Flathead long-whiskered catfish
Megalonema platycephalum
The Flathead long-whiskered catfish features a broad, flat head, long sensory whiskers, and a pale brown to yellow-green body with dark mottling.
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About the Flathead long-whiskered catfish
This is a real-deal South American pimelodid catfish that stays in that "big but not monster" range - around a foot long - with that wide, bulldog-ish head and long whiskers. Its natural diet includes insect larvae and even fish scales, so it has that sneaky bottom-predator vibe and will absolutely inhale meaty foods once it settles in. The big "gotcha" is that it sometimes shows up mislabeled in shops (even as other catfish species), so you want to buy it assuming you'll be housing a 12-inch predator.
Also known as
Quick Facts
Size
30 cm (12 inches) TL
Temperament
Semi-aggressive
Difficulty
Intermediate
Min Tank Size
100 gallons
Lifespan
10-15 years
Origin
South America
Diet
Carnivore/predator - sinking meaty pellets, frozen foods (shrimp, fish, worms), occasional live foods
Water Parameters
22-27°C
6-7.2
2-15 dGH
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Calculate heater sizeCare Notes
- Give it floor space, not height - a 55+ gallon with a big sandy area, driftwood, and a couple tight caves works way better than a tall tank.
- They are whisker-first hunters, so skip sharp gravel and rough rock; torn barbels happen fast and they get shy and stop cruising.
- Keep the water warm-ish and stable: about 75-80F, pH around 6.5-7.5, and keep nitrates low with regular water changes because they hate dirty bottoms.
- Feed after lights out since they are more confident then; sinking carnivore pellets, frozen bloodworms, shrimp, and chopped earthworms get a strong feeding response.
- Do not rely on flake or floating foods - they will miss most of it and slowly lose weight even though you think you are feeding.
- Tankmates should be calm and too big to swallow: medium characins, larger rasboras, peaceful cichlids, and other non-nippy bottom fish; avoid fin-nippers and anything small enough to become a midnight snack.
- Watch for skinny belly and damaged whiskers as your early warning signs; both usually point to not enough sinking food, too much competition at feeding, or a rough/dirty substrate.
Compatibility
Good Tankmates
- Medium to large characins that are too big to fit in its mouth - think silver dollars or big, deep-bodied tetras (Congo tetra sized and up). They cruise the midwater and usually ignore the catfish, and the cat mostly minds its own business if it is well fed.
- Sturdy cichlids that are not psycho-territorial - severums, keyholes, smaller geophagus types. As long as everyone has space and you have lots of wood/cover, they generally coexist well together.
- Bigger peaceful catfish as neighbors - pictus-sized catfish may be too small, but larger doradids (talking catfish) or similarly sized calm pimelodids can coexist well if the tank is spacious and multiple hiding places are available.
- Robust midwater schooling fish that can handle a semi-aggressive vibe - larger rainbowfish or larger barbs (like tinfoil barbs) if your tank is spacious. They are fast and not easily bullied, and they do not camp in the catfish's favorite spots.
- Armored bottom fish that keep to themselves - larger plecos (common/sailfin types) or big Hypostomus/Pterygoplichthys. They are tough, have their own attitude, and the flathead long-whiskered usually leaves them alone when everyone has hiding places.
- Other large, calm oddballs that are not bitey and not snack-sized - larger knifefish or big headstanders can be OK in a big setup, any species that is confident and does not linger at the bottom where the catfish establishes territory may be suitable.
Avoid
- Small community fish that fit in its mouth - neon-sized tetras, danios, small livebearers. This catfish is a nocturnal hunter, and over time, you may observe a decrease in your fish population.
- Slow, fancy-finned fish - angelfish with long fins, fancy guppies, anything that drifts and sleeps low. They get stressed, may get fin-nipped, and they are easy targets at lights-out.
- Super aggressive or territorial bruisers - jaguar cichlids, red devils, big nasty oscars in cramped tanks. They will pick fights, hog caves, and this can result in significant stress and injury to the fish.
- Delicate bottom dwellers and little catfish - corydoras, small synodontis, juvenile plecos. They compete for the same floor space and caves, and the flathead long-whiskered can bully them or outright eat them once it gets size on them.
Where they come from
Megalonema platycephalum is a South American river catfish. You see it tied to the big, warm lowland systems (think broad rivers and floodplains) where the water is usually tannin-stained, full of leaf litter, and the fish spend a lot of time hugging the bottom and structure.
The whole "long-whiskered" thing is real. Those barbels are built for feeling their way around in dim water, which tells you a lot about how to set them up at home.
Setting up their tank
Give this fish floor space first, not height. They are bottom cruisers, and they get stressed if they feel exposed. If you set up a bright, bare tank, you will mostly own an empty aquarium and a nervous catfish.
- Tank size: I would not bother under 55 gallons, and 75+ is a much nicer long-term home because they need room to patrol the bottom.
- Substrate: smooth sand is my pick. Fine gravel can work, but sand is easier on the barbels and encourages natural rooting around.
- Hiding spots: driftwood, root tangles, and a couple of caves (PVC works if you hide it). Provide more than one so it can choose.
- Lighting: keep it subdued. Floating plants or tannins from wood/leaf litter help a lot.
- Flow and filtration: decent turnover with steady current is good, but avoid blasting the bottom. They appreciate clean, oxygen-rich water.
If you want to actually see your fish, set the tank up with shade and cover, then feed after lights out. Mine learned the schedule and started showing up earlier and earlier at dusk.
Water-wise, aim for typical tropical South American community parameters: warm, soft-to-medium water, stable pH, and low nitrate. Stability beats chasing numbers. Do regular water changes and keep the bottom from turning into a mulm swamp.
What to feed them
They eat like a catfish: meaty, sinking foods, mostly at night. Mine ignored flakes completely but went straight for anything that hit the bottom and smelled like food.
- Staples: quality sinking carnivore pellets or wafers (not the cheap starchy stuff).
- Frozen foods: bloodworms, mysis, chopped krill, brine shrimp, and especially earthworm pieces.
- Occasional: live blackworms or live earthworms if you can get them clean and safe.
- Skip as a habit: feeder fish (disease risk and they can make your catfish picky).
They will absolutely hoover food into their mouth with the substrate. If your sand is coarse or dirty, that is a fast track to irritated barbels and infections.
Feed small portions more often rather than one huge dump. Big catfish meals can foul the tank fast, and these guys are happy to keep eating if you keep offering.
How they behave and who they get along with
They are generally chill, a little shy, and most active in low light. The main "attitude" issue is size-based: if it fits in the mouth, it might become a midnight snack.
- Good tankmates: medium-to-large peaceful fish that stay midwater (bigger tetras, silver dollars, many larger cichlids that are not hyper-aggressive, peaceful characins).
- Use caution: other bottom dwellers (they may compete for caves and food), slow fish that sleep on the bottom, and anything tiny.
- Avoid: nano fish, delicate long-finned fish that rest low, and super-aggressive cichlids that will claim every cave.
They are not usually a fin-nipper or a bully. Most problems I have seen were either food competition (they get outcompeted) or predation on small fish at night.
One more thing: they can spook hard. A tight-fitting lid matters. If something startles them, they go from statue to torpedo in a heartbeat.
Breeding tips
Breeding Megalonema platycephalum in home aquariums is not something you see often. Sexing is not obvious, and most imports are just kept as single specimens or in mixed communities where spawning behavior never really gets going.
If you want to take a swing at it, think like a river fish: heavier feeding for conditioning, lots of cover, and a seasonal "rainy period" simulation with cooler, larger water changes and a bump in flow and oxygen. Even then, I would treat it as a long shot and enjoy them for what they are.
Common problems to watch for
- Barbel wear or infection: usually from sharp gravel, dirty substrate, or constant digging through waste. Sand and a clean bottom fix most of it.
- Skin scrapes: they wedge into tight spots. Give them caves that fit the whole body, not just the head.
- Starving in a busy community: they are polite eaters. If faster fish steal everything, target feed with tongs or drop food right at their cave after lights out.
- Bloat/constipation: too much dry food and not enough variety. Mix in frozen foods and do not overfeed pellets.
- Ich and other parasites on new imports: quarantine if you can. Wild-caught fish can arrive stressed and sensitive.
Catfish are often touchy with medications, especially strong doses and some copper-based treatments. If you have to medicate, research the drug first and start lighter, with extra aeration.
The biggest success factor with this species is simple: a calm, shady tank with clean sand and predictable feeding. Do that, and you will get a confident fish that actually comes out instead of hiding forever.
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