In my non-betta tank I have 5 Corys, I added 4 Zebra Danios which all died within a few days, even replacement Danios....then about a week later I noticed this tiny little guys swimming around.
I thought cool the Corys had babies, but I don't remember seeing any eggs etc etc. As the weeks have passed the 10 little babies have gotten bigger and bigger! Come to find out they are Danios!
Now it looks like one of my female Corys is getting VERY fat in the mid section!
I don't know what I am putting in the water in that tank but damn they have been busy LOL!