Anything but Tetras! The Joy of Keeping Pencilfish

Author: Gary A. MacDonald

If you're bored of common tetras, pencilfish might make an excellent alternative for a schooling community fish. Learn about this small–mouthed and highly tolerant species, along with its complex yet rewarding breeding behavior.

My Happy Surprise

In fishkeeping, as with most things in life, a twist of fate will generally take you down a path that you may have never known existed. In my case, it all started with a free 50-gallon tank from my wife’s aunt (hey, Aunt Lou!) in Sarnia, Ontario in 2004. Just for fun, I started the tank on Halloween of that same year.

Preparing the Aquarium

After cleaning, resealing, and getting a nice stand for the tank, I planned my aquascape, which was eventually designed, planted, and filled with water. The cycling process was somewhat standard (aside from the usual small disasters, such as a broken filter and a mini flood), using established media from my 55-gallon freshwater planted tank. After this came the fun part—stocking the tank with fish.

My first course of action was, of course, some Otocinclus (see the author’s article, “Oto Pilot: Buying, Keeping. & Breeding Otocinclus Catfish,” TFH February 2008). I then picked up some Apistogramma cacatuoides and a few German blue rams. Nine Corydoras ambiacus later, things were taking shape. The lower levels were busy, but the middle and top columns were lacking something. In any case, the tank was a lush jungle at this point.

Looking for Schooling

What was missing was fish for the middle and top strata of the tank. Something that schools would be totally wonderful, I thought. “Anything but tetras,” I said to my wife one day as we were cruising local fish stores for something unique. For some reason, tetras just don’t do it for me.

But what other type of fish schools nicely? I didn’t want White Cloud Mountain minnows; I’ve owned them before, but they would not do as well in the warmer temperature (78°F) of my current tank as they would in an unheated setup. Then we stopped at one of the fish stores that I typically visit only if I am in the neighborhood.

Looking at row after row of fish in the store aisles (mainly tetras—neons, cardinals, rummynoses, and black skirts), I happened upon a tank that was in the right corner of the store with tiny fish inside. Some were silver with three horizontal stripes running down their bodies. The others were brownish, with hints of red and white. They were torpedo shaped, and every few minutes or so they’d form a massive school, which was very cool. But what were they?

My Introduction to Pencilfish

The sign on the tank read only “Just In!” and nothing more. I went through my mental faculty (which wasn’t as extensive at the time) and failed to come up with an ID on these little fish, which actually looked almost like Leporinus sp. to me. I inquired about the name of these fish, and after looking through some handwritten lists, the word “pencilfish” came up.

What I was looking at were two separate species (misidentified and lumped together, as usual). The first, which were silver with three horizontal lines, were Nannostomus trifasciatus, while the other was Nannostomus beckfordi, commonly known as Beckford’s (or golden) pencilfish.

After a week of research, I returned to the store and purchased seven of them. They acclimated quickly, and all of these originals are now among the massive colony of 21 individuals that live in a 75-gallon display tank in my living room.

Nannostomus beckfordi History

The first recorded Nbeckfordi was described by GÜnther in 1872. It comes from the order Characiformes (same as the fish commonly called tetras), the family Lebiasinidae, and from the subfamily Pyrrhulininae (which includes splashing tetras). Of the genus Nannostomus, 17 species exist, and 15 of those are available in the aquarium trade. Beckford’s and Harrison’s pencilfish are the only two that are commercially bred and available for the aquarium trade through breeders. The rest are always wild caught.

Nannostomus” was coined from Greek roots to indicate “small mouth.” These South American fish can be found over a wide geographical range, covering Colombia, Venezuela, Guyana, Bolivia, Peru, and Brazil, as well as the southern part of the Amazon Basin. Some variances occur within the distinct populations, but I figure that this is enough to get the scientific stuff out of the way.

Pencilfish Characteristics

Beckford’s pencilfish are slender, torpedo-shaped fish that rarely breach the 2-inch mark (yet may grow to 2½ inches). The grouping in my main tank consists of a range of different sizes and ages, from the recently born (and those that have just come out of hiding) to mature adults that are a couple of years old. Their slender appearance adds to their uniqueness in respect to schooling formation.

All Nbeckfordi share two characteristics. They all have a single, thick, black lateral stripe extending from the face to the tail. In addition, they all include red anal fins, coupled with red splotches on their caudal fins near the bottom on both sides.


The males, in particular, are noticeably a darker shade of brown on top. The black lateral stripe also seems thicker, and appears smudged, while the red anal fins and the blotches of red at the bottom of the caudal fin (on both sides) appear significantly larger. When they are in the store, most of the fish look tan and have more pronounced markings. But if you are specifically looking for a male, just check the fins (especially the anal ones), as they seem to be larger and longer.


In contrast, females typically have a smaller and more rounded anal fin. As with many fish, the males are much slimmer than the females. Ultimately, identifying them should be no problem. In a dealer’s tank, these little beauties deserve more than the brief glances they usually get when more colorful fish are in the area.

Pencilfish Husbandry

Keeping Beckford’s pencilfish requires very few demands of the average aquarist. I strongly suggest that these fish not be kept by beginners, as they are a bit sensitive and require careful acclimation and high water quality.

Beckford’s pencilfish can tolerate a wide variety of water chemistries, which makes them a great choice for most community tank setups. As always, look at intended tankmates, look at your tank, and consider the conditions needed to keep these fish before you make your decision. Naturally, it’s often wise to research before making such a commitment.

The water conditions they can tolerate include a pH range from 6.0 to 7.4 (6.5 is optimal), and a temperature range from 22° to 28°C (72° to 82°F). The aquarium can be as bright or dim as you want, but they will prefer the more dimly lit tanks over the brighter ones, especially if you wish to start breeding them. A densely planted tank will truly bring out the color of these fish, and their behaviors as well. Watching two or three males display to each other is really impressive.

Their natural environment is dense plants along the edges of rivers and streams in the wild. Naturally, these areas would be overshadowed by trees and branches as well. I try very hard to accommodate the needs of my fish by recreating their natural settings as much as possible.

Feeding Pencilfish

Feeding Beckford’s pencilfish is just as easy as feeding most fish in the hobby. Your standard aquarium fare should do nicely. But to really bring out their colors (and initiate breeding) you need to feed them a varied diet. I usually feed them bloodworms, tubifex worms, soft-bodied bugs (e.g., small crickets that escape from my daughter’s frog tank) and (frozen) mosquito larvae. Beckford’s pencilfish are extremely aggressive feeders, and if you have shy fish in the tank, they may not get their share when the Beckford’s are in town.

It’s always wise to vary the diet of your fish regardless of whether or not you want to breed them. It makes for happier and healthier fish that will live a long time. The lifespan of the Beckford’s pencilfish is about five years, but as usual, optimal conditions can extend the lifespan of any fish. I’ve heard rumors of them living more than six years.

Beckford’s Buddies

Tankmates should also be selected with care. Remember, these fish are slim and only grow to 2 inches. Putting them into a tank with a Ctenopoma means that all of your pencilfish will be gone in a short period of time, so choose with care. Overly aggressive fish that could swallow the pencilfish whole should be avoided at all costs. I keep mine with discus, angels, Mesonauta festivusApistogramma spp., Amano shrimp, kuhli loaches, blue emperor tetras (which like to school with the pencilfish), and of course, Otocinclus cats.

Beckford’s pencilfish can also hold their own. They prefer to be in groups with no less than three members. However, if you have the space, I would suggest cranking that up to five. Having a larger group will bring out more of the coloration and behavior that make these little fish quite interesting.

Danios and Barbs

They can be placed with danios and some barbs, but I suggest putting the pencilfish in the tank first, before starting to add more active tankmates, if you choose to do that. Once again, research is paramount. And I’ve often found that talking with other hobbyists also gives you an additional, more personal view.

Bottom Dwellers

Beckford’s pencilfish also serve as great dither fish for those shy and timid bottom-dwelling fish like Apistogramma spp. that look for visual cues to environmental changes. If the pencilfish are out and swimming, it lets the shyer fish know that it’s okay to come out and that the coast is clear. If they all dart for the dark corner of the tank, this serves as a visual cue for others to hide; it works very well.


When I introduced my two discus into the tank, my Beckford’s pencilfish immediately formed a large cohesive school with a leading alpha male in front. They formed a ball-like structure and hovered for a few minutes, moving a couple of inches at a time until the lead male investigated. Once he returned, the school broke down and everyone went to visit the two new tankmates. I find them quite curious and bold, all in one package—what more could you want?

Typically, the only thing that may stop us from buying these guys is the price. In my neck of the woods, they are all too common. I can pick them up for just over a couple dollars per fish. The most I’ve seen them for is about three times that much—luckily, though, they are easy to breed.

How to Breed pencilfish

For most of us, just keeping the fish is not enough. We also enjoy breeding our fish; whether it’s accidental (how it usually starts) or purposeful, it’s a wonderful challenge for the hobbyist. Fortunately, breeding Beckford’s pencilfish poses no special challenges compared with other egglayers.

Breeding in a community tank is very possible, and my situation reflects this. Every now and then, small pencilfish show up in the school. And on occasion, we spot a few fry hanging out underneath a Cryptocoryne leaf. But if you want larger volumes of surviving fry, a dedicated breeding tank is best.

Step 1: Establish a Breeding Tank

The tank should be no less than 10 gallons, though once again, I prefer 20-gallon tanks for breeding as often as possible due to the preferred footprint and better surface area. The tank should be dimly lit (usually just a single bulb works fine along with floating plants), with a dark bottom or substrate (placing a piece of black construction paper underneath the tank usually works if you don’t want to go the substrate route). The tank should also contain plants, particularly those with feathery leaves (Limnophila sessiliflora “dwarf ambulia” comes to mind), which are messy and happen to be great for hiding both eggs and fry. Java moss is generally a staple in all breeding tanks (for me, anyway), as it provides not only protection for eggs and fry, but also significant microfauna to feed the fry for the first few days of life.

Step 2: Get a Sponge Filter

A sponge filter is also a must. Sponge filtration provides many great services, including biological filtration, oxygenation, the growing of various fauna (on the sponge), and cover. With it, you can also avoid the sucking up of fry, eggs, or fish.

Step 3: Filter the Water

The water should be filtered through peat or have some sort of blackwater extract added to the tank to give it an amber color. Keep the tank temperature at 25°C (77°F).

Step 4: Move Fish to the Breeding Tank

At this point, slowly acclimate a group of fish (males and females at a ratio of one male for every two females) to the breeding tank. I would put in twelve fish to effectively increase your chances of success—this would be four males and eight females. Once they are in the tank, slowly start to increase the temperature to 29°C (84°F). Keep a backup supply of pre-warmed, oxygenated (air stones usually work) water handy, along with the incorporated blackwater extract. This is good not only for water changes, but for aging the water as well. I have had great success with pre-made water.

Step 5: Feed

Feed them well with live foods such as wingless Drosophila (or small and soft-bodied bugs). Once they are well fed and the water begins warming up in the dark tank, nature should take its course. First you’ll see the males displaying to one another, or to a female. If you happen to be watching, you will see the male drive the female into the plants and nudge her abdominal area. At this point, she will dispel an egg and the male will fertilize it. One thing that remains the same about all egglayers is that the parents are hungry after breeding, and those eggs happen to be wonderfully pre-made, nutritious treats. This is exactly why I include messy plants such as dwarf ambulia and Java moss in the tank, since most eggs will get lost in the mess and the parents will never find them. Others have tried a marble substrate which may work nicely as well, allowing the eggs to drop into places where the parents cannot reach.

Step 6: Remove the Parents

After the breeding process is done (usually in the early morning) remove the parents as soon as possible. When the parents and other fish are removed from the tank, the hard part comes next.

Rearing the Fry

The eggs will hatch in one to two days, depending on temperature. The warmer it is, the quicker the eggs will hatch, but the quicker the water quality can go afoul. Once I remove the parents, I keep the water at a constant 28°C (82°F) for a week or so. After one week, you are pretty much out of the critical stages of fry development. At this point, I turn off the light on the tank—even though the dark doesn’t seem to add a sense of security for the upcoming fry in those eggs, nor does it help against the fungusing of the eggs.

After the eggs hatch, the fry remain on the tank bottom. If you shine a light, they will jerk up into the water column about half an inch before settling back down again. They are still consuming their yolk sac, which is quite visible, and they stay at this stage for a couple of days. Next the fry start to cling to surfaces. They resemble small pieces of glass when you shine light into the tank. After 24 hours more, they are out and swimming, looking for their first meal.

From eggs hatching to swimming fry, four to five days have passed. This is the most critical of all stages. If you’ve made it this far and still have all or most of your fry, congratulations! Feeding your fry for the first time usually requires finely powdered foods and fauna from the Java moss and sponge filter. While not enough to sustain all the fry for long, the Java moss and sponge filter should be an excellent source of food for the first day of swimming.

I use finely powdered flake food (at the consistency of dust) as well. At day two of swimming, baby brine shrimp can be fed. I can’t emphasize the importance of water quality enough. I find that the fry develop quicker and the eggs seem to fungus less with excellent water quality. How I change the water is quite time consuming, but the end result is a larger amount of eggs and/or fry surviving. Remember that pre-made water? This is where it comes in—I keep an aquarium of 20 gallons full of pre-made, preheated, and pre-aged tap water mixed with RO and peat.

I take out 10 gallons daily with a large cup and take the water just off of the surface. I place the cup into the water gently (don’t disturb the babies) on a 45-degree angle with the mouth of the cup facing up, letting the water slowly pour in. When the cup is full, I dump it, usually using a small plastic bucket.

I then return the water in the same way that I had removed it from the tank, trying not to create a waterfall effect of water crashing into it. To remove debris and large pieces, I usually use a pipette to remove these, ensuring that I am not sucking up fry in the process.  When the fry reach a quarter of an inch, you will start to see the dull beginnings of the lateral stripe on the fish. I have, unfortunately, not spent the time to gauge whether or not temperature affects gender ratios in the fry.

Also at this size, your fish should be capable of eating crushed flaked food and smaller live foods. Once again, feed enough, but not in excess, and continue to keep a good water-change schedule going.

A Good Laugh

I’ve had this article on the back burner for some time now. The funny part is that I now own six Inpaichthys kerri, the blue emperor tetras. For reasons unknown to me, they school (cohesively) with my pencilfish. They often go off on their own, but 90 percent of the time, they stick with the massive school of pencilfish—so much for avoiding tetras!

But, tetra tankmates or not, I find Beckford’s pencilfish to be a welcome addition to a community tank, and a good change from the norm.

See the full article on TFH Digital