Taking care of fish seems to be a popular theme in the casual gaming space, be it feeding fish in Insaniquarium! or fending for yourself in the big blue in Feeding Frenzy 2.

And now we have Fish Tycoon, which is really a few games in one download. On one hand it’s a virtual pet and business simulation, where you must breed, grow and sell fish in your store, while your secondary goal is to find seven magic fish that have mysteriously disappeared from the island of Isola, and return them to their natural habitat.

While not perfect and not for everyone, the game proves to be a fun and challenging digital diversion.

At the start of the game, the optional tutorial introduces you to your virtual aquarium where you’ll see a few fish swimming about. You can use the mouse to tap on the glass (and see the little guys jump a bit), move items in the tank or drop items inside, such as sprinkling fish food.

To help your fish grow from teens to adults, you must buy some supplies such as food, vitamins or growth hormones. When you raise enough bucks – by selling fish in a pet store – you can buy optional items such as an aeration system ($70), cleaning snail ($80), diver ornament ($350) and even a second tank (in the registered version of the game).

By helping your fish stay healthy you’ll also to have buy medicine (such as fungal treatment) and help them mate by dragging and dropping two adult fish together in an isolation area. At any time you can set the price for your fish and drop them into a holding tank for your store visitors to see and purchase. The more money you make, the rarer the fish eggs you can afford, which in turn nets a higher price when sold, and so on.

You can also spend money to research a few things: technologies, such as new foods and chemicals to keep the fish healthy and happy; environments, which allows for rarer fish to survive; and advertising, on how to keep your store populated with deep-pocketed consumers.

Fish Tycoon boasts hundreds of fish species to grow, breed and sell, each of which has information about them by clicking a tab at the bottom of the screen.

The game runs in real-time, so if the computer is turned off (or if you leave the game for a while), smaller fish will be larger when you return – or a few other surprises may await you (both good and bad).

What about these seven magic fish, you ask? Without giving much away, you will eventually afford more expensive fish species and will soon discover which breeding combinations will create these swimming treasures to bring back to Isola.

The game, built on three main screens – the fish tanks, the supply room and the storefront (where little cartoon characters wander into your store to buy fish) – all are nice looking with detailed and colorful graphics. You can also click the Screen Saver tab for a virtual aquarium on your desktop, and even choose the species of fish.

The simple mouse-driven interface also works — with one exception. It’s not always clear what the little icons are on top of your screen, such as fish food, medicine, vitamins, and so on. Players should be able to run their mouse on top of each choice and the contents of the bottle should float on top to confirm what’s inside. Instead you’re taking a chance on dropping something into your tank you don’t want to.

A second issue: while Fish Tycoon is slow-paced and relaxing, it may not satiate casual game fans who are looking for a quick 5- or 10-minute diversion at the end of a lunch hour break. Instead, you likely need to play the game at least 30 minutes at a time to get something rewarding out of it. The good news, however, is the relaxing nature of the game-play means you can keep the game on while doing other things, such as reading email or surfing the Web, as long as you check back every once in a while.

Fish Tycoon is a fun and refreshingly different kind of download that folds in a virtual pet game, a business simulation and a mystery. While not for everyone, it’s certainly worth playing around for your 60 minutes of free play to see if the real-time game-play is for you.