Black Tetra (Gymnocorymbus ternetzi)

Gymnocorymbus ternetzi starts life with bold, high-contrast black bars over silver, then those bars soften and gray out as the fish matures, a pigment shift that's thrown off more than one new hobbyist checking for disease that isn't there. It's an old aquarium standby for a reason: fast-growing, unbothered by average water conditions, and a genuinely active midwater schooler. Keep the group large enough and any mild fin-nipping tendencies stay pointed at each other instead of slower tankmates.

Care level: Easy · Temperament: Peaceful, shoaling (mild fin-nipper) · Max size: ~2.5" · Min tank: 20 gal · Diet: Omnivore, flake/pellet