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Hey guys I have a breeding group of sterbai cories which breed on a regular basis but they only lay at most 50 or so eggs. I do not know if it is just that the female is older or is not being conditioned long enough. I may only have one female possibly two. What can I do to increase egg productivity. Also the eggs are all fertile. They are spawning in a ten gallon filtered by an HMF filter, kept at 78F, and I feed the fish plenty of protein rich foods. Any help would be great.

Have you tried raising the temperature? I'm trying to find the link but am experiencing memory lapse, that Ian had wrote that his spawn at 82F ... I do know mine prefer a temp of 80F to give me decent spawns.

I always kept and bred my C. sterbai between 82 and 86*F. Water chemistry wasn't very important within reason.
50 is a small spawn more typical of young adults. I don't think I ever bred any over 4 years old but only for a lack of trying.
Their fertility rate also improved with age. Although I have had them begin spawning at less than six months old they were most productive at two to four year old breeders were for me. Change a lot of water and feed them a lot of live Black worms and/or cultured White or Grindal worms.
Two reverse trios yielded about 1000 salable juveniles in less than one year for me.
I quit after that because it was difficult to find enough buyers and their prices dropped from about US$15 retail when I bought my first specimens to about $5 by the time I needed to sell them. I ended up selling the majority of those I raised for only $2.00 wholesale.
There was no profit in raising them once prices plunged.
Besides, they are difficult to ship due to their well documented tendency to exude toxic substances when they are disturbed then confined with large numbers per bag. Even relatively few adults in large and uncrowded bags can be difficult.

I breed mine in a 15 gallon, and I have a larger group of 8 fish. I breed them at 79 deg F, and they lay between 300 and 400 eggs over a period of 24 to 36 hours. I have found if I disturb them by collecting the eggs mid spawn they sometimes stop. I have also watched them eating their own eggs. I make sure there are no other fish in the tank and watch out for snails too. I find that while the common pond/bladder snails will demolish cory eggs very quickly, the ramshorn snails will occasionally eat them too. My C. sterbai only breed when they are fed tons of blackworms. Even if I cut down a bit on the worms to only once a week they stop breeding. If I feed them lots of worms and do a 50% water change every week they will spawn at least 2 times per month. Out of the 300 plus eggs I get each time I only ever get about 40 to 50 fry. I think this may be because I have more females than males in the group and the large bulk of the eggs never get fertilized. My females are big at about 70 mm or 2.8 inches, and the males are only about 5 mm smaller. I've tried spawning mops in the tank, but I find they seem to prefer to lay them on the glass so now I don't use them. I would not say I've perfected breeding C. sterbai yet, but I hope what I've done so far helps!

@apistomaster - I'm finding I can't produce enough of these guys to satisfy demand around here! I won't ship them because of the toxin release, but I'm having no trouble selling them locally at more than $5 a fish. Sorry to hear you had such trouble selling yours, seems like they should've been more profitable.

Cheers,

Rob

I live in rural eastern Washington state so there are relatively few shops and many are small.
Furthermore, many of these shops tend to buy from regional distributors who actually make delivery rounds every 2 or 3 weeks and the shops just replace what they have sold since their last deliveries. None buy most of their fish regularly in 100 to box lots. Selling to them in 12 to 25 lots at a time didn't make a quick dent in my accumulated inventory in the approximately year I was raising them but eventually I did sell them all.
I was working with my C. sterbai at the beginning stages of my fancy pleco breeding projects which eventually were much more profitable so my Corydoras weren't very important to me. I did enjoy learning more about them. I was soon producing and selling Peckoltia compta in the hundreds for many years at at least 6/$240.
I also had some problems with what I considered low fertility such as you described above but that did improve for me as my breeders grew older.
I also noted considerable egg cannibalism as you reported.
My breeding group sizes varied between 2 to 3 reverse trios and I used 20 Longs.
I also had snails present but mainly the Malayan burrowing snails(MTS. They did not seem to predate upon viable eggs to a noticeable extent.
I also used methylene blue to try to reduce losses to fungus during egg incubation. I do believe that C. sterbai should be kept for breeding in warmer water. My aquariums get very warm in the summer. It isn't unusual for higher tanks to reach 88*F. This is fine for the plecos and Discus I specialized in.
My favorite Corys are C. hastatus and the only Cory I continued to keep a continuous colony going over the years.
I no longer sell those because my health has declined enough to force me to cut way back on all my fish projects over these last 3 years.