The Uaru, or Triangle Cichlid, is a large peaceful Amazonian cichlid with a plant-based diet, needing soft water and a tank of 300 litres or more.
Overview
Uaru amphiacanthoides is one of the few genuinely large South American cichlids with a peaceful disposition. In the wild it inhabits slow-moving Amazon tributaries — the Rio Negro, Trombetas and Uatumã — and the seasonally flooded forests of Brazil and Guyana. This is classic blackwater: very soft, acidic, darkened by tannins, packed with submerged timber among which the fish stay.
Adults reach 25-30 cm on a tall, strongly laterally compressed body and live 8-10 years. The colouration changes dramatically with age, which regularly surprises buyers: fry and juveniles are mottled brown, matching fallen leaves, and only at eight to twelve months do they take on adult dress — a beige-ochre body with a large black triangular blotch on the flank, a black "apron" across the throat and a ruby-red iris. That blotch is what gives the species its common name.
Sexing by appearance is essentially impossible: males are usually slightly larger and heavier-bodied, but there are no reliable markers — pairs form on their own out of a group of juveniles.
In temperament the Uaru is closer to the Discus than to a typical cichlid: a calm, social fish that stays in a group, yet is skittish and highly sensitive to water quality. A sudden movement near the tank sends it dashing, so a busy walkway is the wrong place for the aquarium. Care level is intermediate, and that is dictated not by temperament but by the demands on water and volume.
Tank Requirements
The minimum for a pair is 300 litres, but a group of five or six — which is how the species looks best — needs 500-600 litres and a tank at least 150 cm long. Uaru are tall fish, so height matters too: no less than 50-60 cm.
Water parameters: temperature 24-28 °C, pH 5.5-7.0, general hardness (GH) 2-8 dGH. This is fundamentally a soft-water species, and the upper end of that range is best left unused: the optimum is pH 6.0-6.8 and GH 2-5. In hard alkaline water the fish survives, but it fades, falls ill more often and will almost certainly never spawn.
Use fine sand as substrate, since Uaru sift it for food. Build the layout around large pieces of driftwood and branches recreating the flooded forest, plus a few open areas and flat stones. Dried almond or oak leaves acidify the water and double as food — the fish graze on the softened leaf litter.
With live plants you will have to accept losses: Uaru are pronounced herbivores and will strip any soft-leaved greenery. Only tough-leaved anubias, microsorum and java fern attached to the hardscape genuinely survive; everything else is best regarded as consumable food.
Filtration must be powerful but the flow moderate — an external filter with a spray bar directed along the glass. A lid is mandatory, as a startled fish will jump.
Feeding and Diet
Uaru amphiacanthoides is a rarity among large cichlids: a primarily herbivorous species. In nature its diet is built on aquatic vegetation, softened leaf litter, detritus, and seeds and fruit from the flooded forest, with small invertebrates as no more than a supplement. Reproduce this, or health problems are unavoidable.
The staple should be quality vegetable foods: spirulina flakes and pellets, algae wafers for herbivorous catfish, and blanched courgette, spinach, lettuce leaves, cucumber and green beans. Vegetables can be clipped to a suction holder or weighted down with a stone — the fish will graze on them through the day.
Give the protein portion in measured amounts, once or twice a week: bloodworms, brine shrimp, mysis, daphnia. Excess animal food is the most common mistake in keeping Uaru and a direct route to hexamitiasis and fatty organ degeneration. Beef heart and other warm-blooded meats are excluded entirely.
Feed adults once or twice a day, juveniles three times. Remove uneaten vegetables after a few hours, or they will foul the water quickly.
Care and Maintenance
Uaru are exacting about water cleanliness — on this count they rival Discus. A weekly 25-30% change is mandatory, and at heavier stocking two 20% changes a week make more sense. Prepare the water in advance: if your tap water is hard, blend it with RO water down to GH 2-5.
Keep nitrate below 20 mg/l, with ammonia and nitrite at zero. Vacuum the open areas of sand weekly: this is a large fish and it produces a lot of waste. Rinse filter media in old tank water every three to four weeks.
The species' signature illness is hexamitiasis, also called hole-in-the-head or head and lateral line erosion: pits on the head and along the lateral pores. It almost always arises from two causes — excess protein in the diet and accumulating nitrate. It responds to metronidazole, but not letting it start is far easier: a plant-based diet and consistent water changes essentially close the question. The second common scenario is ich following a chill during a water change.
Watch behaviour daily. A healthy Uaru swims calmly in the middle layer, feeds keenly and shows a crisp black blotch. Overall darkening of the body, hanging in a corner, refusing food and whitish stringy faeces are signals that call for an immediate water test.
Compatibility
Despite its size, U. amphiacanthoides is a peaceful fish with no claim on anyone else's territory outside of spawning. The rule for choosing tank mates is simple: comparable size, calm temperament, and the same soft warm water.
The best companions are South American species from a similar biotope: Discus, Angelfish, Severum Cichlid, Flag Cichlid, Demon Eartheater and Acarichthys heckelii. The middle layer is nicely animated by larger shoaling characins — Red-Eye Tetra, Penguin Tetra. On the bottom, Sterba's Cory and the Royal Pleco fit well, the latter also processing the driftwood.
Unsuitable: small fish (neons, rasboras, guppies) — the Uaru will eat them, with no aggression involved; large aggressive cichlids such as the Oscar, which will quickly overwhelm a timid Uaru; ill-tempered herbivorous competitors like the Banded Leporinus, which nips fins; and any species requiring hard alkaline water.
While spawning, a pair claims a corner of the tank and drives off anything that approaches — though without injuries, limiting itself to display. Keep the species in a group of five or six: a lone fish grows dull and even more skittish.
Breeding
Breeding U. amphiacanthoides is an advanced undertaking, and the main barrier is the same as with Discus: water chemistry. Above 4-5 dGH the eggs mostly fail to fertilise or go white within the first day.
Do not hand-pick a pair — take six to eight juveniles, grow them on together and wait for the fish to sort themselves out. Sexual maturity comes at one and a half to two years, at around 15 cm. An established pair is easy to spot: the two fish stay together, clean their chosen surface as a team and keep the others away.
Spawning conditions: temperature 27-29 °C, pH 5.5-6.5, GH 1-4 dGH (in practice almost always remineralised RO water), dim lighting and complete freedom from disturbance. As a substrate the pair chooses a vertical or sloping surface — a thick piece of driftwood, a flat stone, a ceramic pipe. A clutch runs to 200-400 eggs.
Parental care is fully biparental: both fish fan the eggs, remove those that go white and, after hatching, move the larvae into a pit they have dug. Incubation takes about three days, and the larvae spend another four or five finishing their yolk sacs.
Then comes the remarkable part: like Discus, Uaru fry feed for their first one to two weeks on the parents' skin secretions, literally covering their flanks. The adults must not be removed at this stage — without that "milk" the brood mostly dies. From around day 10-14 the fry can be supplemented with brine shrimp nauplii and microworms, with vegetable foods introduced gradually. The young are very sensitive to nitrate, so a grow-out tank needs daily 10-15% water changes. Adult colouration appears only at eight to twelve months.