When will she give birth to her first fry?

My platy mated with a male around February 6th. Today she started breathing hard and swimming towards the bottom a lot. Is she closer to giving birth? This is her first time.

 

Probably in the next few days.

 

Probably in the next few days if you don’t move her to a different tank or move her to a breeding box.. If stressed by something like that she can stop the drop for this month.

 

Well, she doesn't look too pregnant. Which could mean that she's only delivering a few fry or she's at an earlier stage of pregnancy.

 

Live birth is always stressful for the mother. This is especially the case for a female giving birth for the 1st time. Typically, the gestation period is about 30 days, but this can be delayed if the impending mom senses that conditions are not right for release of her babies.