So here's the thing. In casual game masters PopCap's latest title - now out on the shelves of the UK thanks to a deal with Focus Multimedia - there's a fish tank that you need to populate with fish. Fish cost money, but you start off with a bit, so that's not a problem.

Then there's the food. You need to click on the fish tank to drop food, which the fish will try to eat. Leave a fish too long without food, it dies. Feed them well, they reward you with coins. There is, if you haven't worked it out yet, a suspension of disbelief that will be required right around now.

The money you accumulate you can then spend on upgrades. It might be more nutritional food that will leave your fish satisfied for longer between feeds. It might be the ability to drop an extra piece of food at a time, for at the start only one item can be dropped, and another can't enter the field of play until it's been eaten or fallen to the bottom. Or it might be more fish, because that way you'll get more money, quicker. The money, incidentally, you need to pick up by clicking on it, otherwise it drops to the bottom of the tank.

But what's this? Every now and then, an alien pops up in your aquarium, and must be defeated by clicking on it as much as possible before it can eat all your fish.

Fortunately, help is at hand. You can upgrade your alien blasting weapon, for instance. And there an assortment of creatures who are introduced as you progress through the game. These may help fight the aliens, or collect coins, or give birth, or ... well, there's quite a list. And as the game progresses, you must choose which of these powered beasties you want to take onto a new level. Choose wisely; trust us on this.

The ultimate aim of each level is to buy an egg at the end of it, which costs a lot of money. So a lot of mad clicking at the screen, a lot of money collection and a lot of fish appears to be the order of the day. In fact, so much mouse clicking is required that there's a sporting chance your finger will develop an involuntary twitch as a result of a quick Insaniquarium session.

That said, it's a fun, casual game to play, and very much designed to be played in small doses (the game's main mode, the adventure mode, saves your progress automatically, so you can jump in and out at will), not least because you'll go bog-eyed in addition to experiencing finger pain if you play for too much longer.

It's not a PopCap classic in the mould of Bejeweled or Zuma, both of which Focus has also punted out onto the shelves of UK software sellers, but it is worth a tenner.

You might want to account for a new mouse as part of your budget, though...

A good, solid PopCap casual game that easily relieves you of ten minutes at a time. And puts you off owning fish for life. Watch out for RSI.