Other than pellets and various frozen foods, raw shrimp (cooking it destroys all the nutritional value) raw fish fillet, probably any other crustecean, (although I doubt you are going to pay to feed your oscar lobster meat) beef heart is okay, because its basically pure protein, and hardly any fat. Any mammal or bird meat isn't good because it has too much fat. Live foods like earthworms, crickets, any insects or spiders you find, etc. Using feeder goldfish too much is unhealthy, especially if you don't QT them. Other types of fish are better. I'm not sure if they will eat it, but you can also try various vegetables.
