L025 Scarlet Cactus Pleco (Pseudacanthicus pirarara)

Meet the L025 Scarlet Cactus Pleco

The L025 Scarlet Cactus Pleco (Pseudacanthicus pirarara) is one of the most dramatic suckermouth catfish in the hobby and one of the largest. Its dark brown body is covered in black spots and studded with rows of pointed odontodes, the tooth-like bristles that give cactus plecos their name, while the dorsal fin, tail and the edges of the other fins glow red to scarlet. It comes from the lower and middle Rio Xingu in Brazil and its tributaries, the Rio Bacajá and the Rio Iriri.

It was traded for decades as L025 before Chamon and Sousa described it scientifically in 2016 as Pseudacanthicus pirarara. Planet Catfish explains the name: local fishermen call it "assacu-pirarara", where pirarara refers to the reddish fins (it is also the Brazilian name of the red tail catfish) and assacu is a rainforest tree whose bark is covered in conical spines. This is a fish for an experienced keeper with a very large aquarium.

Check the names on the label

Planet Catfish places Pseudacanthicus in the Acanthicus group of plecos, which share rows of keels of pointed odontodes along the sides of the body, eight or more dorsal-fin rays and enlarged odontodes along the edge of the snout. Pseudacanthicus also has a narrow upper jaw with a small number of long, curved teeth. Compared with L024, L025 shows considerably more red in the fins and more pronounced black spots, and its eyes give it a hooded, almost "evil" look. Browse its relatives in our Acanthicus plecos range, every coded catfish in our L-number plecos category, the wider South American catfish range, our centrepiece fish or the full catfish and plecos collection.

Know what one purchase supplies

One purchase supplies one live L025 Scarlet Cactus Pleco at the standard size offered on this listing. Whatever its length on arrival, it is the same species that reaches 40–45 cm, so make every decision about the aquarium for the adult fish.

Sex is not specified. Planet Catfish describes mature males as carrying considerably more odontodes on most fin rays, especially the pectoral fins, while females fill out much more than the slender males. These differences only show in large, mature fish.

The photographs show the species, not the individual you will receive. The amount of red in the fins, the density of the black spots and the body shade vary between fish and with mood and lighting, so expect some difference from the pictures.

Plan from the adult, not the sale size

• Adult length: Planet Catfish gives 450 mm standard length (body length without the tail); FishBase gives 40.5 cm total length and a weight of up to 950 g.
• Aquarium: very large; at least the 180 × 60 cm base Seriously Fish asks for the smaller L114, and more for an adult.
• Temperature: Planet Catfish gives 24–26°C.
• Diet: meaty foods with some vegetables.
• Social plan: the only large bottom dweller in the tank.

Before ordering, read our delivery and Live Arrival Guarantee information and have the aquarium running and mature, so the fish goes straight into stable water.

Plan a tank for a 40–45 cm adult

No source publishes a minimum aquarium size for L025 itself, so we work from its relatives and from keepers. Seriously Fish asks for a base of at least 180 × 60 cm, about 648 litres, for the L114 leopard cactus pleco, which grows to only 250 mm. OATA's guidance on very large fish says such species need an exceptionally large aquarium, often well over 500 litres, and that an off-the-shelf tank is unlikely to be big enough in the long term. The keeper who spawned L025 for Planet Catfish kept three adults of 30–35 cm standard length in a 1,600-litre aquarium.

Take 180 × 60 cm as the absolute floor while the fish is young, and plan a larger tank for the adult. As with all big plecos, floor area matters more than height: this fish spends its life on the bottom and in caves, so a long, deep tank serves it far better than a tall one of similar volume.

Use a three-step space check

1. Measure the base: at least 180 cm long and 60 cm from front to back, with room to grow into more.
2. Claim one cave: give it a cave or pipe longer than the adult fish, well away from any other bottom dweller's retreat.
3. Count the waste: size the filtration for a 40–45 cm carnivore, not the youngster you receive.

Our tank volume calculator turns your tank's dimensions into litres, and our stocking calculator helps you see how much of a tank's capacity one large pleco uses before you add anything else.

Build robust cover and a river floor

Planet Catfish describes L025 as fairly reclusive and says it needs robust decoration and cover to hide in. It adds a warning: make sure no other fish tries to dispute ownership of that cover, because this pleco will fight for its territory. Seriously Fish recommends a flowing-river layout for its relative L114: variably sized rocks, sand and fine gravel with some water-worn boulders, plus driftwood branches and terracotta pipes arranged into nooks and shaded spots with broken lines of sight.

Divide the tank by function

OATA warns that large fish can knock over décor, so bed every rock and cave directly on the glass before adding sand and check that nothing can topple. Fit a secure, fish-proof cover, as OATA advises for very large fish, which can be jumpy when they arrive in a new tank.

Set water values within the published range

Planet Catfish gives 24–26°C and pH 6.0–7.4 for L025, and stresses clear, well-oxygenated water. The sources are thin here and do not fully agree: the keeper who spawned it reports a tank of around 28°C, a temporary drop to 24°C during the water changes that seem to have triggered spawning, and fry that only fed well at 28°C. No hardness range is published for L025; Seriously Fish gives 1–15 dGH and 24–30°C for its relative L114. We suggest staying within 24–28°C, the span those reports cover, and holding the temperature steady.

Separate habitat values from waste readings

The waste limits come from OATA's catfish care sheet. In a tank with a large carnivore they are the readings that go wrong first, long before pH or hardness drift.

UK tap water varies a great deal from region to region. Soft and moderately hard supplies suit this fish well, while very hard water in parts of southern and eastern England may need blending with reverse-osmosis water. Your water company publishes the hardness for your postcode. Always treat tap water with a conditioner that removes chlorine and chloramine. Our water matcher compares your readings with this fish's range, and our water chemistry guide explains each reading.

Filter for a big, messy carnivore

Planet Catfish is blunt: Pseudacanthicus are big, messy carnivores and, like all large plecos, produce vast amounts of waste, so housing one with other large fish would need monumental filtration. OATA agrees that very large fish may need several large aquarium filters or even a pond filter to deal with the solid waste. For the 648-litre tank it recommends for L114, Seriously Fish suggests two filters each rated at roughly 1,295–1,620 litres per hour, four to five turnovers an hour in total, and about 150–225 W of heating across four heaters, assuming a room near 20°C.

Add strong water movement and aeration: Planet Catfish asks for clear, well-oxygenated water, and the keeper who spawned it ran a Xingu river tank. OATA advises protecting heaters from damage in tanks with large fish, so fit guards or place heaters in a sump.

Follow a weekly maintenance sequence

1. Test ammonia, nitrite and nitrate before you start.
2. Change at least 25% of the water every week, as OATA recommends; with a large carnivore, more is better.
3. Treat the new water with a conditioner and match its temperature before adding it.
4. Siphon uneaten food and droppings, especially around the cave after meaty meals.
5. Clean filter pre-filters often, because solid waste builds up quickly.
6. Rinse filter media in removed tank water, never under the tap.

The published spawning began after a nitrate spike forced three 400-litre water changes in three days, a reminder of how quickly waste builds up in a big-fish tank and how well this species responds to large volumes of fresh water.

Feed a meaty diet with some vegetables

Planet Catfish describes L025 as a carnivore, although not a predator. It names prawns and chopped mussel as favourites that promote good growth, and says some vegetable food should also be offered to balance the diet. Seriously Fish's advice for L114 fills in the detail: sinking dried foods, frozen daphnia, mosquito larvae and bloodworm, prawn or shrimp, plus some fresh fruit and parboiled potato, or a home-made, gelatine-bound mix of seafood, vegetables and Spirulina.

Build one measured meal

• Main portion: sinking carnivore pellets or tablets the fish clears within a few minutes; OATA allows up to 30 minutes for grazing species.
• Protein: on alternate days, chopped mussel, prawn or thawed bloodworm instead of part of the pellets.
• Vegetables: a piece of parboiled potato or a vegetable wafer once or twice a week.
• Timing: feed near its cave around lights-out, when this reclusive fish is most likely to come out.

Remove anything uneaten the next morning. Meaty foods foul the water quickly, so feed what is cleared and no more, and watch the belly: rounded is right, hollow means it is not getting its share.

Introduce and handle it safely

Add the fish only to an aquarium with a mature filter, ammonia and nitrite at zero and the temperature already set. OATA recommends the floating-bag method: switch the aquarium lights off, float the sealed bag for about 10 minutes so the temperatures match, then add small amounts of tank water to the bag over up to 20 minutes before releasing the fish with as little bag water as possible. Our guide on how to acclimatise new fish walks through each step.

Handle it with care. Its odontodes and fin spines snag in nets and can puncture bags, which is why OATA advises double-bagging catfish and handling them carefully. Guide it into a container rather than lifting it in a net, and keep your hands clear of its spines.

Use a first-week checkpoint plan

Make it the centrepiece and choose midwater company

Planet Catfish calls L025 aggressively territorial and warns that it may cause problems with similar-sized night-active fish. It notes that big, tough plecos are often kept with large, brutish fish such as oscars, but advises against it for Pseudacanthicus: the combined waste would demand monumental filtration. Its recommendation is to treat the cactus pleco as the centrepiece and stock the tank with medium-sized, preferably omnivorous fish, adding that barbs of all sizes work surprisingly well.

From our barbs, the Denison Barb and the Clown Barb are active, medium-sized midwater fish of that kind. Check each species' own temperature and water range against this pleco's with our tank mates tool before mixing.

Screen companions with suits and avoid

If you are choosing between cactus plecos, compare it with the L114 Leopard Cactus Pleco, the L273 Titanicus Pleco and the related Adonis Pleco. They are alternatives, not tank mates: two spiny giants in one tank will fight over territory.

Watch for health problems early

OATA's warning signs for catfish apply: clamped fins, flicking against gravel or décor, shimmying, changes in breathing or appetite and long spells of hiding. With a large carnivore, poor water from waste and leftover food is the most likely cause of trouble, so test before you treat.

Pair each observation with an action

Do not diagnose from one sign alone; similar behaviour can follow poor water, low oxygen, bullying or hunger. If white spots appear, our white spot treatment guide explains the next steps; read any medicine's label for warnings about catfish before using it. Our pleco care guide covers the routine checks that apply to every suckermouth catfish.

Learn from a recorded aquarium spawning

Planet Catfish's data sheet still describes breeding as unknown but almost certainly in caves, yet it also links to a detailed hobby spawning. In that 2009 account, a keeper bought three mature wild adults and housed them in a 1,600-litre Xingu-style aquarium with other river fish. After a nitrate spike he made three large water changes, mostly with rainwater, and the temperature fell to 24°C. The male was soon seen fanning inside a deep cave with a second fish that later proved to be a female, and a week later the pair spawned in another cave, the male guarding a large clutch by covering it with his body and fins.

When a predatory cichlid began raiding the cave, the keeper removed the eggs to a hastily set-up 54-litre nursery. Many were lost; hatching began six days after spawning rather than the eight days he expected at 28°C. The fry only fed well once the nursery was covered and warmed from about 25–26°C to 28°C, and 32 fry were still alive at 30 days. He concluded that the clutch had been moved too early and that a bare-bottomed nursery with daily water changes stopped the losses.

Note the sexing clues from that keeper

• Males were much slimmer than females, with a longer head.
• His males looked more red, his females more brown.
• The dorsal, tail and pectoral fins were smaller on the females; the females' tail lobes were only 2–3 cm long, far shorter than the males'.
• These clues come from fish of 30–35 cm standard length and may not apply to young fish.

Answer Scarlet Cactus Pleco buying questions

What is a Scarlet Cactus Pleco?

It is L025, Pseudacanthicus pirarara, a large spiny pleco from the lower and middle Rio Xingu and its tributaries the Rio Bacajá and Rio Iriri in Brazil. It has a dark body with black spots, rows of pointed odontodes along its sides and red to scarlet fins. It was known only by its L-number until it was described in 2016.

How big does an L025 pleco grow?

Very big. Planet Catfish gives 450 mm standard length and notes that individuals over 40 cm have been imported; FishBase gives a maximum of 40.5 cm total length and 950 g. Plan for a fish of 40–45 cm.

What size aquarium does it need?

No minimum is published for L025 itself. Seriously Fish asks for at least 180 × 60 cm (about 648 litres) for the smaller 25 cm L114 cactus pleco, OATA says very large fish often need well over 500 litres, and the breeder who spawned L025 kept his adults in 1,600 litres. Treat 180 × 60 cm as the floor and plan larger for an adult.

What does it eat?

Meaty foods. Planet Catfish calls it a carnivore, though not a predator, with prawns and chopped mussel as favourites, plus some vegetable matter to balance the diet. Sinking carnivore pellets and frozen bloodworm make good everyday foods.

Is the Scarlet Cactus Pleco aggressive?

It is aggressively territorial over its cave. Planet Catfish warns that it will fight for territory and, with its spines and hooks, can cause serious damage, especially to similar-sized night-active fish. Keep it as the only large bottom dweller.

What water conditions does it need?

Planet Catfish gives 24–26°C and pH 6.0–7.4 with clear, well-oxygenated water; the published spawning took place near 28°C. Keep ammonia and nitrite at zero and nitrate within 20 mg/l of your tap water.

Is L025 the same as L024?

No. Planet Catfish says L025 is similar to L024 but has considerably more red in the fins, more pronounced black spots and a distinctive hooded, almost "evil" look to the eyes.

Has it been bred in aquariums?

Yes, rarely. Planet Catfish published a 2009 account of a spawning in which the male guarded a large clutch deep inside a cave and 32 fry were raised. It is a cave spawner with male brood care.

Consult the care references

• Planet Catfish: Pseudacanthicus pirarara (L025) — names, L025 code, type locality, etymology, size, identification of the cactus-pleco group, comparison with L024, sexing, distribution, water values, feeding, décor and tank mates.
• Planet Catfish, Shane's World: Spawning Pseudacanthicus sp. L025, the scarlet cactus pleco — a keeper's 2009 account of spawning L025 in a 1,600-litre aquarium, with cave depth, water changes, temperatures, hatching and fry rearing.
• FishBase: Pseudacanthicus pirarara — classification, distribution in the Rio Xingu, maximum total length and weight, and conservation status.
• Chamon & Sousa 2016, Journal of Fish Biology: original description — peer-reviewed original description of Pseudacanthicus pirarara (Chamon & Sousa, Journal of Fish Biology, 2016).
• Seriously Fish: Pseudacanthicus cf. leopardus (L114) — aquarium size, river-style décor, water values, filter and heater sizing, diet and sexing for the related L114 cactus pleco, used where nothing is published for L025.
• OATA: How to look after freshwater catfish — UK guidance for catfish on water quality limits, testing, maintenance, double-bagging, acclimatisation and warning signs.
• OATA: How to look after very large fish (tankbusters) — UK guidance on very large aquarium fish: tank size, filtration, protected heaters, secure décor and a cover.
• Tropical Fish Co delivery policy — current dispatch days and Live Arrival Guarantee terms.