Remarks
Best kept as a group in a large aquarium. Territorial when breeding
Care
The Threadfin Acara is known from northern parts of the Amazon basin in Brazil, Colombia, and Peru, including the lower Rio Branco, Rio Capim, Rio Negro, Rio Putumayo, Rio Trombetas, and Rio Xingu, along with the Essequibo River drainage in Guyana. The aquarium should be biologically mature and spacious, with a large expanse of soft sand substrate as these fish like to sift through the substrate in their ongoing search for food items. Provide plenty of hiding places and visual barriers amongst tangles of driftwood, rocky caves, and robust planting cultivated on the wood (such as Anubias sp. or Java Fern). Vegetation planted into the substrate is likely to be dug up, so is best avoided. Filtration should be efficient with areas of moderate water movement and some calmer resting spots out of the current. Frequent partial water changes will help keep nitrate to a minimum, particularly important as this species is sensitive to deteriorating water conditions. Juvenile and sub-adult Threadfin Acaras are usually relatively peaceful. However, the behaviour of adult individuals can be a bit unpredictable, with some showing marked aggression towards conspecifics. It is best to obtain a group of 8 or more juveniles of similar size, and add them to the tank simultaneously so that a natural hierarchy can form. This will not only meet their social needs but it will help spread any minor aggression amongst the shoal, so that no one fish bears the continual brunt of any antagonistic behaviour. If a pair does form naturally from the group, it may be wise to move the remaining fish to another aquarium for their own safety. However, in really spacious quarters, with a plethora of visual barriers, it may be possible to keep multiple pairs. Tankmates should be of similar size and temperament and enjoy the same soft, acidic conditions, avoiding any species which nip fins.
Feeding
Omnivorous. Requires small aquarium foods compared to its adult size. Try to keep it varied with good quality carnivore and herbivore flakes, small sinking pellets, and a mixture of frozen foods such as white mosquito larvae, bloodworm, black mosquito larvae, vitamin-enriched brineshrimp, and daphnia.
Breeding
The Threadfin Acara has a fascinating reproductive method in the wild. The female fish digs a burrow into the substrate (often a compacted mixture of sand and peat) with an almost vertical entry tunnel that gradually levels out horizontally the further it goes. There may be more than one entrance to the central nuptial chamber where the eggs will be deposited, and also some false entrances that lead nowhere. Once the burrow has been excavated, the female actively solicits suitable male fish who swim past. If a male is receptive, the pair set out and defend a territory above the burrow complex some 2-3m in diameter, with the nuptial chamber at the centre. Following an elaborate courtship ritual, up to 2000 eggs are deposited/fertilised in the nuptial chamber, and it is the female who cares for the eggs whilst the male patrols the general perimeter of the territory. Once the fry have become free-swimming, the adults show great parental care and will signal to the youngsters to return to the safety of the burrow should danger approach. This guardianship continues until the fry reach around 12mm in length. Such a complex reproductive method is obviously very difficult to replicate in the home aquarium, and it is further complicated by the extreme intraspecific aggression sometimes observed between breeding pairs. However, there have been a handful of success stories - and spacious quarters, coupled with careful observation (and a means of separating the pair should things become too rough) have proven essential. The most successful substitute spawning burrow has been a large, upturned flowerpot with an entrance hole hewn into the base (which will be the top when the flowerpot is inverted). It would seem that raising the water temperature to the top of the preferred range over the course of a few days, and then lowering it with a large, slightly cooler water change, and repeating this over and over again may trigger a spawning response. The fish must be observed rigorously during this time, as it is not uncommon for one of the pair to maul the other, sometimes with fatal consequences. Always have a tank divider to hand.
