Corydora Breeding Help - What am I doing wrong?

I have one female and three male Peppered Corydoras that have been laying eggs like crazy, but I've had very inconsistent success. I always remove the eggs by rolling them off the glass with my finger so they stick to my finger, and then rolling them onto the side of another container.
The first batch I collected had been laid 8-12 hours before. About half were fertilized and about half of those hatched, giving me four fry. The second batch was similar with about 70% fertilized and and all but one hatching, giving me 6 fry. This gave me some confidence.
But the next time, I saw the cories breeding in the morning and began pulling the eggs off the glass as soon as they were laid. I collected about 110 eggs. All but 5 got a white yolk within 24 hours and the last 5 I finally tossed after seeing no change 8 days after they were laid. I thought perhaps they got temperature shocked because I was putting them in a smaller container that, though it started out the same temperature as the tank, may have cooled over the hour or two that they were laying eggs.
It was at this point that I got a breeder box for the 6 fry I still had (4 of the smaller ones had died while my sister was caring for them, perhaps due to bad food). The next batch of eggs was small, only 21 eggs. I put these in the breeder box with the older fish. They were originally stuck to the side of the box but the older fish knocked them to the bottom where they constantly moved them around. 19 were fertilized. These eggs took a four hour trip in the car in the breeder box with no heater, and I lost only one. The remaining eggs are hatching today.
Yesterday, I collected 103 eggs in exactly the same way as last time and this morning all but 3 have a white yolk. The older catfish only knocked ~20 eggs down this time.
Any idea why I have such inconsistent success? Do I need to wait a little while before collecting eggs? Is it possible to squish eggs without actually breaking them? Do the eggs need to be kept moving with a tumbler? And why have I had wildly different success rates using exactly the same methods?

@NCaquatics ?

Ive yet to have my paleatus breed, but I do notice the cories who lay eggs in big clusters have higher rates of infertile eggs...

Example:
My aeneus spawned, I collected over 200 eggs from one female. Only 27 hatched.

I find eggs laid one by one have higher fertility rates.

Its not anything you are doing wrong.

Add an airstone, add alder cones, that will prevent most fungus

I've been doing some research on cory eggs and other eggs. I was especially interested in this blog post claiming a 90% hatch rate with exactly the same species of cory. Though it could be a fluke, I'm curious to try a few things to see if it improves my hatch rate.
I've read in a few places that the eggs should not be exposed to air at all. I do remember moving the eggs through the air as quickly as possible on the latest successful collections. But this was only once. Maybe they are more susceptible to air damage when they have just been laid?
I seem to be able to get my fish to spawn consistently two mornings after a water change, so perhaps in a week or so I'll try that and report back.
On a related note, does anyone know how often a cory can and should be induced to lay? I accidentally got her to lay two batches four days apart. Just seems like it might be bad for her to constantly put all her energy into egg laying.

EmilyS said:

I've been doing some research on cory eggs and other eggs. I was especially interested in this blog post claiming a 90% hatch rate with exactly the same species of cory. Though it could be a fluke, I'm curious to try a few things to see if it improves my hatch rate.
I've read in a few places that the eggs should not be exposed to air at all. I do remember moving the eggs through the air as quickly as possible on the latest successful collections. But this was only once. Maybe they are more susceptible to air damage when they have just been laid?
I seem to be able to get my fish to spawn consistently two mornings after a water change, so perhaps in a week or so I'll try that and report back.
On a related note, does anyone know how often a cory can and should be induced to lay? I accidentally got her to lay two batches four days apart. Just seems like it might be bad for her to constantly put all her energy into egg laying.

Click to expand...

They will lay with or without your intervention if they start and if conditions are right in *their* opinion

when i bread cories (bronze) i would remove the adult fish rather than move the eggs, the fry are extremely sensitive to everything, it is best to feed them live shrimp that are about a day old (they die when they get into the fresh water), light just makes it annoyingly worse so have them in a dark room. also DO NOT over feed, this will cause a fungus bloom and very low survival rate.

if possible do as little to the tank as possible.

if you want them to spawn do a water change, and drop the tank temp by about a degree or so for about a day or so, this triggers the females biological rain detector (the fish think that it has rained)

Thanks for the advice. I haven't had any problems with getting fry to survive, though I do consistently have a few newborn fry that disappear. Not sure why since my breeder box is made of mesh so small that even danio fry don't risk falling through. It happens even when the only thing in the box is newborn fry, and once they are a few hours old they stop disappearing.

After quite a few weeks and four batches of eggs, here is what I've found:

Baseline:
The last batch I collected from my first post actually had 6 good eggs out of 103. That's a good/bad rate of 5.3%.

Leaving the eggs in the tank for 24 hours before removing them:
Out of 72 eggs, 26 were good. That's way higher than before, but still way lower than I would expect, and lower than I know is possible. I moved the eggs to my breeder box and all 26 hatched. I do wonder if the waiting period only needs to be an hour or so. Breeders that remove the eggs, after all, tend to do so at the end of a breeding session, which can easily last an hour.
Good egg rate: 36%

Never exposing the eggs to air:
75 eggs, 11 good eggs. Took a little cup and used that to transport the eggs from the tank to the breeder box without taking them out of the water.
Good egg rate: 14.6%

No feeding before breeding:
Since I feed my corys in the morning as soon as I get up, I thought maybe excessive eating before breeding could be affecting the fertilization rate. It was the only possible difference I could remember for past batches of eggs. When I saw they were going to breed, I decided not to feed them. Out of 44 eggs I had 6 good eggs. I would definitely want to experiment with this more before drawing any conclusions considering it was such a small batch of eggs, among other things.
Good egg rate: 13.6%

Leaving eggs in the tank and letting the fish eat them:
Left the fish for 24 hours alone. The catfish laid the morning I was away and I came home that night to only eight eggs left. The eggs had probably been laid about 15 hours before. What's really interesting is that all of the eggs were good. My eggs usually turn white between 18 and 24 hours after they are laid, so there was no way of telling visually that the eggs were good or bad when the fish ate them. There must be some way that the fish "tell" which eggs are good and which are bad, though, because eggs left to the mercy of the fish almost always have higher hatch rates. Maybe the good eggs stick more to the glass and so are harder to eat?
Good egg rate: 100%

Main conclusions:
- The eggs are very fragile when first laid. Hatch rate can be increased by waiting before removing eggs, though I don't know how long you need to wait
- The fish can tell before I can which eggs are good and which are bad, and tend to eat more bad than good ones
- At best, it seems only a third of the eggs that are laid will actually be good eggs

I'd be curious to know what other people think, and if anyone does any of these experiments again I would love to know what you find.