Japan Blue Guppy
Poecilia reticulata
About this strain
Japan Blues carry a neon, electric-blue patch in the mid-body region — particularly vivid behind the pectoral fins — combined with a yellow or pastel tail. The blue is structural (iridophore-based), not pigment-based, so it shifts and glows under different light angles. This mid-body blue spot is the variety's calling card; the tail is typically a complementary but secondary feature. Japan Blues are a recognized genetic strain, not just a color morph, and cross readily to transfer the blue-body trait into other varieties. They're relatively peaceful and adaptable.
Origin
Developed in Japan during the 1980s–90s by hobbyist breeders working with naturally occurring iridescent coloration in domestic lines. The strain was later exported and refined internationally.