Taxonomy & naming
Myleus altipinnis was described by the French ichthyologist Achille Valenciennes in 1850. It belongs to the family Serrasalmidae — piranhas, pacus and silver dollars — within the order Characiformes, and to the genus Myleus, one of several silver-dollar lineages in that family. Serrasalmidae taxonomy has been heavily revised since the mid-twentieth century, with a number of species once placed in a broadly defined Myleus later split out into Myloplus, Tometes and Ossubtus as the Catalog of Fishes (Eschmeyer, California Academy of Sciences) refined generic boundaries; M. altipinnis has remained in Myleus.
The species epithet altipinnis is straightforward Latin for "high-finned," a reference to the tall dorsal fin typical of the genus. As with other Myleus and silver-dollar species in the trade, exact identification can be difficult for hobbyists, since several genera share the same disc-shaped, silvery body plan and juveniles in particular are easily confused between species.
Morphology
Myleus altipinnis has the classic silver-dollar profile: a strongly laterally compressed, disc-shaped body, a tall dorsal fin (reflected in the species name), and a bright, mirror-silver flank typical of open-water serrasalmids. FishBase records a maximum size of 13 in standard length for the species, making it one of the larger silver dollars kept in the hobby — reports of aquarium specimens commonly cite sizes around 10 in, still a substantial fish for a community tank.
The jaw carries the family's signature dentition — a single row of interlocking, sharp-edged teeth — but in Myleus this apparatus is adapted for cracking hard seeds and nuts and shearing plant material rather than for taking flesh. Data on colour variation, fin markings and any distinction between juvenile and adult patterning specific to this species is sparse in the sources available; general silver-dollar colouration (bright silvery flanks, sometimes with faint dusky fin edging) is the safest description without over-specifying.
Habitat
Myleus altipinnis is native to the São Francisco River basin in Brazil, a large, isolated South American drainage that does not connect to the Amazon system and hosts a number of endemic fish species. FishBase describes it as a tropical freshwater, benthopelagic species, and hobby sources associate Myleus generally with fast-flowing rivers and rapids, consistent with a build suited to strong current and open water rather than sluggish backwaters.
Specific water-chemistry data (temperature range, pH, hardness) for wild São Francisco populations of this species is not available in the sources consulted here; rather than guess, this account notes only that the São Francisco basin runs warm, tropical freshwater typical of Brazilian river systems, and defers to the cautious aquarium parameters given in "In the aquarium."
Feeding
Myleus altipinnis is herbivorous with some consumption of animal matter, and FishBase specifically describes it as primarily a seed-cracker, adapted in the wild to feeding on nuts and fruit that fall into the river from overhanging vegetation — a foraging strategy shared with several other Serrasalmidae in fast-flowing, forest-margin rivers. Its large mouth and robust dentition are built for exactly this task.
In the aquarium this translates to a need for a genuinely vegetable-forward diet: blanched vegetables, spirulina-based foods and algae wafers should form the bulk of the diet, supplemented with some protein. Keepers should not expect this species to behave like a predatory characin at feeding time — it grazes and crushes rather than hunts — but they should expect it to treat live aquarium plants as food, which is the species' single most consequential dietary habit for tank planning.
Mating
No species-specific courtship behaviour for Myleus altipinnis is documented in the sources available. Hobby accounts of Myleus generally describe them as open-water schoolers whose spawning, where observed at all in captivity, follows the broader silver-dollar pattern of loose pairing within a conditioned group rather than fixed pair-bonding. External sexual dimorphism is not documented for this species in the available sources; this account does not assert a sexing method that has not been verified.
Breeding
Silver dollars in the genus Myleus are egg-scatterers, releasing eggs over fine-leaved plants or plant-like cover in open water, with no nest built and no parental care of eggs or fry. Myleus altipinnis is only occasionally bred in the hobby, and successful spawns are generally reported in soft, acidic water that encourages breeding condition; the eggs and resulting fry receive no guarding from the parents and are vulnerable to being eaten by tankmates, including the parents themselves, if not separated.
Because detailed breeding accounts specific to M. altipinnis are sparse, keepers attempting to spawn this species should look to the wider Myleus and silver-dollar literature for method (soft, acidic water, fine-leaved or artificial spawning mops, removal of adults after spawning) rather than assume any species-specific protocol has been established.
In the aquarium
Myleus altipinnis is a large, active schooling fish — hobby sources put practical aquarium size around 10 in, and a group needs serious swimming room, commonly cited as a minimum of five to six individuals to settle the fish and reduce stress-driven aggression within the shoal. A large aquarium (100+ gallons/380+ litres, more as the group matures) with open water for swimming and strong filtration to handle the bioload is the baseline, not an upper bound.
The single most important care note for this species is that it is a committed plant-shredder: robust, vegetable-hungry silver dollars like Myleus altipinnis will strip a planted tank down to bare stems in short order, and only genuinely tough plants such as Java fern or Anubias have any real chance of surviving alongside them. This is a fish for a hard-scaped tank built around driftwood and rockwork, not a planted aquascape. It is generally peaceful and community-safe with tankmates too large to be seen as food, but its size and swimming energy mean tankmates need to match its scale and activity level.
Conservation
The IUCN Red List assesses Myleus altipinnis as Data Deficient, reflecting limited population data across its São Francisco basin range rather than any documented decline. FishBase notes the species has high resilience and low-to-moderate vulnerability to fishing pressure, which is a reassuring signal even in the absence of a full population assessment.
As a São Francisco basin endemic, M. altipinnis shares the conservation profile of other fish restricted to that drainage — a river system subject to damming, water abstraction and habitat modification pressures common to Brazilian river basins — though no specific threat has been documented for this species in the sources available. Given the Data Deficient status, this account does not assert a conservation trend that is not supported by an assessment.