My male platy is the father of the four females in the tank. Mom died about six months ago and we figured dad was just get along with the females once they got older. He was always a little guy but they are MUCH bigger. They might be pregnant. However, they have soundly rejected him and he wanders alone in the tank, sometimes just hanging with the catfish. The females are wild and all over the place and literally will bump him and he has started to hide. He also looks smaller or are the girls just bigger. What gives?
Are you absolutely sure they are all female? In my swordtails (they are pretty much the same fish anyway) I've noticed that late developing males are a common occurence, fish I thought were female in the start turn out to be male.
I have had many cases of these "late bloomers" who turn out to be male when they get bigger. Maybe one of your females is actually a male now, and because he's bigger, simply bullies your other male out of the picture. Observe your fish and make sure. There is a very aggresive hierarchy among males in these types of fish. The smaller one will always be bullied if there are not more than 2 to spread the aggresion on. This leads to it being forced to hide 24/7.