Pencil catfish
Trichomycterus zonatus
The Pencil catfish features a slender, elongated body with a distinctive yellowish-brown coloration and prominent dark stripes along its sides.
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About the Pencil catfish
A tiny riffle-lover from southeastern Brazil, this little pencil catfish spends its days nosing through pebbles for insect snacks. It wears irregular blotches that line up into bars along the body, which looks awesome against a rocky stream setup. Give it cool, fast, super-oxygenated water and it will settle in and show off its daytime foraging routine.
Quick Facts
Size
6.2 cm
Temperament
Peaceful
Difficulty
Intermediate
Min Tank Size
20 gallons
Lifespan
3-6 years
Origin
South America - southeastern Brazil (Santa Catarina to Sao Paulo)
Diet
Invertivore - small live and frozen foods, sinking micro-pellets
Water Parameters
16-23°C
6-7.5
1-8 dGH
Need a heater for this species?
This species needs 16-23°C in a 20 gallon tank. Use our heater calculator to find the right wattage.
Calculate heater sizeCare Notes
- Set up a river-style tank: 20-gallon long or bigger with soft sand, rounded stones, snug caves, and a tight lid. Push strong current and oxygen with a canister plus powerhead or spray bar.
- Keep it cool and clean: 68-74 F (20-23 C), pH 6.2-7.2, 2-10 dGH. Do 30-50% weekly changes and avoid heat spikes above 76 F.
- They hunt tiny stuff on the bottom; give live or frozen bloodworms, blackworms, mosquito larvae, chopped earthworm, and small sinking carnivore pellets. Feed at lights-out or use a feeding tube so faster fish dont steal it.
- Pick calm midwater fish that like flow and wont bulldoze the bottom, like white clouds, small danios, or mellow tetras. Skip cichlids, big plecos and loaches, crayfish, and any food hogs.
- Keep 4-6 together; singles hide and often miss meals. In a group they come out more and forage properly.
- They are skinny escape artists and can get into filters; put sponge over intakes and seal lid and HOB gaps. Use sand, not sharp gravel, to save their barbels.
- Captive spawns are rare, but if you try, give flat stones or tight tubes in strong flow and cool the tank a couple degrees with big water changes while feeding heavy live foods. If eggs show under a stone, move it to a hatching box with strong aeration; start fry on infusoria then baby brine.
- Wild-caught fish often bring internal worms, so quarantine and deworm with praziquantel or levamisole. Heavy breathing or surface hanging means your oxygen is low and you need more flow and air right away.
Compatibility
Good Tankmates
- Small, fast schooling fish that enjoy cool, well-oxygenated flow (white clouds, zebra danios), so everyone zips around and nobody bothers the catfish
- Peaceful midwater tetras that handle current (black neons, pristella) kept in good-sized groups so they mind their own business
- Cherry barbs or other gentle barbs in groups - not the nippy kinds, and they do fine in a river-style setup
- Corydoras from the cooler end (paleatus, aeneus) that forage without getting territorial, plus plenty of hides for everyone
- Hillstream loaches and similar current-loving grazers that ignore them and thrive in the same high-oxygen conditions
- Small bristlenose or whiptail plecos, provided there are multiple caves so nobody argues over the best hide
Avoid
- Large or territorial cichlids and other predators that will view a slender catfish as food (anything that can fit them in the mouth)
- Nippy, pushy fish that harass bottom dwellers (tiger barbs, serpae tetras, redtail sharks)
- Very slow, long-finned fish that dislike cool, fast flow (bettas, fancy guppies, angelfish) - they get stressed in this setup
- Tiny nano fish and shrimp colonies if you want babies to survive - these catfish will snack on fry and shrimplets after lights out
Where they come from
Pencil catfish in the Trichomycterus group, including T. zonatus, are stream fish from northwestern South America. Think clear, cool foothill creeks with a rocky bottom, brisk flow, and loads of dissolved oxygen. They spend daylight tucked under stones and wood, then zip out to pick at insect larvae in the current.
You will see a mix of Trichomycterus species sold as pencil catfish. Care is very similar across the group, but exact appearance can vary.
Setting up their tank
Give them a long tank over a tall one. A 24-30 inch footprint works for a small group, with lots of cover. They are current-lovers, so plan filtration and flow like you would for hillstream fish.
- Substrate: fine sand or smooth small gravel so they can nose around without tearing barbels
- Hardscape: tight rock piles, rounded cobbles, branching wood, and leaf litter for extra hideouts
- Flow and oxygen: a canister or HOB plus a powerhead or river manifold; point outlets to ripple the surface
- Lighting: on the dim side; floating plants or hardscape shadows help
- Lid: tight fitting - they are sneaky jumpers
- Plants: tough rhizomes like Anubias or Bolbitis tied to wood and rocks do well in flow
Water that is clean and cool suits them best. Aim for pH 6.2-7.4, soft to moderate hardness, temperature 18-23 C (64-73 F). Keep nitrate low and oxygen high. Weekly 30-50% water changes keep them perky.
Heat is the enemy. Above 24 C they get sluggish and start gasping if oxygen drops. Use a fan or chiller in summer and keep strong surface agitation.
What to feed them
They are micro-predators that like small, moving foods. They will take prepared foods once they settle, but you get better condition if you mix in live or frozen.
- Live or frozen: blackworms, bloodworms, daphnia, mosquito larvae, baby brine shrimp, chopped earthworm
- Prepared: quality sinking micro pellets, small carnivore pellets, Repashy gel foods pressed into crevices
- Supplement: occasional finely chopped prawn or mussel
Feed at lights-out or just after. Target feed with a turkey baster or pipette into their hidey holes so midwater fish do not steal everything. Pre-soak pellets so they sink fast.
Avoid relying on flakes and wafers only. They often ignore food sitting out in the open, and leftovers rot quickly in rock piles.
How they behave and who they get along with
Quiet, crepuscular, and a bit skittish at first. They wedge into tight spots during the day and make quick dashes into the current to grab food. Not aggressive, but very food-focused once comfortable.
- Group size: 4-6 works well. They are not schooling, but having more than one spreads attention and makes them bolder.
- Good companions: small, calm fish that like cooler, clean water - peaceful tetras, pencilfish, cold-tolerant rasboras, hatchetfish, and non-pushy hillstream loaches.
- Use caution with: other bottom dwellers that compete hard for hides and food, like boisterous Corydoras or large loaches.
- Skip: cichlids, big barbs, predatory characins, or anything that will harass or outcompete them.
Add a small group of calm midwater fish as dithers. Seeing other fish out in the open helps pencil cats feel safer about venturing out.
Breeding tips
Spawning in home tanks is rare and not well documented for T. zonatus, but you can try a stream-style species tank. Use stacks of smooth stones with narrow gaps, leaf litter, and pieces of PVC or bamboo split lengthwise as tight caves.
- Condition a small group heavily with live and frozen foods.
- Run strong, steady flow and keep temps around 19-21 C.
- Simulate rainy season with larger cool water changes and a slight drop in TDS.
- Watch for adults getting extra active at dusk and nosing into crevices.
- If you spot eggs, pull the stack or move adults. Try a small powerhead with a sponge guard for gentle circulation over the site.
- For fry, start with infusoria-rich leaf litter, then microworms and newly hatched brine shrimp.
Sexing is tricky. Males are often a bit slimmer with slightly longer pectoral fin rays, but this varies by species. Share your results if you crack it.
Common problems to watch for
- Low oxygen and heat stress: rapid gilling, hanging at the surface, or piling in front of the filter output. Add flow and drop the temp.
- Starving in community tanks: they miss meals if food never reaches the bottom. Target feed and watch body condition from above.
- Barbel wear and fungal nicks: sharp gravel and dirty substrate cause issues. Use smooth sand and keep up on siphoning between rocks.
- Scrapes from tight gaps: build hides with smooth stones and test gaps with a credit card width. If you cannot slide the card, it is too tight.
- Medication sensitivity: like many scaleless catfish, they react badly to copper and full doses of formalin or malachite green. If you have to treat, go half-dose, raise aeration, and observe closely.
- Misidentification: different Trichomycterus can show up mixed. Do not assume yours will behave exactly like photos online.
They jump. Any opening around filter pipes or cables is an exit. Tape gaps or use mesh to cover cutouts.
Day-to-day success is all about clean, cool, oxygen-rich water and making sure food actually reaches them. Do that, and these little stream cats behave naturally and stick around for years.
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