Hello,
Today fishes are kept under stable, warm conditions. In early days of aquaristics nearly all species where kept in colder water than today, especially in winter. During the cold period, the fishes had the chance to recover themselves. This was right and important for subtropical fishes – but is it healthy for tropical fishes? I dont know.
I keep my Paros at 22-23°C and they spawn permanently.
I dont know if 22-23°C are the temperature-optimum of that species, but it works.
Greetings