Male Platy is aggressive against members of its own kind
I have 3 male and 1 female Platies in my aquarium. All of them always got along well with each other until the largest male and the female had offspring. Now the male always chases the other males.
this is unfortunately normal with this gender ratio. Male Platies are actually aggressive against members of their own kind, especially if there are (as in this case) too few females.
What can I do?
I see only one possibility - separate the fish and generally make sure to always keep at least as many females as males when keeping livebearers. It is advisable to keep only one male with one or several females per aquarium (unless it is a very large and/or a very densely planted tank), especially in case of platies and, even more, swordtails.
Dr. Bodo Schnell