’s important here is that we did have a system, but suddenly it was gone. Given the vacuum that was left, Ian Fuller, in combination with Hans Georg Evers decided to form a new system, the same basic principles applied, but they could not use “C-numbers” as that was considered the property of DATZ magazine, so they had to start fresh, and began a new numbering system- with all new fish – starting from number 1 (CW001). They called this the CW system, after Ian’s website Corydoras World. This new CW system took off like a rocket, and by the time Ian and Hans book “Identifying Corydoradinae Catfish Supplement 1” was released in 2011 there were already 60 new CW numbers issued in addition to the previously existing 159 C-numbers. Recently the number of CW numbers has passed the total of C numbers and as of this writing there are 165 CW numbered catfish!.

Back to looking at the photograph, now that you know a little more, the fish on the right is CW127. How did that come to be? For years this fish came in almost exclusively in the Asian markets as often happens with new or rare species. Tropical fish prices in Japan, Korea, China, Singapore and other Asian markets are often extreme. To give an example, when Corydoras geoffroy re-entered the market after decades of absence, a few years ago, many of the first shipments went to Asia, why you ask? Well when this was going on, I browsed the internet and found an online store in Japan selling Corydoras geoffroy, a single male was priced at $1800.00! So collectors and exporters often offer new or rare fish to the Asian markets first, as they tend to be able to get a lot more money. To get back on topic, the fish in my photo on the right came into the Asian markets and they often posted photos of this one calling it “Super parallelus.” Now this trick has been tried before… A lot of people know about Corydoras schwartzi, which, at least in my local fish shops, is a $5 to $7 fish that comes in seasonally, and usually in pretty big numbers. There is a close relative to schwartzi, that is much bigger in size, brighter in coloration, and often has a huge dorsal spike, it also comes in far less frequently. That fish, known in the hobby as CW028, was given a nickname “Super schwartzi” and as a result commanded a much higher dollar amount – seeing CW028 for $25, $30 or even higher prices is very common. Knowing that putting the word “super” in front of a name commanded a higher price, this has been tried with lots of species. Sometimes, it’s a different fish, but in many cases “Super eques” or “Super pulcher” is just someone trying to make a little extra money. When hearing about “Super parallelus” aquarists in the west doubted that “Super parallelus” was anything more than just a slightly larger, overly priced Corydoras parallelus. Another example of the problems that “common names” can cause…

Back in 2015 Ted Judy was importing fish for sale on his website “Tedsfishroom.com”. Ted let me know he was going to import some Corydoras parallelus and I would be lying if I said I was “only mildly interested.” The day came and Ted let me know they had arrived. Very excited, I got over to his warehouse in Stoughton, WI and immediately noticed that something wasn’t quite right. I already had a few parallelus males received from a friend, and seeing these fish for the first time I noticed 2 things. For one, these fish did not look quite the same as my parallelus, the stripes were broader, the fish were darker colored as a whole, and they were much larger than my adult parallelus, which were pretty good sized! The second thing I noticed, was that they came in with some longer snouted Corydoras, that were definitely not parallelus, and looked a lot like Corydoras bifasciatus. I made a deal with Ted and was able to get 8 of the “parallelus” and the 2 longer snouted fish they came in with. After getting them home I took photos and shared them with a lot of friends. Ian Fuller and I discussed the photos and he agreed that the one of the long snouted by-catch was definitely Corydoras bifasciatus, but the others he thought were likely parallelus. I started doing some research and found out that Corydoras bifasciatus came from the Rio Tapajos, a tributary to the Amazon and in Central Brazil, at least 1000 miles away from the location of the Rio Negro where parallelus are found. Finding out more from Ted I also spoke to the exporter, and he told me that all these fish did indeed come from the Rio Tapajos.

The Rio Tapajos is a “Southern”tributary to the Amazon. I contacted another friend, Mike Downey who had also bought fish from Ted and said Mike! Get those guys out of your parallelus tank! I don’t think they are parallelus, and Mike did. A short while later Mike sent me a message, he had gone out of town for weeks, and when he came back, he found a few fry in the tank of these new fish we got from Ted. Lucky guy! I thought, but my luck was soon to follow as I also discovered my group laying eggs, relatively small eggs – nothing like the very large round eggs that parallelus produce. My fish seemed to eat the eggs almost as soon as they were laid, so I was only able to collect eggs for and raise 8 tiny fry. I went back to Ian, and with all this information, and some input from other aquarists around the world Ian did agree, these are most likely not Corydoras parallelus, and are probably something new. He gave them the new code CW127.

I maintain my group of CW127 to this day, and have very infrequently, convinced them to spawn. While the Rio Negro is blackwater (looks brown or tea-colored) the Rio Tapajos is clear, and that is just what I have seen, that the CW127 spawn best when I have really paid extra attention to the tank and the water is extra clean and sparkling clear. I had always wanted to try to really figure this species out or “crack” it and produce a lot of them, but since that time they have been introduced into Indonesian fish farms and are starting to be mass produced. While I enjoy them, it doesn’t make a lot of sense to try to produce a ton of fry when a fish is being “farm-bred”.

In summary, I hope you have a better understanding of what a C-number is, what a CW-number is, and a little bit of insight into what goes into making a new CW number. I personally find these systems extremely helpful, and while every C or CW number may not eventually be made into a scientifically described species, I feel that they are a great place holder, and a perfect way to discuss fish that have not been given a name with other aquarists from all over the planet. I hope the CW number system will continue indefinitely, since new Corydoras and their relatives are being found all the time. I also hope you’ve enjoyed reading, and maybe learning a little more about them.

This article was first pulished for the Milwaukee Aquarium Society July 2020


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