I've raised batches of swordtail fry on just crushed flake and they grew up fine but slowly. I've also tried various other foods. The fastest growth rate seems to have been on the batch that I've been giving freshly hatched baby brine shrimp, live microworms, frozen bloodworms and Hikari First Bites powdered flake food. (Obviousely not all at once). My current batch of fry I started with the baby brine shrimp and microworms for the first week and then added the Hikari First Bites and then started adding the frozen bloodworms about the second or 3rd week. They are 5 weeks old and I'm primarily giving them the First Bites now with the microworms and bloodworms every other day (more as a treat at this point). I also give them a little bit of mushed green peas about every 4 or 5 days (or whenever I make some peas for the adults). Just like the adults, they go crazy for their peas. A good variety of foods seems to give the best results as far as fast growth rate but be careful not to overfeed them. I also feed them 4 to 6 times a day.