Cenepa Red Pencilfish


The first photo of what was being called the ‘Cenepa red pencilfish’ showed a single, vivid red male without the telltale horizontal black stripe seen in Nannostomus mortenthaleri, the coral red pencilfish, a species known in the hobby for decades.

These fish truly live up to the hype surrounding their sudden appearance in the trade, with dominant males displaying an almost uniform, vibrant scarlet rarely seen on wild freshwater fish, extending into the dorsal fin and with a trim of black and white along the edge of the caudal and anal fins.

Juvenile and subdominant males start to develop the red colouration beginning at the face before it extends out towards the tail, and are
easily distinguished from the much more plain looking females.

Female markings resemble those of the ever-popular dwarf pencilfish, Nannostomus marginatus, with their only visible colour a splash of red in the dorsal fin and on the operculum.

Despite their diminutive size this new species fairly glows in the aquarium, darting around in typically frenetic pencilfish fashion, and occasionally aggregating into tight schools when startled or to travel across the length of their tank en masse.


At first collectors were understandably coy about revealing the collection location of this new Amazonian red jewel, but it appears
that the Cenepa red or super red pencilfish originates in the Rio Amaya, a small blackwater tributary of the Rio Morona, one of the
headwaters of the Amazon which in turn flows into the Rio Maranon about 600km upstream of Iquitos.

The Rio Amaya is deeply tannin-stained, clear, and with almost no discernible mineral content but little else is known about it. Blackwater
tropical rivers the world over have a tendency to produce some of the most vividly coloured tropical fish known to the hobby (e.g. the
cardinal tetra or blue Axelrod rasbora) and the Rio Amaya, home to this stunning new red pencilfish, appears to be no exception.

Despite the logistical hurdles needed to even reach some of these places (let alone get fish out to an exporter alive), as time goes on we’ll
likely see some of these currently unexplored regions become at least slightly better known. And in the case of the new Cenepa red pencilfish, if they become as popular in the hobby as they deserve to be, we may be fortunate enough to see a diversity of other species collected alongside them in the Rio Amaya make their way into the trade.

At the time of this writing several more species from the Rio Amaya have been offered, including a beautiful small tetra similar to Axelrodia riesei, but with a vivid orange rather than red body colouration. A colourful Ancistrus and a few other species supposedly from the region are also starting to make their way into the hobby.

Settling into a home aquarium

I received a group of Cenepa reds in early May and acclimated them to my home aquarium without incident. Being so superficially similar to the coral red pencilfish, which often succumb to bacterial infections post-import, I wanted to keep a close eye on these new fish, especially given their high price.


Fortunately, the precaution was not necessary, as the Cenepa red pencilfish proved to be extremely hardy and the whole group did well
without the need for any preventative treatment or exhibiting any signs of disease. The fish were carefully individually packed and made the long voyage from Iquitos to Denver in excellent condition.

Having to mostly guess regarding their wild habitat and preferred water parameters, I aimed for typical blackwater conditions, with a pH of 6.5-6.8, temperature around 28°C and the addition of lots of botanicals to keep the water rich with tannic and humic acids.

The fish fed readily on a combination of high-quality flake and fine pellets rich in the natural red colour enhancer astaxanthin. Maintaining a healthy blackwater tint in their aquarium by frequently replenishing the Indian almond leaves and bark also seemed to
improve the male’s already stunning deep scarlet coloration.

Overall Experience


Overall, my experience with the Cenepa red pencilfish has proven them to be extremely low maintenance, with some early
aggression among males easily diffused among the group as they developed a clear hierarchy. The largest and most dominant handful
of males display the most vivid, solid colour but rarely spar now that the group has settled in.

I would recommend keeping this species at a ratio of one male to two or three females and in a group of at
least 12 (of course a larger group will display more natural social behaviour). An abundance of fine branching driftwood or well planted
aquarium will ensure these fish are at ease in their aquarium, especially during the first few weeks after acclimation. Given the tendency of
all pencilfish to be somewhat shy, especially in the presence of larger fish, I would recommend the Cenepa red pencilfish as the centerpiece fish of their aquarium, with few, if any, tankmates.

The Cenepa red pencilfish — a spectacular swimming gem — is an unexpected but very welcome
addition to the hobby and I suspect the first spawning of this species will not be far off. This species is hardy, beautiful, and for the moment quite sought after. And its arrival in the hobby is a worthwhile reminder that in remote tropical streams, creeks, and swamps the world over there are certainly many more spectacular and unknown fish species. Some of these will undoubtedly take the hobby by storm in the coming years as they are discovered and described — assuming, of course, that the current onslaught of development and habitat destruction do not get to them first.