Is my platy harassing the other one or are they just schooling?

[fanyfin]

I got a group of 3 platys. One is very young (about an inch long) while the other two are bigger (about 2 inches long). Out of the bigger two, one is constantly following the other one (and never the other way round) and at very close proximity.

The question that I have is : is the chaser a male who is just always trying to mate with the other one who is female? Or is this just normal schooling behavior where they just go in the same direction?

To me they both seem to be male based on the underside backside fin which is thin and long on them both. But the way one is always following the other (and never the other way round) and at so close proximity, it is giving me concern that it may be stressing the other one out. Should I be concerned or is this just normal schooling behavior?

[Autumnsky]

With a small group, the chaser's attention is focused on the one apparently, and it may be a female but yes it is likely to tire the one getting chased out. Stressing it out to the point of becoming ill.

It is best to get 1 male and 2 or 3 females, that way the chasing will usually be divided up more and at least some time to rest a little between attention chasing spurts.

A male will have a pointed fin next to the anal vent.
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