Purple Pencilfish

About

The purple pencilfish (Nannostomus rubrocaudatus) is a small but boldly colored characid from the soft, acidic waters of Peru, and it's one of the more behaviorally interesting members of a generally peaceful genus. Males are the showstoppers here, displaying rich red-to-purple pigmentation running between three distinct dark lateral stripes, with a red anterior dorsal fin and reddish ventral fins that fade to clear at the tips. Females are more subdued but still carry hints of red in the rear half of the body. Worth noting: like most pencilfish, this species shifts to a noticeably paler, washed-out pattern at night when the lateral stripes effectively disappear, which can alarm new keepers who aren't expecting it. That color change appears to be automatic, even occurring in specimens without functional vision. Despite a "beginner" care rating, this fish rewards some extra thought in setup. Males spar frequently and persistently, and in a cramped or sparsely decorated tank real injuries can happen. A roomy aquarium with plenty of broken sightlines and a group of ten or more individuals helps distribute that aggression naturally. It pairs well with small, non-pushy tank mates, and works surprisingly well as a dither fish alongside Apistogramma and similar dwarf cichlids, occupying the upper water column without threatening fry.