Taxonomy & naming
Hasemania piatan was described by Angela M. Zanata and João Paulo Serra in 2010 as a new species from the upper rio de Contas basin in Bahia, Brazil. The holotype (MZUSP 104538, 2 in SL) was taken from riacho Três Morros and the nearby córrego das Piabas, two small tributaries within that drainage. The valid name as listed in Eschmeyer's Catalog of Fishes is Hasemania piatan Zanata & Serra, 2010.
The genus Hasemania is a small South American characid genus within the broad family Characidae. Members of Hasemania are closely allied to — and were historically confused or synonymised with — Hemigrammus and Moenkhausia, but the genus has been maintained on the basis of consistent morphological characters, most notably the absence of scales on the upper caudal-fin lobe. Hasemania piatan is distinguished from its congeners by 18 principal caudal-fin rays, a meristic character noted in the original description. The specific epithet piatan derives from a local toponym, reflecting the Piata region of Bahia where the type locality is situated.
Morphology
Hasemania piatan is a small tetra reaching approximately 2 in standard length in adults, based on the holotype and associated type series. Like other Hasemania it is a moderately slender, laterally compressed characid with the typical tetra body plan: a small adipose fin behind the dorsal fin, a forked caudal fin, and a terminal mouth bearing fine teeth.
A diagnostic character in the original description is the count of 18 principal caudal-fin rays, which separates H. piatan from related species in the genus. Detailed colouration notes specific to live specimens in the field were not available in sources examined for this article; the species shares the Hasemania pattern of subdued silvery-bronze body coloration seen across the genus, without the bold chromatophore bars of some Hemigrammus relatives. Published data on sexual dimorphism are limited, though as in most small characids females are expected to carry a fuller abdomen when gravid.
Habitat
Hasemania piatan is known from small tributaries of the upper rio de Contas drainage in the state of Bahia, northeastern Brazil — specifically riacho Três Morros and córrego das Piabas near Piata. The rio de Contas is an important Atlantic Forest river system draining eastward to the coast of Bahia. The upper reaches where H. piatan occurs are small, shaded stream channels typical of humid upland Atlantic Forest habitat, characterised by clear to moderately tea-stained water, sandy or rocky substrate, leaf litter banks, and marginal vegetation.
No formal water-chemistry data specific to the type-locality streams of H. piatan were available in sources examined for this article. Streams of this type in the Bahian highlands generally tend toward soft, slightly acidic to neutral conditions, moderated by the regional geology. The species' restriction to this small set of headwater tributaries within a single river system defines both its rarity and its vulnerability: a heavily endemic fish with nowhere else to go.
Feeding
No published dietary study specific to Hasemania piatan was available in sources consulted for this article. As a small characid of Atlantic Forest streams, the species likely feeds opportunistically on the prey available in small tributary environments: aquatic and terrestrial invertebrates — insect larvae, small crustaceans, surface-fallen insects — along with microalgae and organic detritus from leaf litter.
This guild-based inference is consistent with the feeding ecology documented across Hasemania and closely related small Characidae occupying similar Neotropical stream habitats. Until specific stomach-content or stable-isotope studies are published for H. piatan, dietary detail beyond this guild characterisation remains uncertain.
Mating
No published behavioural or reproductive observations specific to Hasemania piatan in either wild or captive settings were available in sources consulted for this article. The genus Hasemania is conventionally regarded as an egg-scattering, open-water or plant-associated spawner without parental care, following the typical small-Characidae reproductive mode.
Congeners and related small tetras of similar body plan typically scatter adhesive or slightly adhesive eggs among fine-leaved submerged vegetation or over sandy substrate, with no guarding or brooding by either parent. Whether H. piatan exhibits any seasonality tied to the Bahian highland rainfall pattern — as is common for stream characids whose reproductive cycles track wet-season flow and food availability — is not documented in the available literature.
Breeding
Hasemania piatan has not been reported in the aquarium trade and is not known to have been bred in captivity. As a wild-endemic, threatened species from a geographically restricted range in northeastern Brazil, it is unlikely to be encountered outside specialist ichthyological collections.
By analogy with other Hasemania species — notably the well-studied Hasemania nana, which breeds readily over fine-leaved plants and spawning mops — H. piatan would be expected to deposit small adhesive eggs that the parents do not attend, hatching in several days at tropical temperatures. However, applying care data from H. nana to H. piatan with confidence is not warranted given the absence of any captive documentation; it is noted here only as a genus-level reference point.
In the aquarium
Hasemania piatan is not known to the aquarium hobby and is not available through normal commercial channels. It is a threatened endemic described only in 2010, and no captive husbandry data are available from the sources consulted for this article. The absence of any Seriously Fish profile, specialist forum reports, or trade records examined for this work confirms that it has not meaningfully entered the ornamental fish trade.
Aquarists interested in keeping Hasemania species can find well-documented information on the closely related Hasemania nana (Silvertip Tetra), which is widely captive-bred, peaceful, and undemanding in a planted aquarium. H. piatan should be considered strictly a wild species of scientific and conservation interest, not a target for collection or trade.
Conservation
Hasemania piatan is assessed as Endangered (EN) on the IUCN Red List. The listing reflects the species' extremely narrow endemic range — a small cluster of headwater tributaries in the upper rio de Contas basin of Bahia — combined with the ongoing threats facing Atlantic Forest stream fish throughout northeastern Brazil. Atlantic Forest rivers in the Bahian highlands are under pressure from agricultural land conversion, riparian forest removal, water extraction, and siltation from pasture and cultivation on poorly buffered upland soils.
H. piatan has been highlighted as a conservation priority by the Brazilian Alliance for Extinction Zero (BAZE), which identifies it among threatened endemic Brazilian fishes requiring targeted intervention. A species restricted to just a handful of small streams within a single sub-drainage has very limited demographic buffer against localised disturbance events. No captive assurance population is known. The most immediately effective conservation actions for H. piatan are protection and restoration of riparian forest cover in the upper rio de Contas headwaters, and prevention of the agricultural runoff and sedimentation that degrade the clear-water stream habitat on which it depends.