Unicorn Catfish (Ageneiosus magoi)

Choose Ageneiosus magoi, the Unicorn Catfish of the Orinoco

Ageneiosus magoi is a long, active catfish from the Orinoco basin in Venezuela, sold in the UK as the Unicorn Catfish and sometimes simply as a driftwood catfish. It belongs to the Auchenipteridae, the family that fishkeepers call driftwood catfishes or woodcats because many of its members wedge themselves into sunken wood by day. This one is different: Planet Catfish notes that, unlike most of its relatives, it can be very active during the day, swimming in open water against the current.

It is a fish for an experienced keeper with a long aquarium. It grows to about 18 cm standard length, it is a carnivore that will swallow any fish that fits in its mouth, and it needs clean, moving water. In return it is one of the more striking and unusual catfish you can keep, with a bold spotted pattern and a remarkable breeding display.

Know the names before you buy

Recognise a true Ageneiosus magoi

The genus name comes from the Greek for "without a beard". Planet Catfish explains that Ageneiosus species do have barbels, but the maxillary pair is so short it is almost invisible, and the chin (mental) barbels are absent altogether. A fish with long, trailing whiskers is not an Ageneiosus. The head is long and slopes down to a broad, flattened snout, which gives the names Duck Catfish and Slopehead Catfish.

Planet Catfish describes the species as easily recognised by its black-and-white pattern, which varies a great deal between fish. Julian Dignall, who netted one in the Venezuelan llanos, describes white flanks with a half line of big black spots and golden fins. Wild fish often show yellow on the body and fins, and Planet Catfish notes that this fades after some time in an aquarium.

Check these features when your fish arrives

Select one fish and decide on a group

One purchase supplies one live Ageneiosus magoi in the standard size we receive. Sex is not specified, and it is hard to tell outside the breeding season. The price is for one fish. The gallery images are representative of the species; the pattern of spots differs from fish to fish, so yours will not match them exactly.

This species is peaceful towards fish too large to eat, and our sources describe keeping several together. Ginny Eckstein, whose 1994 article is summarised by Planet Catfish, bought a group of at least five and spawned them. Seriously Fish suggests four or more of the related A. marmoratus where space allows. A single fish also does well in a suitable large community.

Decide between one fish and a group

• One fish: the simplest choice for a large community of robust catfish and big characins.
• A group of four or five: the most natural display and the only way to see the breeding behaviour, but it needs a bigger tank and stronger filtration.
• Either way: plan the tank for the adult size before you order, not for the size that arrives.

Read our delivery and Live Arrival Guarantee policy before ordering, and have the aquarium running and tested before the fish arrives. More unusual species are in our rare and collector fish range.

Plan the aquarium around an 18 cm adult

Planet Catfish gives a maximum of 181 mm standard length, and FishBase gives the same 18.1 cm, measured without the tail fin, so a full-grown fish is noticeably longer overall. Some sellers quote 25–30 cm; we have found no source for that figure and use the published one.

None of our sources gives an aquarium size for this species. Seriously Fish recommends a base of at least 150 × 60 cm, about 540 litres, for Ageneiosus marmoratus, a close relative of the same size (185 mm), and warns that it is active, sometimes skittish and may injure itself by swimming into the glass. Planet Catfish asks for lots of swimming space for A. magoi. We therefore treat 150 × 60 cm as the minimum footprint for one fish and go larger for a group. Our tank volume calculator converts your tank's measurements into litres.

Run a four-step space check

1. Measure the length: this fish swims in open water, so length matters more than height. Aim for 150 cm or more.
2. Check the width: 60 cm front to back gives room to turn without hitting the glass.
3. Count the stock: every other large fish adds to the load. Our stocking calculator helps you add them up.
4. Fit a secure lid: OATA advises a fish-proof cover for large, active fish, which can be jumpy when first introduced.

Build open water with driftwood and a current

Planet Catfish asks for a few pieces of driftwood as hiding places, lots of swimming space and a strong current, noting that this species loves to swim against the flow and that a large pump is essential. Seriously Fish describes a similar set-up for A. marmoratus: soft sand, dim lighting, driftwood and roots, and plenty of open water. Keep the décor at the back and sides so the middle and front stay clear.

Use soft sand as the substrate; OATA recommends sand or fine gravel for all catfish to protect the barbels and underside. Secure every piece of wood and rock so a fast-moving fish cannot dislodge it, and protect the heater, as OATA advises for large fish.

Divide the tank by function

Set water values and hold them steady

Planet Catfish gives the water values for this species. FishBase gives none beyond "tropical". The OATA catfish guide gives broad values for catfish as a group, and Seriously Fish gives values for the related A. marmoratus. The target column uses the band where these overlap.

UK tap water ranges from soft to very hard depending on where you live, and much of it is above pH 7. Test your own water before the fish arrives. If it is hard and alkaline, mixing in reverse osmosis water brings it into range; our water matcher and water chemistry guide explain how. Change values slowly; a stable, slightly soft and slightly acidic tank is better than one that swings.

Separate habitat values from waste readings

Temperature, pH and hardness describe the habitat. Ammonia, nitrite and nitrate describe waste. OATA's targets are zero ammonia, zero nitrite and nitrate no more than 20 mg per litre above your tap water. A large carnivore produces a lot of waste, so test weekly and after every change to stocking or feeding.

Filter for a big eater and keep the water clean

Seriously Fish recommends efficient filtration, such as a large external canister or a sump, for A. marmoratus, and weekly water changes of 30–50%. It also warns that the fish is sensitive to organic pollution and should never go into a newly set-up tank. Plan the same for A. magoi. The filter return doubles as the current Planet Catfish asks for. Our guide to aquarium filtration covers mechanical, biological and chemical stages.

Follow a weekly maintenance sequence

1. Test ammonia, nitrite, nitrate, pH and temperature, and note the results.
2. Siphon uneaten food and waste from the sand, especially near the driftwood.
3. Change 30–50% of the water with dechlorinated water matched for temperature.
4. Rinse sponges in the removed tank water, never under the tap, as OATA advises, so the filter bacteria survive.
5. Check the heater guard, the lid and that every piece of wood is still secure.

Feed a measured carnivore meal

Planet Catfish calls this species a voracious feeder that eats anything that fits in its mouth, including large frozen foods and pellets, and warns that a diet of feeder goldfish is both one-sided and a disease risk. Ginny Eckstein's group adapted readily to prepared foods such as freeze-dried krill. Seriously Fish describes the related A. marmoratus as an obligate carnivore: new imports may at first take only live fish, but most can be weaned onto thawed whitebait or shellfish, and some onto carnivore pellets. It advises against mammal or bird meat.

We recommend thawed frozen foods and pellets rather than live feeder fish. OATA's rule for catfish is to feed what is eaten within a few minutes, once a day, and to remove leftovers.

Build one measured meal

Feed in the evening at first, close to the driftwood, and move feeding towards open water as the fish settles. If other catfish take most of the food, add a second feeding point.

Introduce it slowly to a mature aquarium

Many fish of this kind are wild-caught. OATA's advice is to switch off the aquarium lights, float the sealed bag for about 10 minutes so the temperatures match, then add small amounts of tank water over about 20 minutes before releasing the fish with as little bag water as possible. For sensitive or wild-caught fish, OATA describes a slower drip method. OATA also recommends that catfish are double-bagged because of their spines, so handle the bag with care. Our guide to acclimatising new fish walks through both methods.

Use a first-week checkpoint plan

Choose tank mates it cannot swallow

Planet Catfish puts it simply: this catfish ignores fish it cannot swallow. It suggests larger catfishes such as other auchenipterids, doradids and loricariids, and non-aggressive characins such as Metynnis. Seriously Fish lists similar company for A. marmoratus, adding eartheaters such as Geophagus. Our tank mates tool checks any combination you are considering.

Screen companions by mouth size first

Check each companion's adult size and water needs as well as its body size; they should all suit a long, flowing, slightly soft tank at 24–26°C. More ideas are in our catfish and plecos range, the South American catfish category and our centrepiece fish.

Watch for health signs and handle with care

OATA lists the signs of a healthy fish as clear eyes, undamaged fins, no ulcers or bumps, normal swimming and steady breathing. Changes in swimming, appearance or appetite are the earliest warnings. Like other driftwood catfishes, this species has strong spines in the dorsal and pectoral fins; use a large, soft net or a container and avoid lifting it by hand.

Pair each observation with an action

Understand its unusual breeding display

Driftwood catfishes breed by internal fertilisation. Planet Catfish and FishBase explain that the male's anal fin forms a mating organ, and that breeding males change shape: the dorsal-fin spine becomes longer, curved and serrated, and the short barbels become stiff, bony and toothed, so the male can clasp the female. After breeding these features shrink back. FishBase records that the type of spawning is still unknown.

Ginny Eckstein's 1994 account, summarised by Planet Catfish, describes her group developing these changes after about six months, within six to eight days, and an alpha male changing in 24 hours. Subordinate males flicked their dorsal spines fully forward and back, the display behind the name Unicorn Catfish. Spawning happened about twice a year and lasted around ten days; the fry were not reported, and Planet Catfish has no breeding report on file.

Answer Unicorn Catfish buying questions

What is a Unicorn Catfish?

It is Ageneiosus magoi, a slender, active catfish of the family Auchenipteridae (the driftwood catfishes or woodcats) from the Orinoco basin in Venezuela. Planet Catfish lists Unicorn Catfish, Duck Catfish and Slopehead Catfish as its common names.

How big does Ageneiosus magoi grow?

Planet Catfish and FishBase both give 181 mm, about 18 cm, standard length, which is measured without the tail fin. Some sellers quote 25–30 cm; we have not found a source for that and use the published figure.

What size aquarium does it need?

No source gives a figure for this species. Seriously Fish recommends a base of at least 150 × 60 cm for Ageneiosus marmoratus, a close relative of the same size, and Planet Catfish asks for plenty of swimming space and a strong current, so we plan on that footprint as a minimum.

What water does it need?

Planet Catfish gives 23–30°C and pH 6.4–7.0. We suggest holding 24–26°C and pH 6.5–7.0, inside every published range, with zero ammonia and nitrite and very low nitrate.

What does it eat?

It is a carnivore that eats anything that fits in its mouth. Aim for a diet of thawed frozen foods such as krill, mysis, prawn and pieces of whitebait, plus sinking carnivore pellets. Planet Catfish warns against a diet of feeder goldfish.

Will it eat my other fish?

It will eat any fish small enough to swallow and ignores fish it cannot swallow. Keep it only with fish that are clearly too big for its mouth, such as silver dollars, robust doradids and larger plecos.

Can I keep more than one?

Yes, if the tank is large enough. Ginny Eckstein kept and spawned a group of at least five, and Seriously Fish suggests four or more of the related A. marmoratus. One fish is also fine in a suitable community.

How do I tell males from females?

Outside the breeding season it is difficult; females are fuller in the body. Breeding males grow a longer, curved, serrated dorsal spine and stiff, toothed barbels, and their anal fin forms a mating organ. These changes fade after spawning.

Consult the care references

• Planet Catfish: Ageneiosus magoi: names, author and year, type locality, etymology, identification, sexing, distribution, water values, feeding, décor, compatibility and tank mates.
• Planet Catfish Catfish of the Month, March 2021: Ageneiosus magoi: the wild habitat in the Venezuelan llanos, wild colouring, and the 1994 aquarium breeding account by Ginny Eckstein.
• FishBase: Ageneiosus magoi: classification, maximum length (18.1 cm SL), habitat type, distribution, breeding biology and IUCN status.
• Seriously Fish: Ageneiosus marmoratus (related species): aquarium base, water values, filtration, water changes, diet and weaning for the similarly sized Ageneiosus marmoratus, used here only as a labelled comparison.
• OATA: How to look after freshwater catfish: UK guidance for catfish on water quality, sand, introduction, handling, feeding and health signs.
• OATA: How to look after wild caught freshwater fish: UK guidance on acclimatising sensitive or wild-caught fish, including drip acclimation.
• OATA: How to look after very large fish: UK guidance for large fish on filtration, secure décor and fish-proof covers.
• Tropical Fish Co delivery policy: current dispatch days and Live Arrival Guarantee terms.