光泽铅笔鱼 · Shining Pencilfish

Overview

Uncommon in quantity, Nannostomus nitidus has a brightly colored male stripe above the main dark flank stripe. Questions about its relationship with similar pencilfishes mean the presence or absence of an adipose fin alone is not a secure identification.

Distribution & habitat

It was described from Igarapé Candiru-Mirim in the Capim system of Pará, Brazil. The Capim joins the Pará near Belém. Similar fish reported from Santarém and farther southeast at Fortaleza still need confirmation.

Slow tributaries, small rivers, and swamps with plants, wood, and leaves are probable habitats rather than a fully documented description.

Aquarium setup

Provide at least about 60 × 30 cm of floor space. Dense planting and dark substrate suit it well, with interrupted sight lines reducing nervousness. Floating cover, branches, and dry leaves add shelter; microorganisms on decomposing leaves can supplement fry food.

Use gentle filtration, normally an air-driven sponge unit, although some current is acceptable.

Diet & feeding

It naturally eats tiny invertebrates and other zooplankton. Offer appropriate-sized preparations with daily Artemia nauplii, small water fleas, grindal worms, and similar live or frozen foods.

Behaviour & compatibility

It is relatively peaceful but competes poorly with much larger or very boisterous fishes. Similar-sized peaceful characins and smaller bottom-dwelling catfishes are useful options. Evaluate other small fishes individually. Sedate surface dwellers such as hatchetfishes are best avoided, particularly in small tanks.

Middle-to-upper activity and infrequent fry predation make it useful with suitable dwarf cichlids, without guaranteeing no predation. Keep at least ten where possible to distribute social pressure and improve confidence.

Sexual dimorphism

Males are generally slimmer with stronger markings. Their anal-fin rays are also slightly thicker than those of females.

Breeding

This is an egg scatterer without parental care. Well-conditioned fish spawn regularly, and occasional fry may survive in a mature aquarium. To improve yield, prepare a separate dimly lit tank with aged water and protect eggs using mesh, artificial grass, marbles, fine-leaved plants, or spawning mops.

Use slightly acidic to neutral water toward the warmer end of the established range, with gentle aeration or sponge filtration. Introduce a conditioned pair, or one or two males with several females. More fish increase egg predation, while multiple males may distract each other from courtship.

Remove adults after two or three days; the first fry may appear about three days later. Start with Paramecium or fine preparations around 5–50 μm, adding Artemia nauplii or microworms as they grow.

Notes

Although normally described as having an adipose fin, approximately 24% of offspring in one captive observation from wild parents lacked it. This prompted questions about the boundary with Nannostomus limatus. Tooth arrangement and the third body stripe also differ in published diagnoses, so one small fin alone should not decide identity.

After dark, camouflage blotches or bars can replace the daytime appearance. This normal day-night rhythm does not establish nocturnal behavior.