This is a discovery that I made by accident. I have tried to keep a strain of Fundulosoma thierryi going for some years now. Thierryi fry are tiny and really difficult to raise, especially for the first 2 weeks.
One day while harvesting some daphnia I found 3 ¼ inch fry. They turned out to be thierryi fry. They had thrived in the daphnia tank! The nasty cloudy yeasty daphnia tank! I usually use my old tank water to refill the daphnia tanks, so I must have accidently transferred some thierryi eggs to the daphnia tank. Now I’m not a genius, but I know a good thing when I see it, so naturally I took advantage of this discovery.
Since the accidental discovery I have used the “dump em in the daphnia tank” method for various hard to raise fry. I’ve had excellent luck with Blue-Eyed Rice Fish fry, which are among the tiniest fry Ive ever seen. And it’s worked with just about every fry I’ve tried.
Another fry trick is to put them in a tank jam packed with Java Moss. Java Moss has millions of tiny organisms living among its tiny fronds, all just about bite size for tiny fry.
Just thought I’d pass along this discovery. It has helped me a lot with the “difficult” fry in my life.