Red-tailed Catfish

Phractocephalus hemioliopterus is a giant long-whiskered catfish of the Amazon and Orinoco basins, inhabiting everything from rapids to flooded forest across much of northern South America. FishBase records a maximum of 135 cm TL and 44.2 kg, making it one of the largest catfishes ever offered in the aquarium trade. It is sold cheaply as a 5 cm juvenile, and Seriously Fish documents the consequences: public aquaria saturated with donated adults and feral populations established by dumped fish in the USA and several other countries. Both FishBase and specialist references treat it as an expert or public-aquarium species rather than a home-tank fish.

Expect a typical captive adult of roughly 100-130 cm (3-4 ft) and tens of kilograms; FishBase's maximum is 135 cm TL, while its common wild length is only 60 cm TL, so hobby fish grown in good space approach the top of the range. Growth is explosive during the first years - Aquarist Atlas reports roughly 1-2 inches (2.5-5 cm) per month - and sexual maturity does not arrive until about 85 cm TL, at which point the fish already exceeds virtually all home aquariums. The largest recorded specimen measured 134 cm and weighed over 40 kg. With proper housing the species lives 15-20 years or more.

Redtails are nocturnal, gape-limited predators: Aquarist Atlas describes a 'nocturnal predator that requires large cave-like cover' that hunts mainly at night using its barbels. They are solitary and territorial with their own kind - Seriously Fish reports territoriality toward conspecifics and other large pimelodids, and ScotCat calls the fish 'definitely a loner' that will quickly kill tank mates. In cramped quarters they become stressed bulldozers, smashing heaters and shoving decor around. Despite their predatory nature they are famously personable, often begging for food like dogs, but friendliness never overrides the size of their mouth.

For a single adult, Seriously Fish gives an absolute minimum of 360 x 240 x 120 cm (about 10,368 litres), and Aquarist Atlas independently repeats the same 360 x 240 in footprint. Filtration must be sump- or pond-scale because a 44 kg carnivore produces what Aquarist Atlas calls a 'commensurate bioload'. Keep the lighting dim with only large, anchored pieces of bogwood or smooth rock - or no decor at all - and use bare bottom or fine sand, since gravel can be swallowed or jam in the gills. ScotCat notes that height matters little (18-24 in is ample) but the tank must be at least 8 ft long with roughly 36 in of width so the fish can turn.

Volume is the wrong metric here: what the fish needs is floor. A 1.2-1.3 m predator must be able to turn and cruise, which is why Seriously Fish specifies a 360 x 240 cm base even for its 'absolute minimum', and ScotCat still insists on an 8 ft tank about 36 in wide 'so that it can turn comfortly'. Pet Zone Tropical Fish reduces the principle to 'Length > Depth > Height: They need floor space more than vertical space'. A 500-litre tank of any height fails this test because its length is typically under 150 cm.

Diet is carnivorous and opportunistic: FishBase records adults feeding on 'fish, crabs and fruits', and Seriously Fish lists wild fish, invertebrates and fallen fruit. Offer varied meaty foods - prawns, mussels, earthworms, whitefish fillets and large sinking carnivore pellets - and avoid mammal meat and feeder fish, which Seriously Fish warns risk organ damage and disease introduction. Adults need at most 'a single meal per week' (Seriously Fish) or two to three sizeable meals (Aquarist Atlas), never daily portions. Overfeeding is a leading cause of death, and redtails swallow inedible objects, so keep small gravel and trinkets out of the tank.

Compatibility turns entirely on mouth size: Aquarist Atlas states it 'will consume any tankmate it can engulf', so anything shorter than about half the catfish's length is food. At public-aquarium scale suitable companions exist - Seriously Fish suggests doradids such as Oxydoras niger or Pterodoras granulosus, plus very large characins and cyprinids in deep water. For ordinary keepers the honest answer is a single fish: ScotCat warns it 'would quickly kill any tank mates', and Seriously Fish says it should be the only large pimelodid present unless space is truly unlimited. Snails, shrimp and crabs should also be assumed edible.

Blunt verdict: no for a private aquarist - only an exceptional keeper with an indoor pond or a custom 3-4 m tank should attempt this fish. Seriously Fish itself states 'we do not recommend keeping this species in the home', and Aquarist Atlas concludes it 'belongs in a public aquarium or specialist facility, not a home tank'. Buying the cheap 5 cm juvenile is a documented size trap that ends in stunting, surrender or illegal release. If you cannot guarantee adult-sized housing for 15-20 years starting today, do not buy it.