Two-striped Pencilfish

About

The two-striped pencilfish (Nannostomus digrammus) is one of the lesser-seen members of its genus in the hobby, turning up most often as an accidental inclusion in shipments of other species rather than as a deliberately imported fish. It's a slender, small characid from the Amazon basin and Guyana region, where it inhabits slow or still waters typical of lowland tropical South America. Its name comes from the two dark horizontal stripes running along the body, one along the midline and a second, usually fainter stripe higher up. Like most pencilfish, it also switches to a completely different nocturnal pattern of oblique blotches after dark. This color-shift appears to be hardwired rather than voluntary, since it occurs even in blind individuals. Adult males develop a noticeably elongated anal fin that reaches back toward the caudal fin when pressed flat against the body. Behaviorally, this is a shoaling rather than tightly schooling species, and males will regularly spar with each other during the day, sometimes leaving nipped fins within the group. This stays largely internal to the group rather than extending to tankmates. Keeping a group of ten or more genuinely helps spread that low-level aggression and brings out bolder, more natural behavior. Its small size and timid nature make it a poor match for boisterous community setups, but it pairs beautifully with Apistogramma and other dwarf cichlids, occupying upper water levels without threatening fry.