Nannostomus rubrocaudatus · Purple Pencilfish

Overview

Male Nannostomus rubrocaudatus develops relatively uniform purple-red over the rear body, with color between all three dark flank stripes. Before formal description it circulated under Purple and Coral Red II labels. Similar red trade names should not be assumed to identify the same species.

It is generally peaceful toward other fishes, but territorial males can injure each other in restricted space.

Distribution & habitat

The type material came from a wild-fish shipment exported from Peru to Germany. The importer reported collection near Saramirisa on the Marañón, between the Morona and Santiago rivers. If accurate, this places the site several hundred kilometers west of Iquitos near the Andean foothills. The precise locality remains conditional on that account.

Natural habitat has not been confirmed. Related species use slow water with plants, submerged branches, and leaves, but equivalent lowland habitats are not widespread in the reported foothill area. Those general conditions should not be presented as a verified collection-site description.

Aquarium setup

Provide at least 90 cm of tank length for a mixed-sex group. Dense planting and strategically placed wood must interrupt views and give subordinate fish escape routes from dominant males. Dark substrate, floating plants, and leaf litter supply further cover. Leaf decomposition also encourages microorganisms that may supplement fry feeding.

Keep filtration gentle, usually with an air-driven sponge. Stable conditions are essential; a newly established aquarium is unsuitable.

Diet & feeding

Wild fish consume tiny invertebrates and other zooplankton. In captivity, offer suitably small dry foods together with daily live or frozen items such as Artemia nauplii, Moina, and small worms.

Behaviour & compatibility

A species aquarium simplifies care, although tiny peaceful characins and small callichthyid or loricariid catfishes can be considered. Its usual position in the middle and upper water makes it a potential dither fish for dwarf cichlids. It does not actively hunt fry, but that is not an absolute safety guarantee.

Groups are loose associations. Territorial males display and spar regularly during daylight, more forcefully than most related pencilfishes. Serious injury or death can occur in cramped quarters. Keep at least ten alongside sufficient floor area and extensive visual barriers; adding fish without adding escape routes is not a solution.

Sexual dimorphism

Males are slimmer and more colorful, with thickened third through sixth anal-fin rays. Red-purple lies between the three dark flank stripes and becomes relatively uniform on the rear body. The front of the dorsal is red with a clear outer region, while pelvic and anal fins also tend to have red bases and transparent tips.

Females are fuller-bodied. The space between the upper two dark stripes is mainly silver, with a reddish line beneath the central stripe toward the rear and a small red patch ahead of the anal fin.

Breeding

Aquarium breeding has succeeded, and occasional fry may survive in mature planted tanks. For more controlled production, prepare aged water with abundant fine spawning yarn, moss, or finely divided plants. Lighting is unnecessary; a small air-powered sponge is an option.

Introduce conditioned pairs. If several pairs share the aquarium, separate the spawning material into distinct areas, for example at opposite ends with space between. Adults can be removed after two to three days, with fry appearing a day or two afterward. Another approach is to inspect yarn daily, moving egg-bearing material elsewhere and replacing it.

Start fry on Paramecium or foods graded around 5–50 μm. Add Artemia nauplii and microworms once the young can swallow them. Adult markings begin to develop at roughly eight weeks.

Notes

Compared with Nannostomus mortenthaleri, male purple-red is distributed more evenly across the rear body. Nonbreeding males of that relative concentrate red between the upper two stripes, have a white anterior dorsal-base mark, and more uniformly red pelvic and anal fins. Female silver interstripe areas and clear fin tips also aid identification here.

Night coloration becomes much paler, with the dark longitudinal stripes disappearing. In the similar species those stripes generally remain visible. An altered appearance immediately after lights come on is therefore not automatically a sign of illness.