One of the most robust and active tetras available to aquarists is a mid-sized fish hailing from the subtropical waters of South America, the Buenos Aires Tetra. This charismatic characin sports some gorgeous red fins and a prominent black marking just before the tail, all set against a bright, silvery body.
Rather than the warm temperatures that bathe the Amazonian river basin in the north, the Paraná river system that this fish calls home tends towards cooler temperatures that can range anywhere from 60–80ft, meaning that this fish is quite fine in a broad range of aquariums, whether it’s a traditional tropical community setup, a room temperature environment, or, in warmer climates, an outdoor pond.
Like most tetras, this fish benefits from being kept in large groups, preferably a half-dozen or more. Over the years, H. anisitsi has acquired a reputation as a fin-nipper, but this poor behavior is largely the result of being kept in numbers that are too few or in tanks that are too small. A lone little Buenos Aires Tetra in a small tank is probably going to cause some trouble if it's kept with more tranquil species with long, dangling fins. But, in a large system with plenty of friends to play with, there is little issue mixing this fish with others.
Males can be told from the similar females on account of their brighter colors and smaller, more streamlined bodies. Neither sex gets much over three inches, making this an ideal fish for tanks measuring around 30 gallons or more. Spawning is a regular occurrence when these fish are well cared for, resulting in many eggs scattered about the bottom. Usually, these won’t result in any surviving fry, but, in a densely planted aquarium, it’s not unheard of for some young to make it into adulthood.
As an omnivore, a mixed diet of flake, pellet and frozen food will keep your tetras in top shape, and any foods loaded with carotene or astaxanthin will likely help them to reach their brightest colors. They also naturally feed to some extent on detritus and plant matter and, if kept with delicate plants, have been known to cause a bit of damage to foliage.
There are quite a few species from South America that would make for good regional tank mates, including callichthyiid catfishes (Corydoras, Callichthys) other active characins (Leporinus, Chalceus and some of the other larger tetras), and any of the armored loricariid catfishes and peaceful cichlids (Geophagus, Satanoperca), just to name a few. Many other fishes from outside this region work equally well, such as rainbowfishes, larger barbs, etc. Just be sure to avoid anything overly lethargic or long-finned, such as many anabantoids (gouramis, bettas) and Pterophyllum angelfishes.
One last note, a newly described and closely related species, H. togoi, was reported from the waters near Buenos Aires, indicating that H. caudovittatus, the Buenos Aires Tetra, is not actually from Buenos Aires! It’s probably never even been to Carnival!