Pencilfish Care Tips

A shoal of peaceful pencilfish fish would make a great addition to your freshwater aquarium.

Pencilfish are some of the most beautiful and underappreciated fish in the hobby. They are small, peaceful and hardy once they adapt to a tank. Pencilfish are not seen that often in the local fish stores because they are generally collected from the wild; commercially raised fish appear infrequently. Since they are such small fish, they are usually shipped with hundreds of fish to the box, and pencilfish do not ship well. That said, when you do see them in your local fish store, I strongly encourage you to purchase some.

Pencilfish Care

Pencilfish are small (most are between 1.5 to 2 inches in length) and very peaceful. The only time you may witness mild aggression is between males sparring over females. They are similar to killifish, in that they prefer a quiet and heavily planted tank with just a little water movement. In addition to stem or rosette forms of plants, keep some kind of floating plant over a third of the tank surface. The more densely planted the tank, the more you will see your pencilfish, as the plants make them feel secure, and secure fish will come out into the open more than scared fish.

These are excellent community tank fish, as long as there are no fish in the tank that are larger than them or that will compete with them for food. Pencilfish are very slow, selective feeders, and they will not be able to  compete for food against any larger or more exuberant fish. In fact, they do best if kept in a species tank, with perhaps a few small catfish. Pencilfish do best in a school of five or more. Because they are so small, you can keep 10 or 12 pencilfish in a small aquarium. They would make a great display for one of the small packaged aquariums in the 6- to 8-gallon range. As mentioned, make sure to plant the tank as heavily as possible.

Feeding pencilfish is usually not a problem, as long as they do not have to compete with other fish for food. If you look closely, you will notice that all pencilfish have very small, pointed mouths directly at the end of the nose. This tells you that they require very small food, and they will take food from the middle to lower levels of the tank. Pencilfish are “pickers” and are deliberate feeders. They are constantly investigating every nook and cranny of their tank for small delicacies. They will do best if you feed them frequently (say, three to four times a day), but only as much as they will eat in a minute or so. Very small frozen foods, such as baby brine shrimp or very small Cyclops, will be eagerly taken, and they will also adapt to any prepared flake food, as long as you grind it up to be very small. There are some new gel foods coming on the market, and these are perfect for pencilfish to pick on. They will learn quickly when food will be forthcoming, but even then they do not eagerly flock for it as other fish do.

Some Suggested Pencilfish

The care of all pencilfish is pretty much the same, so I will briefly discuss three of the most commonly seen species. They all prefer warmer water in the high 70s to low 80s (degrees Fahrenheit) and soft and acidic water conditions. The pH can be between 5.8 to 7.3 for all species, and they will adapt to medium hardness, though they prefer water on the softer side.

Dwarf pencilfish (Nannostomus marginatus). Dwarf pencilfish are found wild throughout the lower to middle Amazon River Basin. The dwarf pencilfish can grow more than an inch in length and is distinguished by a broad central line running from the nose to the tail, with paler lines above and below the dark one. There are small red dots on the fins, with the exception of the tail.

One line pencilfish (N. unifasciatus). This pencilfish is also native to the Amazon River in South America, though its native range also extends to Bolivia, Venezuela and Guyana. The one line pencilfish gets to be about 1.5 inches in length, and it has a single broad gold line running the entire length of the body from the tip of the snout to the end of the tail.

Black stripe pencilfish (N. harrisoni). Nannostomus harrisoni is probably the most commonly seen pencilfish in the hobby. It is thinner and has a pointier nose than other pencilfish, and it can reach close to 2 inches in length. It has a single broad line running from the nose to the caudal peduncle (where the tail meets the body). The bottom of the tail, as well as the anal and ventral fins, have varying amounts of red in them.

Whichever species of pencilfish you are lucky enough to find, make sure that they have been in the store for at least a week before you purchase them. Keep them in a heavily planted tank — or better yet in a tank by themselves, in schools of five or more. Feed them often on small amounts of tiny foods, and you will enjoy them for a long time.

David A. Lass has owned and operated retail pet stores and a wholesale fish import/distribution business. David is also moderator on


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Fish · Freshwater Fish