The Feeding habits are different for each species. We will find, especially amongst the Ocean living species and the species that live in the Coral Reefs (for example: Arothron and Canthigaster) many Aufwuchsfresser (which predominantly nourish themselves from algae and therein hidden Micro Organisms, lower organisms like Coral, Sponges, Sea Sheaths) etc.
Most Puffer Fish however, dine mostly on Hard Shelled creatures, like Snails, Mussels, Sea Urchins , big and small Crustaceans.
Some, so called ,Predatory Puffer Fish, have specialised themselves to hunt small fish, for example: Tetradon miurus, Monotrete suvattii and Monotrete palembangensis. These are real ‚€œsit and wait‚€? hunters and even in an Aquarium mostly eat fish. The Commercial Fresh and Brackwater Puffer Fish , mainly need Snails to keep their teeth short.
Most of the known species will also eat other Live -or Frozen Foods ( a few species will even eat dry food) but the main part of their diet has to be dead or live Snails.
Some fewer species are very specialized, when it comes to their diet, for instance , some Auriglobus species, are specialized in fish fins, or insects, and some only feed on Octopus. With the species, that predominantly feed on soft foods, their death is predicted. As no one knows, how they manage to keep their teeth short in their natural habitat.
It is important, that in an Aquarium, you give your fish the same foods, that they would also get in their natural habitat.
Salt water species should receive food from the sea and Freshwater fish should receive their food from Freshwater or from creatures that live on land. Brackwaterfish can of course, be fed foods from both of the previous stated.
Puffer fish are very greedy. And easily overeat. As this is not good for them, it is suggested that they are fed in small but more frequent amounts. It is even healthy for them, to starve for one day a week.
A wide choice of different foods is advised, as with any fish.