Ok sorry didn't see you do feed him pellets.. but along with lots of fish
And I say "a lot" because frankly more then a few feeder fish a week is too much. Their just made for treats, not for the main meal.
Also a RES will eat, that doesn't mean he needs to, because in nature they have to eat because they don't know when their next meal is. So if your RES is bigger then normal maybe that's because you're over feeding him. He may be begging you because he knows you'll give in.
Watching him eat feeder fish is fun but shouldn't be a regular meal. Mainly because it doesn't actually fill him up from what I have seen with my adult RESs. They can eat salmon or some other fish I pick up for them the size of their body (basically as much I can eat) if I gave them that much. Since fish aren't really nutritious for them, give them pellets first then maybe vegetables. If they crave meat maybe give them crickets