pregnant fish

Question
My son has a very large aqurium we noticed one fish is very fat we are assuming shes pregnant,he went to the supply store they gave him a floating device to keep the fish in withing the large tank, how long do fish stay pregnant?

Answer
Hi Kathie,

First and foremost what kind of fish are we talking about here? the fact it has fallen pregnant without your son trying to breed them leads me to believe it's some kind of live-bearer, which would mean you don't have long.

Let me know!

Tom