Taxonomy & naming
Triportheus signatus was described by the American ichthyologist Samuel Garman in 1890. It belongs to the genus Triportheus, a group of laterally compressed, keel-bellied characins often called hatchet-tetras for their superficial resemblance to the true hatchetfishes (family Gasteropelecidae), though the resemblance is convergent rather than close kinship — Triportheus is classified in its own family-level lineage (treated by some authorities as Triportheidae, by others as a subfamily within Characidae) within the order Characiformes, alongside the piranhas, pacus, silver dollars and their many relatives.
FishBase places Triportheus signatus specifically in the Parnaíba River basin and adjacent northeastern coastal drainages of Brazil — a comparatively narrow, well-defined range compared with the wide-ranging Amazonian and Orinocan Triportheus species such as T. angulatus. As with much of this genus, species-level identification within Triportheus can be difficult in the field, resting on details of scale counts, fin-ray counts and keel shape; the cache consulted for this article did not turn up a dedicated original description or revision beyond the FishBase summary, so taxonomic detail here is deliberately kept to what that record documents.
Morphology
Triportheus signatus reaches a documented maximum of 7.5 in total length, per FishBase. Like other Triportheus, it should show the genus's characteristic build: a laterally compressed body, a pronounced ventral keel running from the throat toward the anal fin, and enlarged pectoral fins used to help the fish skitter and leap at the surface — a feature shared with the true hatchetfishes but arrived at independently. A trophic level of roughly 2.8 recorded on FishBase points to an omnivorous rather than strictly predatory diet, consistent with the feeding ecology described in the genus generally.
Beyond these documented points, the cache available for this species does not include a detailed colouration or fin-count description specific to T. signatus, and none is asserted here rather than borrowed from a different Triportheus species.
Habitat
The species is native to the Parnaíba River basin and northeastern coastal river drainages of Brazil, a freshwater benthopelagic environment per FishBase — meaning it occupies the water column rather than living tight to the bottom, consistent with a surface-oriented, actively swimming characin. The Parnaíba is one of Brazil's major independent river systems, running from the interior highlands to the Atlantic coast outside the Amazon or São Francisco drainages, which places T. signatus in a distinct, comparatively less-studied ichthyofaunal province.
Detailed water-chemistry data specific to this species were not found in the cache. Broadly, Triportheus species across South America inhabit warm, lowland tropical rivers and their floodplains; without a specific reading for T. signatus, this article does not assign numeric temperature or pH figures beyond noting the general warm-freshwater context FishBase records.
Feeding
The trophic level of about 2.8 recorded for Triportheus signatus on FishBase is consistent with an omnivorous diet, and the genus as a whole is documented as surface-feeding: Triportheus species patrol the water's surface for fallen insects, fruit, nuts and seeds from overhanging vegetation, supplementing this with other small food items taken near the surface film. There is no indication in the available sources that T. signatus departs from this general pattern.
In the aquarium, closely related Triportheus such as T. angulatus are kept on a varied omnivorous diet offered at or near the surface — small live and frozen foods alongside plant-based flake or pellet — and the same general approach would be the reasonable starting point for T. signatus, understood as an inference from the genus rather than a species-specific finding.
Mating
No courtship or pairing behaviour specific to Triportheus signatus was found in the cache. Data are sparse enough that no useful account of spawning behaviour, sexual dimorphism or pair formation can be given for this species without extrapolating from other characins, which this article avoids doing.
Breeding
There is no documented aquarium breeding record for Triportheus signatus in the sources consulted. For the closely related and better-studied T. angulatus, Seriously Fish states plainly that breeding has not been achieved in aquaria, and the genus generally is not known to be bred by hobbyists. Given the near-identical husbandry profile and the total absence of any breeding account for T. signatus specifically, the honest statement is that this species should be treated as essentially unbred in captivity, not assigned an egg-scattering or any other breeding mode by inference.
In the aquarium
Direct aquarium-care information for Triportheus signatus itself was not found; the best available guidance comes from the closely related and better-documented T. angulatus, which shares the genus's build and behaviour. On that basis, Triportheus species need a large-footprint aquarium with plenty of open surface area, since they are active surface swimmers and strong jumpers — a tightly fitted, gap-free cover is essential, not optional. They are shoaling fish that should be kept in a proper group rather than singly or in pairs, and they do well alongside similarly sized, robust South American tankmates such as Geophagus and Satanoperca cichlids, other mid-to-large characins and catfish that will not see them as food or be seen as a target themselves.
Given T. signatus's modest documented size of under 8 in, a large well-covered aquarium sized for an active shoaling characin is appropriate, but a keeper should treat any more specific stocking or water-parameter number for this exact species as an educated inference from its relatives rather than a confirmed fact, and should expect this to remain a fish for the experienced keeper willing to work from incomplete information.
Conservation
The IUCN Red List assesses Triportheus signatus as Least Concern, and FishBase corroborates this status as of a November 2018 review. This reflects a fish that, while restricted to a specific river system (the Parnaíba basin and adjoining northeastern Brazilian coastal drainages) rather than a continent-spanning range, does not currently face documented threats sufficient to elevate its risk category.
As with many regionally endemic Neotropical characins outside the heavily studied Amazon and Orinoco systems, the Parnaíba basin's fish fauna is comparatively understudied, and ongoing pressures common to Brazilian freshwater systems — damming, water abstraction and land-use change in the watershed — are the kind of long-term factors worth watching even for a species not currently considered at risk.