Shining Pencilfish

About

The shining pencilfish (Nannostomus nitidus) is one of the lesser-known members of its genus, occasionally turning up as bycatch in shipments of other South American species rather than being actively collected and sold. It originates from the Capim River basin in Pará, Brazil, where it presumably inhabits soft, acidic blackwater environments typical of that region. Males are distinguished by a brightly colored lateral stripe sitting above the primary dark body stripe. A combination that, along with details like scale counts and fin ray structure, separates it from closely related species. Like other pencilfish, it undergoes a dramatic color change after dark, switching from its daytime pattern to a cryptic series of vertical bars. This shift is hardwired into the fish and happens even in blind individuals, so don't be alarmed when you catch it in a different outfit first thing in the morning. It's a peaceful, somewhat shy schooling fish that does best in groups of ten or more, where individuals are bolder and any minor squabbling gets distributed across the group. It occupies the middle-to-upper water column, which makes it a useful dither fish alongside Apistogramma and other dwarf cichlids. Keep it with similarly sized, calm tankmates. Boisterous or much larger fish will leave it stressed and outcompeted.