I don't think fish, even live bearers, have menstrual cycles. They would have period(s) during the year where their hormone cycles might change in order to prepare them for spawning or impregnation but I don't think they would be classified as menstrual cycles.
Wikipedia: menstrual cycle:
The menstrual cycle is a recurring cycle of physiologic changes that occurs in the females of several mammals, including human beings and other apes. Humans are the only species that has a menstrual cycle with concealed ovulation. Other placental mammals experience an estrus, or heat, where imminent ovulation is signaled to the males of the species.