玛丽铅笔鱼 · Greenstripe Pencilfish

Overview

Rarely traded in quantity, Nannostomus marilynae sometimes arrives among other wild fishes, including cardinal tetras (Paracheirodon axelrodi). Three dark longitudinal stripes are typical. Its small size and relatively peaceful behavior suit a sheltered group aquarium with gentle filtration.

Distribution & habitat

Known records include the Brazilian Negro around São Gabriel and farther upstream and downstream, plus the Vichada in Colombia's upper Orinoco system. Venezuelan records still require confirmation.

Slow tributaries, small rivers, and swamps with plants, wood, and leaves are probable habitats rather than a fully documented account. The original collection description mentioned rock pools below rapids, which should not be interpreted as a requirement for strong aquarium current.

Aquarium setup

Provide a footprint of at least about 60 × 30 cm. Dense planting, dark substrate, and broken sight lines reduce nervousness. Floating vegetation, branches, and dry leaves add cover; microorganisms on decomposing leaves can supplement fry food.

Use gentle filtration, normally an air-driven sponge filter, although some water movement is tolerated.

Diet & feeding

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

Behaviour & compatibility

It competes poorly with much larger or very boisterous fishes. Similar-sized peaceful characins and smaller bottom-dwelling catfishes are useful candidates; small rasboras, barbs, and anabantoids require individual checks of behavior and conditions. Sedate surface fishes such as hatchetfishes are best omitted, especially 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 for confidence and to distribute social pressure.

Sexual dimorphism

Males are generally slimmer with stronger markings. The first five or six branched anal-fin rays are slightly elongated and thickened, but the modification is modest compared with that in some similar species.

Breeding

Aquarium reproduction has occasionally succeeded, and mature planted tanks may yield a few fry. For greater control, use a separate container with aged water and plentiful fine wool mops or fine-leaved plants. Strong lighting is unnecessary; a small air-driven sponge filter may be used.

After conditioning the group, introduce a pair or one or two males with several females. More adults increase egg predation, while several males may distract each other from females. Remove adults after two or three days; the first fry may appear another day or two later.

Begin with Paramecium or fine preparations around 5–50 μm, adding Artemia nauplii or microworms as fry grow.

Notes

It resembles Nannostomus minimus but lacks the strongly modified male anal fin of that species. Daytime and nighttime markings also differ from Nannostomus trifasciatus. An adipose fin is present, and the lower tail lobe is slightly larger than the upper one.

After dark, camouflage blotches or bars replace the daytime pattern. This normal day-night rhythm explains changes seen at first light and does not establish nocturnal behavior.