Neon Tetra (Paracheirodon innesi)

Paracheirodon innesi's signature blue stripe isn't pigment at all, it's structural color: a layer of iridophores that reflects light like a prism, which is why the stripe seems to shift and brighten depending on the angle you view it from and even dims slightly when the fish is asleep or stressed. Discovered in Peru's blackwater tributaries in the 1930s, it's been a staple of the hobby for nearly a century and still the fish most people cut their teeth on. Shoal it properly and that structural blue turns into a shimmering, moving line through the tank.

Care level: Easy · Temperament: Peaceful, shoaling · Max size: ~1.5" · Min tank: 15 gal · Diet: Omnivore, flake/micro-pellet