Are my Corys using condoms?

[Jon_D]

A most pleasant and Healthy 2021 to all my Forum Friends and any visitors reading this.
On Friday , 3 days ago, I found about 15 – 20 eggs which my Corys had placed on the front of the tank. I collected and transferred them to the QT tank (2 gallons) as well as water from the CT. Yesterday they were still lying on the bottom but this morning I saw that all had hatched and the fry were dead! Not one had any eggyolk on their bodies. Just very tiny replicas of the parents. Any ideas why the eggyolk is missing? Previously the eggs from the same Corys were unfertilised.

[fr499y]

Still young ? might take a couple attempts.

[BigBen]

The yolksac on Cory fry isn't the big yellow thing you see on plecs etc. It's far smaller and less obvious.

[Jon_D]

@fr499y That sounds very like as earlier eggs weren't fertilised either. This is only the second time the 2 males with the single female have attempted mating. Many thanks. @BigBen , regarding the egg yolks, I carefully checked with a strong magnifying glass, and could see no sign of anything resembling that on any of the bodies.

[BigBen]

The yolk sac is easiest to see from above with young Cory's.

[plankton]

How old are the prospective parents?
Is the water the same in q-tank as the tank they're spawned in?

[Jon_D]

@plankton .1. Female is mature and I have managed to get her eggs hatched previously when she was in the CT . The 2 males are less than 4 - 5 months old. I think this is the second time they mated as previously they were ibn the CT tank competing with another 9 -10 males and were much smaller. (There were 15 Corys in all )
2. Water was taken from the CT but was NOT the water in which they were spawned. The is was the Tank 3 which I want to be for male Guppies. However I put the 3 Corys in it as I didn't think the 4 guppies would create enough ammonia to keep the water parameters constant. It was these 3 Corys which produced the earlier non-fertile eggs and now these. There have been 2 bathces of eggs in the past 3 months.

[plankton]

They are still pretty young at 5 months, so maybe the fry just aren't developing properly, despite the mature female?