Ruitoque pencil catfish

Where they come from

Ruitoque pencil catfish (Trichomycterus ruitoquensis) come from Colombia, from cold, fast-moving Andean foothill streams. Think shallow runs, lots of rock, leaf bits caught in crevices, and water that is moving all the time.

That origin story explains basically everything about them: they like high oxygen, they hate dirty water, and they feel safest wedged under something with current washing over them.

Setting up their tank

This is an expert fish because you are really keeping the water and flow right more than you are keeping the fish. A generic planted community tank at 78F with gentle filtration is usually a slow-motion failure.

I have had the best luck treating them like a small stream biotope: cooler water, hard surfaces, tons of hiding cracks, and serious oxygenation.

• Tank size: 20 long works for a small group, bigger is easier because parameters swing less
• Temperature: aim cool (roughly high 60s to low 70s F). If your room runs warm, plan for a fan or chiller
• Flow and oxygen: strong turnover, a powerhead pointed along the length, and/or a spray bar rippling the surface
• Filtration: oversized bio filtration, plus mechanical to catch sand and mulm before it rots
• Substrate: sand or very fine gravel with lots of smooth rocks. Skip sharp gravel - they will scrape themselves
• Hardscape: stacks of rounded stones, small caves, slate piles, and tight gaps. Give them places to wedge into
• Light: dim to moderate. They are much bolder in lower light
• Plants: optional. If you use them, pick stuff that tolerates cooler, higher-flow tanks (Anubias, Java fern, mosses)

Cover the intake. They are slender and curious, and they will investigate crevices. A prefilter sponge saves you from a really stupid loss.

What to feed them

They are micro-predators. In my tanks they ignored flakes and most pellets at first and went straight for anything meaty that moves or smells like it should.

• Best staples: live or frozen blackworms, tubifex (from a trusted source), bloodworms, daphnia, cyclops
• Also good: chopped earthworms, small pieces of raw shrimp/fish (sparingly), high-quality sinking micro-pellets once they recognize them as food
• How to feed: target feed with a pipette or turkey baster so food gets into their rock piles before midwater fish steal it
• Schedule: small meals daily or every other day. They do better with frequent small feedings than big dumps

How they behave and who they get along with

Most of the time they are secretive little needles that vanish into rockwork. Then you catch a quick dart, a wiggle, and they are gone again. In groups they are less spooky, but they still want lots of cover.

They are not a peaceful community fish in the usual sense. They are not out to bully everything, but they are built to grab tiny animals, and they will test anything that looks bite-sized.

• Good tankmates: cool-water, current-loving fish that stay midwater and are not tiny enough to be food (think larger danios or similar stream fish)
• Risky tankmates: shrimp, fry, tiny tetras, very small rasboras - I would assume they will get eaten eventually
• Bad tankmates: slow long-finned fish, warm-water fish, and aggressive bottom fish that will claim the same cracks
• With their own kind: doable if you give lots of hides and break line-of-sight with rocks. Expect some shoving for favorite slots

Breeding tips

Breeding Trichomycterus in aquariums is not common, and with this species it is more of a long-game project than a weekend plan. If you want to try, think like the stream: seasonal cues, lots of oxygen, and safe crevices for eggs.

• Start with a group so you are not guessing sex (they are not obviously dimorphic to most hobbyists)
• Keep them very well fed on live/frozen foods for a few weeks
• Do cool water changes with strong flow to mimic rain events
• Provide multiple tight caves and rock stacks where eggs could be placed out of sight
• If you find eggs, move them with the rock if possible (less handling), and keep aeration high

Common problems to watch for

Most losses I have seen with pencil catfish come down to three things: not enough oxygen/flow, chronic low-level ammonia/nitrite from a young or dirty filter, or slow starvation because tankmates eat everything first.

• Gasping or hanging in high-flow spots: usually oxygen is low or temperature is too warm for the oxygen you have
• Skin damage or red sores: often from sharp substrate, rough rock, or being pinned by a stronger bottom fish
• Sudden deaths after a filter clean: you may have stripped too much bio media or stirred a bunch of waste out of the substrate
• Getting thin while still active: food competition or feeding the wrong size/type
• White stringy poop and weight loss: internal parasites are not rare in wild fish - quarantine and be ready to treat

Quarantine is worth the hassle with this species. A bare-bottom tank with a cycled sponge filter, a few PVC elbows, and heavy aeration lets you observe feeding and poop, which tells you a lot. Once they are eating like pigs and holding weight, they handle the display tank transition way better.