Some publishers might be keen to experiment with in-app purchases, but there's plenty of evidence to suggest the model is a solid revenue driver as it stands.

First in the queue to leap to its defences would be US based studio Gameview, which has just announced that total download of freemium release Tap Fish have surpassed 10 million units on the App Store.

Tapping into success

According to the firm's figures, players have been just as keen to invest in the game as they were to download it in the first place, with Tap Fish placing as one of the top grossing free-to-play mobile games of 2010 thanks to the sale of virtual goods in play.

"We are thrilled with the success and longevity of the whole Tap Fish franchise," said co-founder Riz Virk.

"Our goal has always been to build really high quality sticky social games. One reason for the success of Tap Fish is that people think of these fish as their pets, enjoy caring for their fish, watching them grow, and showing them off to their friends."

Next up for Gameview, which was purchased by social gaming behemoth DeNA back in September, is the launch of Tap Fish on Android, with the studio planning to roll the game out on Google's OS later in 2011.