I found this.
Puffers are primarily predatory fish in the wild, though they do graze on algae as well. Acceptable foods include shellfish, crustaceans and hard shelled foods such as snails. A large variety of all kinds of live and frozen meaty foods are best. It is best to feed small amounts several times a day. Some of the suggested frozen foods include prawn, crabs/crabs legs, bloodworms (live or frozen), blackworms (live or frozen), silversides, and mussels. Be sure to wash these foods thoroughly before feeding. Live foods can include snails, crabs, crayfish, shrimp (these are good for keeping their teeth trimmed), and earthworms. Live fish will also be eaten but it is thought it may cause problems such as 'fatty" liver and so should be fed sparingly or not at all.. Puffers are not picky eaters and will quickly become adapted to a variety of prepared aquarium foods and an occasional algae wafer. Flake food is not recommended. Even though they may eat it, puffers will not thrive on it.