双线铅笔鱼 · Twostripe Pencilfish

Overview

Small and timid, Nannostomus digrammus usually shows two dark longitudinal stripes, with the upper one sometimes less distinct. It is uncommon in trade and often arrives incidentally with other fishes. A quiet, densely planted group aquarium is appropriate.

Distribution & habitat

Known records cover the Madeira, Branco, Trombetas, and Tapajós in the central Brazilian Amazon, plus Guyana's Rupununi system. Although the Rupununi belongs to the Essequibo, seasonal flooding links it with the Takutu in the upper Branco drainage.

It inhabits slow tributaries, small rivers, and swampy areas with plants, submerged wood, and leaves. Similar fish exported from Colombia have an additional lower stripe, and occurrence in Peru is possible, but neither should automatically extend the confirmed range.

Aquarium setup

Allow at least about 45 × 30 cm of floor space. Dense planting, dark substrate, and ample cover reduce nervousness. Broken sight lines also help manage social encounters. Floating plants, branches, and dry leaves are useful, with leaf-associated microorganisms providing supplementary fry food.

Use gentle filtration; an air-driven sponge unit is usually sufficient. Avoid filling all available space with strong current.

Diet & feeding

It eats tiny invertebrates and other zooplankton in nature. Offer suitable-sized preparations with daily small live or frozen foods such as Artemia nauplii, small water fleas, and grindal worms.

Behaviour & compatibility

Its peaceful nature is offset by small size and timidity, making busy or highly competitive communities unsuitable. Similar-sized peaceful characins and smaller bottom-dwelling catfishes are better candidates. Middle-to-upper activity and lack of active fry hunting can make it useful alongside suitable dwarf cichlids, without guaranteeing that fry are never eaten.

Social groups are loose rather than constantly coordinated schools. Males spar regularly by day, and nipped fins may occur within the group, although this seldom extends to other fishes. Keep at least ten where possible to distribute pressure, with plants breaking sight lines.

Sexual dimorphism

Adult males are more colorful and slender, with a strongly modified, elongated anal fin that may approach the tail when folded. Females are usually fuller-bodied.

Breeding

Aquarium reproduction has not been reported.

Notes

The similar Nannostomus bifasciatus lacks the adipose fin present in this species. One body stripe runs along the middle, with another higher on the flank that may be less developed.

At night, oblique blotches or a vertical-barred camouflage pattern replace the daytime appearance. This day-night change does not establish nocturnal activity, and an altered pattern at first light is usually unremarkable.