The fry really thrive on live food, but it is murder to keep them fed as they grow and their needs increase dramatically. So it is desirable to get them to accept a prepared food substitute. I used a gelatin food (about 50% protein on a dry basis and a consistency, at the start, about like toothpaste), starting at about 4 weeks when the fish were about ½ inch long.
Above: After a few days introduction, most of the 4 week old fry would go into an aggressive feeding frenzy when offered the gelatin food.
I offered the food and many fry accepted it immediately the first time. But it is a big change in diet from straight brine shrimp and some fry were slower to figure out that this green stuff was edible. So I continued to feed gradually decreasing amounts of brine shrimp over the next few weeks, finally (and thankfully) stopping shrimp production completely at about 6 weeks.
When preparing the gel food, it is important to really liquefy the ingredients so that little teeny fish can eat it all with no waste. This is a pain, particularly for ingredients like wheat germ that are hard to get reduced to powder. I made the food in 2 week batches so that it was always fairly fresh (cut it into daily portions, freeze the food, and store in marked, dated zip lock bags).
At about 3 months I also began feeding the fry (now about 1 to 2 inches long) a dried sinking food. I used the GFSA "Breeders Circle" food, which seems to work really well. This is a commercial trout starter food. I have used a couple of different versions of this, and the fish seem to be pretty flexible about this. The challenge has proven to be getting enough food into the fish without overwhelming the filter system.
Above: At 10 weeks, the babies are growing really fast and are more than ready for some dry food. The middle fish had a 3-inch body at 5-months.
One advantage to feeding gelatin food and a dry food is that the baby fish really need to be fed a lot to get proper growth. The gelatin food helps avoid the dangers of impaction from a dry-food-only diet. And the dry food packs a very high nutrient density per unit volume. So I think it is a good compliment.