Corydoras sterbai

These fish are found in the Upper Rio Guaporé, Brazil and were found in 1960. They prefer water values of 6.0-7.0 pH and 6º dGH. The best water temperature is around 75-79º F (24-26º C).

In February of 1997 I went to my local pet store, Capitol Aquarium located in Sacramento, to look at their rows and rows of tanks to see if there were any fish I couldn’t live without.

While walking along a back wall containing three rows of tanks, I noticed one tank in the top row to my right in particular. It had four Corydoras catfish in it that were approximately 2 ½" in length. They were tinted a light orange on their body with numerous, white on black dots, throughout the fishes body, including the dorsal and tail. In some parts of the fish the dots were so close together it appeared they were lines instead of rows of dots. Their pectoral spines are a deep orange. and are the same in both sexes. A very magnificent fish to behold. On the tank, I checked to see what name the store had given this particular fish. The name given this particular cory was Corydoras sterbai. They had the right name.

These fish have constantly been confused with Corydoras heraldschultzi because they do look very simular. Upon close examination one can tell the two species apart. The Corydoras sterbai looks like his head markings are white on a dark background where as the Corydoras heraldschultzi is just the opposite with the head looking like it has dark markings on a white background.

Now this may seem strange to some people but this is like a hobby to me. I enjoy going into retail stores to find out if any of the corys are misnamed. My fiancé has also picked up the habit of wanting to check the names written on the tank with the actual species contained in the tank. He does not try to identify them, instead he will call me over to the tank and ask me what species of cory is in the tank. When I operated my own retail store in Corning, CA. in 1988, I got a reputation from a few of the stores I frequented in Red Bluff and Chico for knowing some of the most popular species. They would ask me to come in and verify they had the correct species name of the fish listed on their tanks. It surprised me how thoughtful about having the correct names the managers were and they would then change the names on the tanks if I suggested they were misidentified.

This is not the fault of the retailer or the wholesaler. The problem, explained to me by a wholesaler, was that the name that comes with the fish when they purchase them is what goes on the tanks and on their price lists. They don’t have the time to check every species of fish that comes in with the available books they have for sale. Most fish, (99%) of all fish at a wholesaler are gone within a week.

Back to the story at hand. As I stood in front of this tank I noticed the group had been spawning and laying their eggs everywhere on the glass sides. The price was $29.95 each. I thought to myself that $120 for four fish was too much, but told my fiancé that we could not pass up this opportunity. I also knew what this species was worth. The fish were already spawning and I would not have to wait three to four months, or longer, for them to mature enough so I could identify the males and females. We talked to one of the employees and we took the four fish home INCLUDING all the eggs that the four fish had placed on the glass sides of the tank.

Normally when I purchase corys for breeders, I buy at least 10 young fish at about an inch in length to guarantee that I will get at least a trio. Two males and one female.

It turned out that there were 3 females and one male. Not bad but, usually with corys I would prefer more males to females. It works out nicely though. This group is apparently working because so far every egg I collect is fertile. The sterbai female lays eggs that measure 2.08 mm in diameter and are large (for a cory), the female sterbai does not lay a large quantity of eggs.

The easiest way to sex your corys is to view them from above. In some cases one can tell by the height of the dorsal fin of the male when viewed from the side. The female is on the right and is widest in the ‘belly’ region behind the pectoral fins. The male is much slimmer and is widest at the pectoral fins. Another way of identifying sexes is to turn the fish upside down and look at their vents. The female has a round vent whilte the male is more like a slit. The one drawback on this method is that in immature corys this is not pronounced enough to be reliable. A female will actually look like a male or vice-versa.

The sterbai spawn in the normal cory fashion. The ‘T-Position’. This is described as the female putting her nose to the side of the male who then curves his body around her head and the male clasps her barbels with his pectoral fins. How exactly the eggs are fertilized, no one really knows. It has been a debate for years. After a few seconds, and shaking from the male, the female can be seen holding one or more eggs in her ‘basket’. This basket is made when the female clasps her ventral fins together while she is in the T-position. The female leans slightly on her side for one to two minutes and then regains her composure and then begins looking for a place to place her eggs. This in itself is interesting to watch. The female can be seen going all over the tank glass rubbing her barbels as if trying to find the perfect place and then cleans the spot she has chosen. Once she has found the ‘right’ spot she will press her belly to the glass as she opens her ventral fins and presses the eggs onto the glass. The eggs are very sticky and are clear. The eggs of the sterbai have a light orange tint to them and so do the fry after hatching. As the fry develop the eggs get darker. Non fertile eggs turn white. Two days after being laid one can see the starting of the spine and the black dots for the eyes. One can also see the heart beating if the angle is just right. To see the heart beating I use my Minolta Maxxum 7000i camera that has a 50 mm Macro lens attached with 1 x, 2 x, and 4 x attachment magnifying lenses.

What happened to those eggs I collected at the store you may ask? I put them in an ‘egg tumbler’ that was originally designed for hatching mouth brooding cichlid eggs. I had to modify the tube a bit for the cory eggs by purchasing a six foot length of clear plastic tubing that was 2 ½" in diameter and having it cut to 8" lengths. (This length is long enough for a 10 gallon tank.) I put a hole in the side about an inch from the top of the tube with a very hot nail. This hole is made for the suction holders we bought specifically for this purpose. The tube had to be wider than the original design because the cory egg quantity is significantly larger then the spawns of mouth brooding cichlids. Another change I had to make was the material I used to cover the bottom of the tube. The cory eggs are smaller than those of mouth brooder eggs. I needed a finer mesh net to cover the bottom of the tube. With the old design, the eggs would be about 1" thick and the eggs would have troubles hatching from overcrowding and not being able to get the circulation they needed for hatching. With the larger tubes, the eggs are one layer and at most two layers high. (One layer was approximately 200 cory eggs.) The tube was suctioned to the inside top part of a 10 gallon tank that we had put in our bathroom on the counter. Why in the bathroom? We had no more room in the bedroom/fish room for any more tanks! I put a Hydro-Sponge #1 filter in the tank and nothing else. I had previously left out the filter on a spawn of C. paleatus eggs assuming there was not going to be much ammonia etc. from the eggs. I found that I needed to have a filter in the tank with the hatching tube otherwise the tube itself acted like a filter and would suck all the debris (dust, etc. from the air that is in the tank) through the bottom of the tube which was covered with a fine mesh. While doing this the debris that collected would actually kill the eggs because not only was there bacteria building up under, in, and above the mesh and killing eggs, it was also cutting off the circulation the eggs required to hatch.

The eggs hatched on March 13th. There were 25 fry. Subsequent spawns revealed the eggs hatched after five days at 74°F. I didn’t know the exact days from the eggs that I collected in the pet store because I didn’t know when the eggs had been laid. After another six days the fry were free swimming. I started them on newly hatched brine shrimp.

It is now December of 1997 and I decided to try something new as a food for the fry a little over a month ago. My fiance had heard David Kawahigashi speak at the Marine Aquarist Roundtable of Sacramento at a meeting earlier in the year talking about deencapsulated shrimp cysts. (We also heard him speak again at the NCKC - Northern California Killifish Club on Feb. 7th, 1998.) These were low grade cysts and were not intended to be hatched. What we liked most about them especially for me, was I would not have to hatch anymore brine shrimp.

So I thought. I started a new spawn of free swimming angelfish and sterbai fry out on the decap cysts instead of the live brine. These are a good food source for fry because they are 100% protein because the shrimp is not absorbing the yolk sac themselves. I did lose some fry. Since the corys mainly find their food by smell, I still needed to start them on newly hatched brine for a couple days so they would get used to the smell. Then I would be able to switch them to the decap cysts. The angels were swimming and faired better than the corys. I did find out that I would have to start the sterbai on the live brine shrimp first. I did start another batch of angelfish fry on the decap cysts. They are taking a little longer to adjust. I definitely recommend starting any fry, large enough for newly hatched brine shrimp, on the live brine for two to three days first and then switching to the decap cysts. The batch of C. sterbai I started on the decapsulated cysts from the beginning did not all survive. I started with 116 fry. This is when I realized the fry needed to be started on the live baby brine first. I had seven fry survive. At one month the fry were a little over a 1/2"! Not bad growth.

I breed my four sterbai in a 10 gallon tank with just a sponge filter. Either a Hydro-Sponge or one that attaches to the tank glass. I feed the adult sterbai live tubifex worms. There is a lot of controversy about the benefits versus the drawbacks of live tubifex and feeding them to ornamental tropical fish. I will not go into that debate here though. I do know that I have better results with my breeders and their offspring when I feed them the live tubifex worms. After the breeders spawn, I scrape the eggs off the glass sides of the aquarium and place the eggs in either a net or in an ‘egg tumbler’ that I have hanging in a new setup tank. I also place a Hydro-Sponge #1 filter in the tank. The net that would contain the eggs would be placed near the output of the filter but never in the direct out-flow.

One question I am always asked concerning my hatching method is "What type of anti-fungicide do I use?". The answer is easy, none. When I first started breeding corys in 1987 I tried the common chemicals like everyone else. I tried the Methylene Blue on some C. paleatus and C. aeneus (albino form). I did not like the results. When the paleatus were a week old, they were large enough for me to see they were ALL deformed. Not a good sign. With the albino aeneus, the fry died within a couple of minutes after hatching. This is when I started using nets to hatch the eggs. I knew I didn’t want the eggs to just sit on the bottom of the tank because all the dust etc. that is in the water column would also settle on the bottom of the tank as well as on any eggs that were resting on the bottom. In the nets the eggs were still able to get the circulation they needed and all the dust particles and other minute things in the water column would fall to the bottom of the tank instead of on the eggs. How do I control fungus? I check the eggs everyday and take out any eggs that have turned white. With the sterbai there is rarely a time when I need to remove dead eggs.

References: Baensch Aquarium Atlas Vol 2, by Rüdiger Riehl, Hans A. Baensch, 1993, Microcosm Ltd.