The Coral Red Pencilfish Nannostomus mortenthaleri is one of the most beautiful species of pencilfish. It is a newer hobby addition that was only been scientifically described since 2001. it was discovered by and named for Martin Mortenthaler, the owner of the Austrian export company Aquarium Rio Momon in 2000. This pretty little fish was first described as a sub-species of the Dwarf Pencilfish Nannostomus marginatus, but then shortly after as its own distinct species.
This pencilfish It has a red body color with two strong horizontal black lines, giving it a broadly striped appearance. It is also known as the Red Arc Pencilfish, Peruvian Red Pencilfish, and Ruby Red Pencilfish. This is one of the most beautiful characins available today. Yet it vies for this position with an even more recently discovered pencilfish relative, the Purple Dwarf Pencilfish Nannostomus rubrocaudatus, described in 2009. These two are very similar in color, but only the Coral Red Pencilfish will have a white belly.
The males and females are both very colorful but when the males are displaying to each other, their colors are incredible! Just like the Siamese Fighting Fish, the males can be tricked into displaying by the use of a mirror. They believe that their reflection is another male so they have to show off.
This pencilfish is a very eye-catching, friendly, and active attraction. In size, it only reaches barely over and 1 inch (2.9 cm). It is a great addition to any community tank containing other small peaceful fish. It won't do as well with larger peaceful fish, simply because it is easily intimidated and won't be able to compete with them for food. Of course its small size could also make it a nice little snack for larger angelfish, gouramis, or catfish species.
Coral Red Pencilfish should be kept in a group of at least 6 fish. The males of this species can be aggressive towards each other but usually little damage is done during their fights, especially if the tank has lots of plants. If you plan on having more than one male in your tank, to be safe you should keep as large a group as you can to keep aggression to a minimum. Also never have more males than females. The males tend to drive the females hard so keeping a balanced ratio is needed to keep any individual females from being stressed. Fortunately they aren’t aggressive towards other species so the Coral Red Pencilfish are a good community fish.
The Coral Red Pencilfish Nannostomus mortenthaler was described by Paepke and Arendt in 2001. This species is not listed on the IUCN Red List. They are found in South America, specifically from the Rio Nanay in Peru, and also said to be found in the Rio Tigre near Santa Elena. These fish inhabit forest streams and tributaries. Other common names they are known by include Red Arc Pencilfish, Peruvian Red Pencilfish, and Ruby Red Pencilfish.
Scientific Name: Nannostomus mortenthaleri
Social Grouping: Groups
IUCN Red List: NE - Not Evaluated or not listed
The Coral Red Pencilfish, true to its "pencilfish" name, has a elongated body that is pointed at the snout. It will grow to just over 1 inch (2.9 cm) and has an expected life span of 5 years. It has a beautiful red body color with two strong horizontal black lines, giving it a broadly striped appearance. The lower portion is paler and often white. Males are the more brightly colored sex and have a white patch at the base of the dorsal fin.
Size of fish - inches: 1.1 inches (2.90 cm)
Lifespan: 5 years
Fish Keeping Difficulty
The Red Arc Pencilfish is a bit difficult to keep and is best suited for an aquarist with fish keeping experience. Most are wild caught specimens which tend to be less tolerant of varying water conditions than commercially bred fish. These freshwater pencilfish are prone to ich, especially when first introduced to a new aquarium. It is suggested they be acclimated in a quarantine aquarium before being placed in their permanent home.
Aquarium Hardiness: Moderately Difficult
Aquarist Experience Level: Intermediate
Foods and Feeding
Since they are omnivorous they will generally eat all kinds of foods. The Coral Red Pencilfish is not a picky eater so they will eat most prepared fish foods including small pellets, freeze dried foods and most flakes foods. To keep them looking their best, brine shrimp (live or frozen) or frozen blood worms should be fed occasionally. Keep in mind that their mouths are very small, so foods need to be crushed or minced in order for them to be able to eat it.
Diet Type: Omnivore - Their mouths are very small, so foods need to be crushed or minced in order for them to be able to eat it.
Flake Food: Yes
Tablet Pellet: Yes
Live foods (fishes, shrimps, worms): Some of Diet
Vegetable Food: Some of Diet
Meaty Food: Some of Diet
Feeding Frequency: Several feedings per day
Coral Red Pencilfish are moderately hardy. They are not exceptionally difficult to care for provided their water is kept clean. Water should be changed on a regular basis, especially if the tank is densely stocked. At least 25 - 50% of the tank water should be replaced every other week.
Water Changes: Bi-weekly
They are more difficult to keep than many other tetras. The water conditions should be kept rather soft and acidic for them to thrive. Peat filtration is advisable as this blackwater native is very intolerant of harder and more alkaline water. These fish are best kept in groups or 6 or more so they need about a 15 gallon long tank or a 20 gallon aquarium. They will swim and feed mostly at the surface of the water. The tank should be tightly sealed as this fish is apt to jump out of the tank if provided the opportunity.
The aquarium should be dim with a dark substrate to bring out their best colors. It also needs to be well planted with some floating plants at the surface to help subdue the light. Although they will appreciate some floating plants, because they eat at the surface, some clear areas need to be provided as well. They will also appreciate some driftwood decor to help provide plenty of places for retreat.
Minimum Tank Size: 15 gal (57 L) - They need at least a 15 gallon long or 20 gallon aquarium.
Suitable for Nano Tank: Yes
Substrate Type: Any
Lighting Needs: Low - subdued lighting
Temperature: 72.0 to 82.0° F (22.2 to 27.8° C)
Breeding Temperature: 78.0° F
Range ph: 5.8-7.0
Hardness Range: 2 - 10 dGH
Water Movement: Moderate
Water Region: All - The Coral Red Pencilfish will swim in most parts of your aquarium.
The Coral Red Pencilfish can be kept singly, but like many characins they are a schooling fish and more comfortable with a group of their own kind. They will be best kept in a group of at least 6 fish. Males will rival with each other, but with a heavily planted aquarium there usually isn't any serious damage. If you plan on having more than 1 male in your tank, to be safe you should keep as many as you can afford to keep aggression to a minimum. There should also be be fewer males than females, or an equal number of each as males tend to drive the females hard. Too much constant pestering can stress individual females.
Fortunately these fish aren't aggressive towards other species so the Red Arc Pencilfish make a good community fish. However they will be better with other smaller fish as they can be intimidated by larger peaceful fish and won't be able to compete with them for food. Of course their small size could also make them a nice little snack for larger fish like angelfish, gouramis, or catfish species.
Same species - conspecifics: Yes - Best kept singly or in groups or 6 or more. Males can be aggressive towards each other, so in a group keep as many as possible to spread out aggression.
Peaceful fish (): Safe - They are best with other smaller peaceful fish as they can be intimidated by larger peaceful fish.
Semi-Aggressive (): Threat
Aggressive (): Threat
Large Semi-Aggressive (): Threat
Large Aggressive, Predatory (): Threat
Slow Swimmers & Eaters (): Monitor
Shrimps, Crabs, Snails: Safe - not aggressive
Sex: Sexual differences
The males have an obvious white patch at the base of their dorsal fin. The best way to sex these fish is to look at the outside edge of the anal fin. It is a bright, deep red in males and is much paler in females. During spawning the males overall color will become much brighter. Another method of sexing is watching their behavior, males will frequently display and nip at each other and the females are very docile.
Breeding / Reproduction
This fish has been bred in captivity but not on commercial levels. Propagation is not impossible but a specific method hasn't been perfected due to the novelty of this fish. A separate breeding tank with soft acidic water should be the basis of attempts to breed. One successful breeder used a water temp of 78 F, with a pH of 6.6 and a total hardness of 20 ppm. For a description of breeding characin fish, see Breeding Freshwater Fish: Characins.
Ease of Breeding: Difficult
As with most fish, Coral Red Pencilfish are prone to skin flukes, parasitic infestations (protozoa, worms, etc.), parasitic infestations (protozoa, worms, etc.), bacterial infections (general), and bacterial disease. Anything added to a tank can bring disease, not only other fish but plants, substrate, and decorations can harbor bacteria. Take great care and make sure to properly clean or quarantine anything that you add to an established tank so not to upset the balance.
A good thing about the Coral Red Pencilfish is that due to their resilience, an outbreak of disease can often be limited to just one or a few fishes if you deal with it at an early stage. Stressed fish are more likely to acquire disease. The best way to proactively prevent disease is to provide the proper environment and a well balanced diet. The closer to their natural habitat the less stress the fish will have, making them healthier and happy. It is recommended to read up on the common tank diseases. Knowing the signs and catching and treating them early makes a huge difference. For information about freshwater fish diseases and illnesses, see Aquarium Fish Diseases and Treatments.
These characins are sold as the Coral Red Pencilfish as well as under the name of Red Arc Pencilfish, Peruvian Red Pencilfish, and Ruby Red Pencilfish. This is a relatively rare species and the price can be quite high. But it has been tank spawned and hopefully they will be breed on commercial levels so the price will drop.