I have only played Fish Tycoon for 2 days or so, but everytime I want to continue playing and check on my fish, I have to restart. I know that all my fish have not died, because in the box of the things I have, I have fish eggs and the growing hormones. This means that my computer doese not continue the game, but starts it over every time...what can I do?

Which version of the game are you playing? Mac? Windows? The symptom you are seeing is typically caused by the game being unable to create or locate savegame files.

I am playing the mac version, but after trying a few times, it works now......but why are my baby fish dying all the time?

Check that you haven't made a rare baby fish, if you have, you will probably need Enviroment Research. So I would suggest you save up, buy Enviroment Research, and then try again. If that isn't the problem, I would check on your fish more frequently.