Can anyone tell me what I am doing wrong? I donwloaded the program, clicked on the little fishes icon -- the icon appears in my dock for about 2 seconds and then disappears. I contacted the support site, but haven't heard from them. Any help will be very much appreciated! Thanks!

Can you tell me how much VRAM is installed in your Mac? The symptom that you're describing sounds very much like what happens in Macs with inadequate VRAM.

Thanks so much for your help! I'm not sure how much VRam is installed--it looks like 256mb, but I don't think I'm looking in the right place (I know, I sound like a dunce).

Here's how to find how much VRAM is installed in your Mac:

Click on the Apple icon in the upper left corner of the display. Click on About this Mac. On the popup window that results, click More info...
The System Profiler will be displayed. In the left pane, there should be listed something like Graphics/Display (may vary depending upon your Mac's model and age). Click on that and you'll see your display specifications in the right pane. Your video memory will most likely be displayed as VRAM (total).

If it's less than 32 MB, you probably can't run Fish Tycoon.

Thanks for your help--I think I got it!!!