All fish that I have experience with are predators to one extent or another. If it fits in the mouth they will try an eat it. Fresh, salt, brackish, or ornamental. It doesn't matter. The key is finding quality. I breed my koi, and they make millions of little ones. The culls are thrown to the Tilapia, bass, and catfish. Better and cheaper than any pelleted food. BUT, it's not consistent. And not always available. For little fish, when the season is on, mosquito larvae will make your babies grow like weeds. Simply net in a bucket with em, and rinse and feed. They won't last more than a minute or two.