my guys will eat tuna now and then, salmon sometimes if i can find it cheap. but smelt, market shrimp, catfish nuggets, frozen krill and chicken breast strips are the bulk of their diet.
i found that tuna and salmon fed too often or too much at a feeding will turn the water in your tank cloudy. so even though i get tuna chunks for just over $1 lb they still don't get tuna more than once a month, mostly less than that.