Dwarf pencilfish with shrimp

By the Shrimp Tank Hub editorsUpdated Oct 26, 2026Research-based

The dwarf pencilfish (Nannostomus marginatus) is a tiny South American lebiasinid with three dark stripes along each side. Seriously Fish lists it from Guyana, Suriname and the middle-to-lower Amazon in Peru, Colombia and Brazil, where it lives in sluggish streams, swamps and areas with dense plants, wood and leaf litter. AquaInfo notes that the stripes fade at night and two oblique bands appear instead, so a fish that looks odd first thing in the morning is usually fine.

Dwarf pencilfish at a glance

Will dwarf pencilfish eat shrimp?

• Adult shrimp: usually not. Our reading is that a fish about an inch long with a tiny mouth can't eat a grown cherry or crystal shrimp. But Aquarium Co-Op's pencilfish guide covers the whole genus, including bigger species, and says cherry and crystal shrimp are not recommended because pencilfish are known to prey on them. We take that as a real warning.
• Shrimplets: likely eaten. Seriously Fish describes the species as a micropredator of tiny invertebrates and zooplankton, and AquaInfo says the fish hunt small moving prey one at a time. Newborn shrimp are exactly that size. Practical Fishkeeping lists pencilfish among the fish that will almost certainly eat young shrimp.
• Eggs and berried females: safe. Shrimp carry their eggs under the tail.

If you want a striped microfish that is gentler on shrimplets, compare ember tetras with shrimp, chili rasboras with shrimp and kubotai rasboras with shrimp, or see the full cherry shrimp tank mates list.

Matching the water

Seriously Fish lists 72–82 °F, pH 4.0–7.0 and 1–10 dGH; AquaInfo prefers pH 5.5–7.0 and says a stable 24–25 °C (about 75–77 °F) suits most fish. Cherry-type shrimp tolerate 65–85 °F, pH 6.2–8.0 and GH 4–8 (The Shrimp Farm). By our comparison:

• With cherry shrimp: about 74–78 °F, pH 6.5–7.0 and GH 4–6 sits inside both ranges. Hard, alkaline tap water above pH 7 is outside the fish's range.
• With crystal and other Caridina: the soft, slightly acidic water these shrimp need (about pH 6.0–6.5) suits the pencilfish well, but the shrimplet risk is the same. See crystal red shrimp care and Caridina vs Neocaridina.

Stability matters most. Seriously Fish says the species needs stable water and should never be added to an immature tank, and AquaInfo warns that low KH makes pH swings more likely. See GH and KH explained, shrimp tank pH and shrimp tank water changes.

Tank size and setup

• Size: Seriously Fish asks for a base of at least 18 × 12 in, about a 10-gallon footprint. AquaInfo prefers 60 cm (24 in), or 80 cm for a bigger group, and Aquarium Co-Op likes a 20-gallon high or 29-gallon tank for pencilfish.
• Mature tank only: see how to cycle a shrimp tank. A tank with months of biofilm also gives shrimplets more food and cover (our note).
• Heavy planting, dark substrate: Seriously Fish recommends a heavily planted tank with a dark substrate, floating plants, wood and leaf litter. For shrimp, add dense moss where shrimplets can hide. See java moss for shrimp and driftwood and botanicals for shrimp.
• Gentle filtration: Seriously Fish suggests an air-powered sponge filter. See shrimp-safe filters.
• Lid: Aquarium Co-Op says pencilfish may jump if startled, so use a tight-fitting lid. See do shrimp need a lid.

Keep a real group

Seriously Fish says to buy as many as possible, ideally 10 or more: in bigger groups any squabbling is spread out and the fish are bolder. AquaInfo also recommends at least ten and says serious aggression between males is uncommon in this species. Females are fuller-bodied; males stay slimmer (AquaInfo).

Other good tankmates

Seriously Fish calls the species a poor general community fish because it is small and timid, and suggests similar-sized peaceful characins and small catfish. See pygmy corydoras with shrimp and otocinclus with shrimp. Avoid fast or boisterous fish that grab food first; AquaInfo notes the species feeds slowly.

Feeding both

Seriously Fish says dwarf pencilfish take small dried foods but should get small live or frozen foods such as Artemia nauplii, Moina or grindal worms every day. Aquarium Co-Op adds that their small, upturned mouths do best with tiny foods that float or sink slowly, such as baby brine shrimp, cyclops, daphnia and crushed flakes. AquaInfo suggests several small portions a day. Well-fed fish are less likely to hunt shrimplets (our reading), and sinking shrimp food can go in a separate corner. See best shrimp food.

How to add dwarf pencilfish to a shrimp tank

• Shrimp first. Let the colony grow large and settle into moss before the fish arrive (Practical Fishkeeping).
• Keep a backup colony in another tank if a shrimp line matters to you.
• Acclimate slowly. Most pencilfish in stores are wild-caught (Aquarium Co-Op), so ask what water they were kept in. See how to drip acclimate.
• Watch shrimplet numbers for a few weeks after adding the fish.
• Quarantine the fish separately. Practical Fishkeeping says many fish medications are not safe for invertebrates. If fish get sick, ask a fish veterinarian or an experienced store about treatment that won't harm the shrimp. See how to quarantine and is copper toxic to shrimp.

Common mistakes

• Adding them to a new tank or one with unstable water.
• Keeping three or four instead of a group.
• Feeding only big flakes they can't eat.
• Adding them to a shrimp breeding or selling tank.
• Keeping them with fast, pushy fish.

Track it

Log temperature, pH, GH and TDS on the free Water Parameter Log printable so you can keep the tank in the range both species share.

Frequently asked questions

Will dwarf pencilfish eat cherry shrimp?

Baby shrimp, yes. Seriously Fish calls them micropredators, and Aquarium Co-Op does not recommend pencilfish with cherry or crystal shrimp. Adults are usually too big for a fish about an inch long, in our reading.

Can dwarf pencilfish live in a shrimp tank?

In a mature, heavily planted display tank with dense moss, often yes. Expect shrimplet losses, and skip them in a shrimp breeding or selling tank.

What water do dwarf pencilfish need?

Seriously Fish lists 72 to 82 °F, pH 4.0 to 7.0 and 1 to 10 dGH, with stable conditions. With cherry shrimp, aim for about 74 to 78 °F, pH 6.5 to 7.0 and GH 4 to 6.

How many dwarf pencilfish should I keep?

Ideally 10 or more, according to Seriously Fish and AquaInfo.

How big do dwarf pencilfish get?

About 1 inch (25 mm standard length) according to Seriously Fish, or about 3.5 cm total length per FishBase.

What do dwarf pencilfish eat?

Tiny live and frozen foods such as baby brine shrimp, Moina and grindal worms, plus fine dry food. Seriously Fish recommends small live or frozen food every day.

Sources: Seriously Fish, Nannostomus marginatus (dwarf pencilfish) (Guyana, Suriname and middle-to-lower Amazon; sluggish tributaries, small rivers and swamps with dense vegetation, wood and leaf litter; 25 mm SL; 45 × 30 cm base; 22–28 °C, pH 4.0–7.0, 1–10 dGH; rated moderate because it needs a well-established tank and stable water; heavily planted, dark substrate, floating plants, wood and leaf litter; gentle air-powered sponge filtration; never add to an immature aquarium; micropredator of tiny invertebrates and zooplankton; small dried foods plus daily small live or frozen foods; very peaceful but timid, poor community fish; similar-sized peaceful characins and small catfish; ideally 10 or more); Aquarium Co-Op, Care guide for pencilfish (pencilfish genus guide: at least six of a species; 10 gallons possible, 20-gallon high or 29-gallon preferred; most store fish wild-caught; may jump if startled, tight lid; peaceful community tankmates; tiny floating or slow-sinking foods; cherry and crystal shrimp not recommended since pencilfish are known to prey on them); AquaInfo, Nannostomus marginatus (dwarf pencilfish) (about 3.5 cm TL per FishBase, around 2.5 cm SL; stripes change at night; serious aggression uncommon; micropredator hunting small moving prey; several small feeds a day, slow feeder; tank from about 60 × 30 cm, preferably 80 cm; at least 10; 22–28 °C, stable 24–25 °C; pH preferably 5.5–7.0; 1–10 dGH; low KH and pH stability; dark substrate, fine-leaved and floating plants); Practical Fishkeeping, What can I keep with shrimp? (pencilfish among fish that will almost certainly eat young shrimp; build the shrimp colony first; many fish medications unsafe for invertebrates); The Shrimp Farm, Red rili shrimp tank set-up and care (cherry-type Neocaridina: 65–85 °F, pH 6.2–8.0, GH 4–8). The shared water zones and the adult-shrimp assessment are our own reading.