Coral Red Pencilfish Care Guide - Aquarium Setup, Diet & Breeding

The Coral Red Pencilfish is a striking miniature characin with a slender, pencil-shaped body and vivid coral-red colouring. Dark horizontal markings and contrasting black patterning give the fish a particularly dramatic appearance, while mature males often develop the richest red tones and a more sharply defined display pattern.

This species is peaceful but lively, spending much of its time in the middle and upper levels of the aquarium. Males may spar and display to one another, flaring their fins and intensifying their colours, but these encounters are generally harmless when the fish are kept in a suitably sized group.

In the wild, Coral Red Pencilfish are associated with tannin-stained, slow-flowing waters beneath dense rainforest cover. Leaf litter, submerged roots and overhanging vegetation create a dim environment filled with cover, and the species is adapted to the warm, soft and often acidic conditions typical of South American blackwater habitats.

Nannostomus mortenthaleri was described relatively recently and has become highly valued in the aquarium hobby for its intense colouration and small adult size. It is sometimes confused with other red pencilfish, but its bold pattern and exceptionally vivid coral hues make it distinctive.

Coral Red Pencilfish come from the upper Nanay River basin in the Loreto region of north-eastern Peru, South America. They inhabit slow-moving blackwater streams, shallow forest pools and small tributaries associated with the Amazon basin.

A group should be kept in an aquarium of at least 45 litres, with a footprint around 60 by 30 cm or larger. Use gentle filtration and subdued lighting, with plenty of fine-leaved plants, floating cover, driftwood and shaded areas that recreate a sheltered blackwater stream. A dark sand or fine rounded-gravel substrate helps the fish feel secure and shows off their colours; tannins from botanicals or wood can be beneficial when water chemistry remains stable and the aquarium is well maintained.

Up to around 4 cm (1.6 inches); males are usually slightly slimmer and may reach a marginally greater length than females.

Feed Coral Red Pencilfish a varied diet of appropriately sized foods, including high-quality small granules or flakes, baby brine shrimp, daphnia, cyclops and other tiny frozen or live foods. Live and frozen offerings help maintain their colour and condition, while several small meals are preferable to one large feeding because of their tiny mouths and modest appetite.

Coral Red Pencilfish are well suited to peaceful community aquariums containing similarly small species, such as ember tetras, small rasboras, other pencilfish, otocinclus and appropriately sized Corydoras. They can also live with gentle dwarf shrimp, although newly hatched shrimplets may be eaten. Avoid large or boisterous fish, fin-nippers, aggressive species and most larger cichlids, which may intimidate or prey on them.

Coral Red Pencilfish are egg-scattering spawners that can be bred in a separate, mature aquarium with very soft, acidic water, subdued lighting and fine-leaved plants or spawning mops. Condition a group with plenty of small live or frozen foods, then introduce the adults to the breeding setup. Eggs are scattered among the plants and the adults should be removed after spawning, as they may eat them. The eggs usually hatch within two days, with free-swimming fry accepting infusoria or other tiny first foods before moving on to newly hatched brine shrimp.

Males are generally more intensely coloured, particularly through the red body markings, and have a slimmer profile with more pointed, elaborately displayed fins. Females are usually paler and deeper-bodied, especially when carrying eggs.