Buenos Aires tetra

Water parameters

Tolerated range for this species. Aim for the middle of each band rather than the extremes.

Tank and habitat

Substrate: any.

Behavior

Plant interaction: destroys most plants.

Feeding

Omnivorous, fast, and not at all picky. Flake, pellets, frozen bloodworm, frozen brine shrimp, daphnia, blanched vegetables, algae, and live food are all accepted. The natural diet runs to worms, crustaceans, insects, and a meaningful amount of plant material; the species really does eat aquatic plants given the chance. Including vegetable matter (spirulina flake, blanched spinach or zucchini) in regular feeding reduces but does not eliminate the plant-chewing habit, since the behaviour is partly grazing instinct rather than just hunger. Feed twice daily in moderate amounts; growth is fast and the fish always seem ready to eat.

Compatibility

• A larger, more assertive tetra than the typical community species. Around 7 to 10 cm aquarium-grown and noticeably more boisterous than neon-sized fish. Occasional fin-nipper, especially in small groups
• Groups of eight or more keep nipping inside the school and away from tankmates. Smaller groups are noticeably worse
• Not for planted tanks. Soft-leaved aquatic plants get eaten; tough species like Java fern and Anubias are usually left alone. Floating plants are sometimes safer than rooted ones
• Good companions are robust tankmates of similar size or larger: barbs, rainbowfish, larger tetras, peaceful cichlids, and corydoras. Long-finned fish (angelfish, bettas, fancy guppies) and very small nano species are bad pairings
• Cold tolerance down to roughly 14 C makes the species suitable for unheated rooms and for subtropical communities alongside white clouds, rosy barbs, and peppered corys

Origin and habitat

A robust mid-sized characin from southern South America, native to the Parana and Uruguay River basins across Argentina, Paraguay, Uruguay, and southeastern Brazil, with additional populations recorded from coastal Uruguay drainages and watercourses south of the Rio de la Plata estuary. Wild habitat is subtropical: smaller streams, tributaries, floodplain backwaters, and oxbows rather than main river channels, and the species is comfortable in slow water and standing ponds. Despite the common name the fish is not endemic to Buenos Aires. Eigenmann described the species in 1907 as Hemigrammus anisitsi from a Villarica specimen on the Rio Tebicuary in Paraguay's Guaira Department; the genus name shifted through Hyphessobrycon and is sometimes still labelled Hemigrammus caudovittatus in older literature. Following the 2020 phylogenetic revision by Teran, Benitez, and Mirande ('Opening the Trojan house: phylogeny of Astyanax, two genera and resurrection of Psalidodon'), the species was moved to the resurrected genus Psalidodon and now sits in the subfamily Acestrorhamphinae of the American-characin family Acestrorhamphidae. The genus name combines Greek psalis 'scissors' with odous 'teeth' after the dentition. The species epithet honours Juan Daniel Anisits (1856-1911), born in Hungary, later a Paraguayan citizen who worked at the National University of Paraguay and supplied Eigenmann with the specimens used in the description. The same naturalist is the eponym for the bloodfin tetra (Aphyocharax anisitsi) and several other species. The Buenos Aires tetra was first imported to Europe in 1922 from the inflow of the La Plata River and has not left the trade since; almost all stock today is captive-bred. The body is silvery with iridescent flecks, two black humeral spots that intensify with age, a dark caudal-peduncle spot extending through the tail base, an orange to red anal fin tipped with white on the first rays, and an entirely red caudal fin. An albino strain is also available. Records show a maximum length of 13.2 cm TL; aquarium specimens more typically reach 7 to 10 cm. The species is subtropical and tolerates water down to about 14 C, which makes it one of the few tropical-trade tetras suited to unheated or cool tanks. IUCN Least Concern. Records note it is 'one of the hardiest tropical fishes for the home aquarium' and explicitly flags it as a plant-eater.

Breeding

Easy to spawn. Tolerates a wide range of water conditions, including moderately hard water that would stop most Amazon-basin tetras from breeding. Condition a chosen pair on frozen food and live food for a week, then move them into a breeding tank fitted with fine-leaved plants or spawning mops over a bare or mesh base. Spawning starts at dawn and continues for two to four hours, with the female releasing semi-adhesive eggs that scatter through the plants. The species is unusually fertile for its size: a Polish peer-reviewed study (Kujawa 2000) recorded clutches of over 2000 eggs in a single extended spawn, well beyond what most tetras of comparable size produce. The adults eat the eggs once spawning ends, so they need to come out promptly. Eggs hatch in roughly 20 to 24 hours at typical aquarium temperatures. Fry consume the yolk sac for three to four days and then become free-swimming, and take baby brine shrimp almost immediately afterwards. Growth is fast, sexual maturity is reached in a few months, and the species is genuinely a good first egg-laying fish to breed at home.

Common problems

Plant destruction is the defining care issue. The species is among the most enthusiastic plant-eaters in the tetra family; a school of ten will work through the soft leaves of a moderately planted tank within a week or two. The only common plants reliably ignored are tough-leaved species like Java fern, Anubias, and Bolbitis. Keeping Buenos Aires tetras realistically means accepting either a hardscape tank, a tank planted exclusively with tough species, or near-constant replanting. Health problems are rare; the species is genuinely hardy and tolerates parameter swings, cool water (down to about 14 C), and inexperienced keepers. Fin-nipping in small groups is the other behavioural issue; eight or more tetras keep the activity inside the school and out of other species' fins. Jumpers in some setups; a lid is sensible.

Bioload

Further reading

• How to cycle a fish tank
• Stocking ideas by tank size