Had a similar experience years ago. Had Convicts in a 29g with an under gravel filter. Tore the tank down partially and let it sit for almost two months in a cold basement. Went to clean it out and found 3 relatively large cons in the small amount of water left in the tank, under the under-gravel filter. I couldn’t believe it.
When I was just getting into the hobby I had kuhli loaches and ended up finding some fry from them in a sponge filter I cleaned out. I don't know how I bred them or how they got in there, but I didn't complain, I loved those guys so much
wow... I have a 407 canister on my 80G but I doubt any of my cichlids or sharks are ready to breed yet lol
but congrats... The only fry I got were guupy and platy from my 40G