Oscars and canned tuna?

You could, but not as a staple diet. Oscars are susceptible to malnutrition so be sure to feed a variety of pellets, night crawlers, shrimp, and beef heart. And tuna, seldomly, if he enjoys it.

In theory, yes, but in reality I would try a more balanced approach that will have less chance of polluting your aquarium.

I have made my own fish food before and it is important to have the right ingredients, and that includes WHOLE fish meal and other aquatic food sources. Oscars in the wild eat the whole fish and that includes the aquatic vegetable matter in the fish they eat's stomach.

Here is basic list of ingerdients from one of my articles:

BASIC/ GOLDFISH/ CARNIVOUR

Whole Salmon: 25% 20% 30%

Peas: 25% 25% 15%

Egg: 20% 15% 25%

Brine shrimp: 15% 15% 15%

Spirulina Powder: 10% 15% 5%

Wheat Germ: 0% 5% 0%

Squid: 0% 0% 5%

Fish Oil: 2% 2% 2%

Corn Starch or Gelatin: 3% 3% 3%

For my full article on proper fish nutrition, including how to make your own, please see this article:

http://www.americanaquariumproducts.com/Quality_Fi...

No, too many chemicals. It would mess up your waters ph. I would go with the pet stores frozen food for them.