To call this an "aquarium simulator" is a gross overstatement. If anything, a screensaver simulator, perhaps?
There is little (alright, close to nothing) to actually do and whatever you do has no effect at all. If you don't "feed" your "fish" (which resemble more a poor cartoon approximation, even in cartoonish style), nothing happens. If you pack 500 fish in the tank, same as if there were 2, except you get more eggs, which you then have to click one by one to harvest (I've garnered around 400 in one sitting after two hours with the game closed), which gives you more money... with which you can buy, well nothing much really. Just more of the same fish approximation.
All in all a disappointing effort. I wouldn't mind the bad animation and poor cartoon fish if the game mechanics were a little more involved.

EDIT: Went to bed for 8 hours. Opened my game again. 80% of my fish had died from starvation? Age?. So things you do actually *do* have an impact on the game. If you sleep, you lose your fish. I don't think that happens with real fish but what do I know?
So basically Aquarium Simulator is a game that happens mostly when it's closed.
And if you're wondering, I had 1480 eggs to harvest. That's 1480 clicks for 154K in-game credits to spend on more fish that will die tonight. Nope.