Once they get to 5-6", they start taking just about everything, including pellets, flakes, frozen krill, brine, etc. As Oddball noted, they are notoriously fragile when small though. As filter feeders, they need to be fed frequently when young, i.e., several times per day. Older Heterotis can get by with daily feedings or even occasional off days without feeding, as they've built up the necessary fat storage to survive such off-days.