Coral Red Pencilfish

Geographic Origin and Biotope: Exclusive to the Rio Nanay and Rio Tigre in Peru. Inhabits slow rivers and forest streams rich in decomposed organic matter in dark or amber waters.

Taxonomy and Morphology: Coral Red Pencilfish (Nannostomus mortenthaleri). Closely related to N. marginatus (of which it was once considered a subspecies), it features a compressed body and short snout.

Social Behavior: Fiercely aggressive towards conspecifics (unlike relatives). Males are incredibly hostile to each other; they duel constantly and injure each other if the tank does not guarantee sufficient escape routes.

Coloration and Sexual Dimorphism: Among the most spectacular freshwater fish in the world: dominant males light up in a glowing coral red (Red Coral) that covers the entire body between the three black bands. Females remain pale pinkish-yellow with horizontal bands.

Aquarium Setup: Very expensive and territorial species: needs a minimum of 80-100 cm (32-40 inches) to disperse the aggression of the males. Very thick visual barriers (dense forests of stems, branched woods up to the surface) are ABSOLUTELY fundamental.

Diet and Feeding: Micropredator. More ravenous than marginatus. Will avidly devour daphnia, freeze-dried brine shrimp and very high-end protein flakes to enhance the red pigment.

Water Quality: Sensitive and delicate fish: demands immaculate waters (Zero Nitrites/Ammonia) and weak filtration over peat (Ph 6.5) to keep the environment stable and partially calm the males' nerves.

Compatibility and Tankmates: Excellent with other species, but lethal with its own male kind. Can coexist perfectly with South American Dwarf Cichlids (Apistogramma, Dicrossus), Otocinclus and Corydoras, but NEVER in small tanks with more than one male of its species.

Aquarium Reproduction: Difficult, both because of the prohibitive prices of the breeders, and because the males often kill the rebellious females or each other before spawning. The eggs (very small) are released among the foliage.

Risks and Diseases: Intraspecific murder. Buying a school of 5 males for a 60 cm (24 inches) tank (common mistake, being the red ones) will lead to the death of 4 of them in a few days. If you want a school, you need 1 male for every 3 females (expensive, since females are rare and priced high in stores) in tanks of at least 1 meter (40 inches).