Colombian shark catfish

1) Where they come from

Colombian shark catfish (Ariopsis seemanni) come from the Pacific side of Central America—think river mouths, mangroves, and coastal lagoons. They’re not “river catfish” the way a lot of shops sell them. They’re built for that in-between life where fresh and salt mix, and they act like it.

2) Setting up their tank

Plan the tank around their adult size and their speed. These are active, nervous, open-water cruisers that spook easily and hit the glass hard if they feel boxed in. The best thing you can give them is length and clear swimming room.

• Tank size: I’d start at 75g for a small group of juveniles, but adults really want 125g+ (6-foot tank is where they start looking “right”).
• Group size: keep 3+ if you can. Singles tend to be jumpy and hide-y; groups settle down and school more.
• Filtration: strong, over-sized filtration with lots of oxygenation. They’re messy eaters and they’re active.
• Flow: moderate flow is fine. They’ll use it, but don’t make it a washing machine.
• Substrate/decor: sand or smooth gravel, rounded rocks, and driftwood. Skip sharp decor—these guys can scrape themselves during panicked dashes.

For brackish, I mix marine salt (not aquarium “tonic salt”) and aim for a steady specific gravity rather than chasing numbers every day. Juveniles can handle the lower end, but adults generally look better and act more confident with more salt in the mix.

• Salinity target: think light-to-medium brackish (many keep them around SG ~1.005–1.015 depending on age and tankmates). Pick a target and keep it stable.
• Measure with a refractometer or a decent hydrometer—don’t guess.
• Top off evaporation with fresh water, not saltwater, or the salinity creeps up.

3) What to feed them

They eat like little sharks—enthusiastic, competitive, and not picky once settled. The trick is giving them meaty foods without turning the tank into a nitrate factory.

• Staples: quality sinking carnivore pellets and wafers (they learn pellets fast and it keeps nutrition consistent).
• Frozen: shrimp, mysis, krill, chopped clam, squid, and fish flesh as an occasional treat.
• Live: not needed. If you use live foods, quarantine them—these cats don’t need extra parasites.

I feed smaller amounts 1–2 times a day and watch the belly line. They’ll beg like they’re starving, but they put on weight easily in captivity. Big messy feedings are the quickest way to sour water with this species.

4) Behavior and tankmates

They’re schooling catfish with a “bold when comfortable, spooky when stressed” personality. In a roomy tank with a group, they cruise midwater and look fantastic. In cramped tanks, they ping-pong and hide, and that’s where injuries start.

• Temperament: generally peaceful, but anything small enough to fit in their mouth is food sooner or later.
• Activity: mostly active all day once settled, especially at feeding time.
• Social: noticeably calmer in groups.

Tankmates need to match the vibe: brackish-tolerant, not bitey, and big enough not to be eaten. Also avoid fin-nippers—these catfish don’t enjoy being harassed, and they’ll stress out fast.

• Good fits (depending on salinity): monos, scats, larger brackish gobies, knight gobies (with size awareness), some brackish puffers with caution, and other similarly sized brackish fish that aren’t aggressive.
• Avoid: tiny fish, slow long-finned fish, and hard-core bullies that chase or nip.

5) Breeding tips

Breeding them at home is rare. They’re marine/brackish catfish with mouthbrooding behavior (the male carries the eggs/fry), and getting a compatible pair plus the right space and conditions is a tall order. Most hobbyists keep them for their look and behavior, not as a breeding project.

6) Common problems to watch for

Most issues I’ve seen come from three things: keeping them in freshwater long-term, keeping them in too small a tank, or letting water quality slide because they’re big eaters.

• Freshwater fade-out: they may look okay for months, then get thin, stressed, and more prone to infections. Long-term brackish tends to flip that around.
• Glass-banging injuries: scraped noses, torn fins, missing barbels—usually from spooking in tight tanks or with aggressive tankmates.
• Fin rot/skin infections: often tied to dirty water and stress. These fish show problems fast when conditions drift.
• Ich/parasites: can happen, especially after new additions. Treat carefully in brackish—some meds don’t play nicely with salt and scaleless fish.
• Feeding bloat/constipation: less common than in some species, but it happens with huge meals of rich food.