The blue platy reads as steel gray-blue in most light and only flashes blue at certain angles, so shop photos tend to oversell it. Its color is a reflection rather than a pigment, so it depends on the lighting far more than a red platy's does. It is an easy, peaceful fish for a community tank.
Did you know
The blue platy's color is a physics trick rather than a paint job. Guanine crystals stacked inside iridophores reflect light, and the spacing between the layers decides which wavelength comes back. Change that spacing and the same cells throw a different color, which is why a blue platy slides toward gray or violet as it turns.
Caring for the blue platy
Keep blue platies in a small group, in a tank of 10 gal (38 L) or larger. Plant it, but leave some open swimming space. They swim mostly in the middle of the tank.
Blue platies are hardy and forgiving. Keep the water neutral to slightly alkaline, at 68 to 79°F (20 to 26°C) and a pH of 6.8 to 8.0. They handle harder water well. Feed a varied diet of flakes with some algae or vegetable content, plus the odd frozen treat.
They are peaceful and mix easily with other calm community fish. Keep more females than males to ease the pressure on the females, which grow a bit larger than the males.
Blue platies bear live young rather than laying eggs, and they breed readily. A female can store sperm and produce several broods from one mating.
Good to know
The blue platy is sold as a form of Xiphophorus maculatus, in the family Poeciliidae. Labels run Blue, Coral Blue and Blue Wag. Lines differ in how gray or how violet they look, and the depth of the sheen varies between batches.
In the wild
The blue platy is a selected form of domesticated platy stock, which by now mixes more than one Xiphophorus species. The usual hobby account is that breeders thinned the yellow and red pigment until the fish's own reflective layer dominated. Wild platies are drab olive with no sheen of this kind. No originating breeder or date is recorded.
Weekly picks
Tank mates
The blue platy is a peaceful, social species that keeps to the middle. These picks share a community profile with it, are safe together in both directions, and overlap on water type, temperature and pH.
2.8 in (7 cm)15 gal (55 L)68–79°F (20–26°C)
2 in (5 cm)16 gal (60 L)68–79°F (20–26°C)
4.1 in (10.5 cm)29 gal (110 L)73–82°F (23–28°C)
2.8 in (7 cm)24 gal (90 L)68–81°F (20–27°C)
5.9 in (15 cm)20 gal (76 L)68–82°F (20–28°C)
3.5 in (9 cm)29 gal (110 L)68–79°F (20–26°C)