Profile Photo

Maximum size : 3.5 cm

Coral Red Pencilfish - Nannostomus mortenthaleri : Complete Fish Profile & Care Guide

Table of contents


The captivating Coral Red Pencilfish, (Nannostomus mortenthaleri) a relatively recent addition to the fishkeeping hobby, was accurately described only in 2001. Initially considered a subspecies of the Dwarf Pencilfish, it was later acknowledged as a unique species in its own right. Coral Red Pencilfish are petite, active, and charming, making them an excellent choice for nano or well-planted aquariums. However, their small size and somewhat timid nature render them less suitable for typical community aquariums. For successful cohabitation with other species, opt for smaller, non-aggressive species like smaller Tetras, Micro Rasboras, and dwarf Barbs. Coral Red Pencilfish can also coexist with peaceful Corydoras Catfish and Plecos. As ideal dither fish for Apistogrammas and other Dwarf Cichlids, they generally inhabit the middle to upper areas of the aquarium and do not prey on fry. Though inherently social, Coral Red Pencilfish are shoaling rather than schooling fish, with rival territorial males engaging in frequent sparring. A spacious aquarium with décor arranged to create numerous broken lines of sight is essential. Ideally, these fish should be kept in groups of at least 10, with larger groups promoting natural behavior and improved displays while mitigating aggression. An ideal aquarium setup for Coral Red Pencilfish comprises a dark substrate, heavy planting, sheltered areas, floating plants, driftwood branches, and dried leaf litter. Gentle filtration, such as an air-powered sponge filter, is recommended. As these fish necessitate stable water conditions, avoid adding them to a biologically immature aquarium. Coral Red Pencilfish are small and slender, with males displaying red coloration on their entire body and fins, while females exhibit a pinkish hue. Both sexes feature two prominent, thick, lateral black stripes and a white base at the anterior portion of the dorsal fin in males. Recently, a Super Red Coral Pencilfish variant has emerged in the hobby. Yet to be formally described, it is currently designated as Nannostomus sp. \"Albertini Super Red\", as this stunning fish may eventually be classified as a completely new species of pencilfish.

Coral Red Pencilfish Photos

Sexual Dimorphism

Distinguishing between male and female Coral Red Pencilfish is straightforward. Adult males are more slender and exhibit more vibrant colors than females. Additionally, males display a white marking at the base of their dorsal fin from a young age. Observing their behavior can also help determine their sex; males often engage in displays and nipping at each other, while females remain docile and more passive.
Featured Male
Featured Female
Male Female

Quick Facts

Scientific NameNannostomus mortenthaleri
Year Described2001
Other NamesPeruvian Red Pencilfish, Ruby Red Pencilfish, Red Arc Pencilfish,
Max Size3.5 cm
Aquarium LevelMiddle - Top
DifficultyBeginner - Intermediate
Best kept asGroups 5+
Lifespan3 - 5 years

Water Parameters

Water TypeFreshwater
PH4.0 - 7.0
GH1 - 12
TDS18 - 90
75 - 82
24 - 28

Natural habitat

The Coral Red Pencilfish is a remarkable species that call the Nanay River Basin in Loreto Department, Peru, home. However, these fish have also been spotted in the Rio Tigre River system, just a little further to the west. These exquisite fish thrive in the tannin-stained, slow-moving, and soft acidic waters of small rivers, swamps, and floodplain lakes. Their preferred habitat is characterized by dense growths of aquatic vegetation and submerged woody arrangements, as well as a healthy layer of leaf litter. From their striking appearance to their unique environmental requirements, the Coral Red Pencilfish is truly a fascinating creature. Whether you are an experienced aquarist or simply an admirer of aquatic life, these fish are sure to captivate your attention and imagination.
 Nanay River - Peru
Peru Flag
 Rio Tigre - Peru
Peru Flag

How to breed the Coral Red Pencilfish

Breeding Coral Red Pencilfish is achievable but can be challenging for less experienced hobbyists. To begin, set up a separate breeding tank with mature water, a low pH level, plenty of fine-leaved plants or java moss, and marbles, pebbles, or small rocks at the bottom. Ensure the lighting is dim, and utilize gentle air-driven filtration. When the Pencilfish are ready to spawn, they will swim beside each other, with the male bumping the female's abdomen to fertilize the eggs. The female will then release a few eggs at a time, which will fall into the plants or substrate. Once all the eggs are laid, remove the parents to prevent them from eating the eggs. Depending on the temperature, the eggs will hatch within 36 to 72 hours. The tiny fry will first consume their yolk sacs and become free-swimming in approximately 3 to 4 days. After their yolk sacs are gone, feed the fry infusoria, rotifers, and powdered first foods, transitioning to larger foods like microworms and baby brine shrimp as they grow. With proper feeding, the fry should reach 1 cm in length in about two months and begin to exhibit the adult coloration.

Diet & feeding

Within an aquarium setting, Coral Red Pencilfish exhibit minimal fussiness when it comes to their diet, readily accepting a range of prepared foods such as micro pellets, freeze-dried food, and most flake foods. Nonetheless, to ensure these fish maintain optimal health and display their most vibrant colors, it is advisable to supplement their diet with live or frozen foods, including bloodworms, mosquito larvae, and brine shrimp.


Coral Red Pencilfish - Nannostomus Mortenthaleri - Rare Freshwater Nano Aquarium Fish Profile Thumbnail

9 tank mate ideas for the Coral Red Pencilfish

Looking for some awesome tank mate ideas for your Coral Red Pencilfish? Look no further! Here are 9 of the most captivating and fascinating options that will liven up your aquarium!

Other Pencilfish you maybe interested in