[link] (Full combined credits for the whole show, all episodes)
[link] (the first episode, which I was about to update, but then realized I should confirm more things before I delete people's credits when they may actually have worked on an episode.)
The IMDb credits, as I've said, are user-submitted and are usually based upon/copied from the on-screen credits after every episode. As you know, the end credits on the show are fixed for a season, with no customized credits for each episode. (This also means that many voice actors go uncredited, and other actors get credit when they weren't in an episode.)