How long to fish stay pregnant until they give birth on fish tycoon

Well, not too long. About 25 minutes. It should not be any longer than that. If you want it to go a little faster, you go to to Menu, and click on Options, and then click 2x Speed, or it should say something like that. When I get pregnant fish, they usually take about 20 - 25 minutes for me. But I have it on 2x Speed in the Options Menu.
What kind of fish? For most tropical fish their tummies get really big, they don't eat, and they just sit near the heater near the bottom of the tank.