Motatan pencil catfish

Where they come from

Motatan pencil catfish (Trichomycterus motatanensis) are one of those weird, cool little Andean-type fish that make you realize most "catfish" stereotypes are useless. They come from fast, cold-ish mountain streams where the water stays loaded with oxygen and the bottom is all rock, gravel, and leaf bits caught in crevices.

That background explains pretty much everything about them in aquariums: they hug the bottom, they hate stale water, and they act like little stream predators that would rather ambush than chase.

Setting up their tank

This is an advanced fish mostly because the tank has to be built around flow and oxygen. If you set them up like a typical community tank with gentle filtration and warm water, they usually fade out slowly and you will blame food or "mystery disease". Its almost always the environment.

• Tank size: bigger is easier. I would not do them in anything under a 20 long, and 30+ gallons makes stability and flow a lot simpler.
• Temperature: aim cool to mid range. Think low 70s F (around 21-23 C) as a sweet spot. Avoid keeping them in warm tropical temps long term.
• Flow and oxygen: strong filtration plus actual current. A canister with a spray bar, or a powerhead pointed along the length of the tank, makes a huge difference.
• Substrate: smooth gravel, small river stones, and sand patches work. Skip sharp stuff - they like to wedge themselves into places.
• Hiding spots: piles of rounded rock, slate caves, and lots of tight gaps. Leaf litter in calmer corners is great too.
• Lighting: they do not care, but you will see them more with subdued light and shaded areas.
• Water quality: clean and consistent. They do not tolerate "old" water the way some hardy catfish do.

I like to build a "river lane" down the middle with stronger current, then create quieter pockets behind rocks and wood. That gives them choices. They will often sit where food drifts by, not necessarily where the flow is strongest.

What to feed them

These are not algae grazers. Mine took to meaty foods fast, but they rarely dash to the surface like a cory. Think of them as micro-predators that pick and pounce.

• Staples: sinking carnivore pellets, micro wafers, and gel foods that sink quickly.
• Frozen: bloodworms, blackworms, daphnia, chopped mysis, and brine shrimp (brine is more of a treat than a main food).
• Live (if you can): blackworms and small earthworm pieces get the best feeding response in my experience.
• How to feed: small amounts, more than once. They do better with frequent bite-sized feedings than one big dump.

Watch their bellies. A healthy Motatan pencil catfish should look sleek but not pinched. If you only ever see the tankmates eating, you will end up with a skinny fish hiding all the time.

How they behave and who they get along with

They are secretive, bottom-focused, and surprisingly bold once they feel secure. Most of the time you will see them perched on rock edges or tucked into cracks with just the head out.

Aggression is usually subtle: little shoves and "my cave" standoffs. In cramped tanks, one can dominate the best hideouts and the others just vanish (not dead, just wedged somewhere you cannot see). More rockwork and more hiding holes fixes a lot of that.

• Good tankmates: cool-water, current-loving fish that will not bully the bottom - small to medium characins from cooler setups, some danios, and other stream species with similar temp needs.
• Be careful with: corydoras and other bottom feeders. Not because of constant fighting, but because they compete for the same food and space.
• Avoid: big aggressive cichlids, fin-nippers that harass anything that sits still, and warm-water fish that push temps into the upper 70s/80s F.
• Shrimp/snails: small shrimp can disappear. Adult snails are usually fine.

Breeding tips

Breeding them in home tanks is not common, but you can stack the odds by copying seasonal stream changes. I have seen the most courtship-y behavior after heavy water changes with slightly cooler water and a noticeable bump in current.

• Give them a "spawning maze": tight caves, stacked stones, and crevices that feel secure. Think narrow entrances.
• Condition them hard on meaty foods for a few weeks.
• Do a series of larger water changes (30-50%) with water a couple degrees cooler, and increase flow for a day or two.
• If you suspect eggs, keep the tank calm and well-oxygenated. Many pencil catfish are not great parents, so eggs and tiny fry may need separation if you actually want numbers.

Common problems to watch for

Most issues with this species look like "mystery wasting" but have pretty normal causes: warm water, low oxygen, not getting enough food, or getting outcompeted at feeding time.

• Rapid breathing, hanging in the open: usually oxygen/flow/temperature problems. Fix the environment first.
• Skinny belly, hiding constantly: not eating enough or getting bullied off food. Feed at night, use targeted sinking foods, reduce competition.
• Scrapes and missing barbels: rough decor or getting shoved into sharp rock gaps. Use rounded stones and sand patches.
• Sudden losses after a filter slowdown: they are sensitive to drops in oxygen. Keep intakes clean and have backup aeration if your area gets outages.
• Ich and other parasites: they can get it like any fish, but treat gently and focus on water quality. They do not appreciate overheated "ich cures" because they are a cooler-water fish.

If you keep the water cool, moving, and clean, and you make sure food actually reaches them, they are fascinating little oddballs. The hard part is resisting the temptation to treat them like a standard bottom-dweller.