In what can only be a gut-wrenching moment for the developers of aquarium simulations games like Happy Aquarium and My Fishbowl, Zynga received a trademark to the name “FishVille” last week. This almost certainly means that Zynga will launch a version of the game, and quite likely grow it quickly.

The trademark comes as the company enjoys the successful launch of Café World, a restaurant simulation that directly challenges Playfish’s Restaurant City. Café World grew by 10 million users in a week, through Zynga’s methods of cross-promotion with its other games, advertising on Facebook, and building increasingly high-quality game-play.

Café World itself follows Zynga’s launch of FarmVille, a farm simulation game that copies others, like Farm Town. And, before that, Mafia Wars, which copied Psycho Monkey’s Mob Wars, which itself was part of an intellectual property dispute with SGN. Copying is how things go in social gaming these days.

As spotted first by Trademork, the trademark for FishVille covers:

“computer game software, video games, online games, and game related applications; interactive video game programs; electronic games and game related applications that may be accessed via the internet, computers and wireless devices; computer software to enable uploading, posting, showing, displaying, tagging, blogging, sharing or otherwise providing electronic media or information regarding the fields of virtual communities, electronic gaming, entertainment, and general interest via the Internet or other communications networks with third parties” as well as “entertainment services, namely, providing computer games, enhancements for computer games, game applications, reviews of computer games, and information relating to computer games; providing an Internet website portal in the field of computer games, gaming and social networking; Entertainment services, namely, providing social games and information regarding social networking via the Internet”.

This is not to say that Zynga is the least original developer. FarmVille and Café World both use some original dynamics. If anything, improving quality is now a key part of Zynga’ strategy.

Which is why the aquarium threat is so real. At this point, it’s not clear what exactly will slow down Zynga. It is at least twice as large as the nearest developer on the platform — Playfish. Maybe something big, like a severe design change by Facebook, or the entrance of a well-funded competitor.

Happy Aquarium is made by a developer called CrowdStar. The app was just added to AppData, which shows CrowdStar’s other games totaling only 324,000 – Happy Aquarium alone has 10.2 million monthly active users. We’ve been tracking the progress of My Fishbowl lately as it has climbed up the charts. It’s a product of Chinese-language developer TwoFishes Interactive.

[Fish image from Zazzle via John Battelle]