I've found that a fish year on this game is about 5 mins. long when you're in 2X speed.
And a fish pregnany takes 4 fish years to complete.
So a fish pregnancy goes on for about 20 mins. in 2X speed, which is 40 mins. in normal time, and 1hr and 20 mins. in 1/2 speed.
And a fish year would be 10 mins. normal time and 20 mins. 1/2 speed.
I hope you found this helpful!