Gameview Studios is one of many developers that saw huge hits on the iPhone, particularly with its Tap Fish game, which has been downloaded more than 10 million times on Apple’s App Store. Now the company is starting to see good results on Google’s Android mobile devices as well.

It’s still early and the Android results can’t yet match those on the iPhone. But the results are good enough to pleasantly surprise Gameview, which is a division of Japan’s DeNA mobile social game company. That’s good for the Android platform, and not so good for Apple. With these kinds of results, Gameview will be motivated to port more of its hit games to Android. Both Google and Apple are keenly aware that they’re competing for the hearts and minds of developers.

The company is announcing today that its free version of Tap Fish has been downloaded more than 500,000 times since a quiet launch on April 1 with no promotional activity. The game has been rated 4.5 out of 5 stars in more than 10,000 fan reviews. And it just surpassed Angry Birds Rio (the latest version of the hit game from Rovio) by taking the No. 4 spot in the Android Market’s top free apps list. Overall, the game is the top casual game on Android and ranks No. 15 for overall free apps.

John Hwang, vice president of products at Gameview, said in an interview that Android is becoming a better and better opportunity for social game makers. He noted that, on average, Tap Fish users log in more than three times a day to check on their aquariums. The retention over seven days is 85 percent, and users have visited more than 1 million of their neighbors’ tanks. Hwang said that the title spread through word of mouth and by its presence on the Android Market’s top game lists.

Hwang said the company hasn’t really begun to monetize the app yet, but it could deploy in-app purchases over time. Google just turned on the Android Market’s in-app purchases, which allow users to make a purchase of a virtual good or a game without having to exit the app. Apple has had this capability for some time, and it is fueling revenue growth among iPhone app developers. But Google’s in-app purchases are available only to users of Android 2.3 software, which is available only to a tiny percent of Android users right now. Still, Hwang believes that revenue from in-app purchases, particularly cross promotion of other titles, will be more important than ad revenue over time.

Hwang said that Gameview ported the game to Android because of the sheer volume of requests the company got from consumers who had seen the game on their friends’ phones. The porting work isn’t trivial, since there are hundreds of different types of exotic fish, 80 tanks, and lots of decorations. The company also decided to port the game because of Android’s growth rate. Gartner predicts it will become the world’s most popular operating system by the end of the year and could capture half the smartphone market in 2012. Google still has lots of room for improvement, but it’s moving forward, Hwang said.

With in-app purchases now available on Android, and with application storefronts such as the Android Market and others making Android apps easier to find, Gameview Studios plans on releasing many other titles on the Android platform over the coming months. Gameview has 15 employees in Mountain View and more developers overseas.

The company was founded in 2010 by Riz Virk and Mitch Liu, and it competes with rivals such as Electronic Arts, Magma Mobile, Outfit7, Glu Mobile and Digital Chocolate. Other Gameview games include Tap Ranch, Tap Jurassic, Tap Town, and Titans vs. Olympians.

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