It’s not totally clear what Zynga has been feeding FishVille, but the results are now obvious: The virtual aquarium application has reached 9.24 million users, according to AppData. The game actually launched early this month, but wasn’t being promoted through Facebook advertising or on Zynga’s toolbar until the 8th or so, from what we can tell.

But what a past week this game has had. FishVille was taken offline for 36 hours last weekend because it was running rule-breaking advertising offers — and once it came back online, its traffic actually lurched downward. We wondered if Zynga had turned off advertising for the app at some point last week, given its lack of growth. The ads, or whatever Zynga has been doing, are back, because lately it has been gaining millions of new users every day.

If there was any question that Zynga might not be able to follow its hit games FarmVille and Café World with a new one, forget about it. Virtual aquariums are the latest popular genre of game — we now count six with more than 1 million monthly actives, led by CrowdStar‘s Happy Aquarium, which has 27 million monthly actives. Zynga has a history of building games that closely follow existing hits from other developers, then adding its own variations on the game mechanics and combining all that with its formidable active user base and advertising warchest. With FishVille, this formula appears to be working once again.

And that’s despite Facebook tweaking the news feed that the company optimized some of its game-play around, like getting users to share actions from a game into their feed. While there’s a long list of potentially handicapping changes coming from Facebook in the next couple of months, Zynga’s “playbook” for hit-making is for now doing just fine.