It takes approximately 2 hours for fish to reach breeding age on the fastest game speed.

There are a number of things that can cause fish to die:

• Feeding your fish too much or too often can harm them. If you feed them before they are hungry (about halfway down on their "Fed" meter), they will lose health each time you feed them.
• Fish can also lose health and die if they are too fragile to survive in the level of Fish Environment that you currently have. Only the common fish (the ones that you can hatch from common eggs) can remain completely healthy in a Level 1 Fish Environment. The very fragile hybrids will usually not live to adulthood. Vitamins will temporarily improve their health, but only the proper Fish Environment will solve the problem.
• Of course, sick fish will die if you don't cure them!

Part of the challenge of Fish Tycoon is discovering different species that will help you succeed. There are several fish that will survive in a Level 1 Fish Environment (the one you start the game with) that will sell for more than $75. If you're impatient, there are resources in our Fish Tycoon Guide Section that will help you.