Hi Satai Delenn,
I have successfully played Fish Tycoon online, for weeks on end (before I purchased the game). And I was able to breed, find magical fish (yep they show up!), and keep most of my fish alive.

How about I give you a few of my tips:
1) don't use your spare eggs right away.
2) don't use your growth hormone right away either.
3) since you don't start out with any of the same fish, breed fish that are like finned or like body shape.
4) don't buy meds for the first fish that get sick before you make some money. After you have a little extra, then cure your fish.

I can give you more but I don't want to give too much away all at once in case I might spoil it for someone else reading.

The one hour Demo is different. The graphics are a lot better(!) for one, you won't lose as many fish in the learning process, and (as stated by LadyCFII) you'll have less bugs to deal with and more features.

I'm not a game buyer myself. But I was soooo hooked by the Demo version of Fish Tycoon that I changed my mind. I couldn't remember where I found it, went searching the internet for it, ran into Virtual Villagers, and the rest is purchase history...