Taxonomy & naming
Harttia guianensis was described by Lúcia Rapp Py-Daniel and Cláudio de Oliveira in 2001, in Ichthyological Exploration of Freshwaters (volume 12, number 1, page 88, figure 6). The Catalog of Fishes (Eschmeyer, CAS) gives the authority as Rapp Py-Daniel & Oliveira, 2001, matching the publication date of the volume in which the species appeared. (A secondary aquarium-hobby data field has at times shown '2011' for the year, but this is a transcription error against the 2001 volume; the 2001 date is the one used here, following the Catalog of Fishes.) The species has no synonyms — it was named directly into Harttia and has remained there.
The type locality is the Approuague River at Saut Athanase (approximately 4°11′N, 52°19′W), French Guiana. Within the family Loricariidae the species belongs to the subfamily Loricariinae, the depressed-bodied whiptail catfishes distinguished by a long, slender caudal peduncle and a ventral suckermouth flanked by barbels.
Morphology
Harttia guianensis reaches about 6.9 inches standard length, a moderate size for the genus. Like other Loricariinae it has a strongly flattened body, an elongate posterior trunk tapering to a thread-like caudal peduncle, and the protective covering of bony scutes shared across the armoured catfishes. The mouth is ventral, forming a sucker disc adapted both for grazing and for holding station against flow.
The original 2001 description provides the diagnostic meristic and morphometric detail that separates H. guianensis from its congeners, but beyond that account the accessible literature offers little additional description of live coloration. No species-specific data on sexual dimorphism has been published, though hypertrophied head and pectoral odontodes in breeding males are common across the genus.
Habitat
The species occupies coastal rivers of the Guianas. FishBase and the Cat-eLog record it from the Approuague and Sinnamary basins of French Guiana, extending westward into the Marowijne (Maroni) drainage on the French Guiana–Suriname border. The type locality at Saut Athanase is a falls/rapids site on the Approuague, indicating a preference for flowing, well-oxygenated reaches over rock and gravel.
These Guiana Shield rivers are typically clear to lightly stained, warm, soft, and slightly acidic to neutral. No specific physico-chemical field measurements for H. guianensis are published in the accessible sources, so precise temperature and pH values for its habitat should be regarded as undocumented. Its flattened build and suckermouth are consistent with the rheophilic, substrate-clinging lifestyle typical of the genus.
Feeding
No dedicated dietary study of Harttia guianensis has been published. As a ventral-mouthed loricariine of flowing waters, it is presumed to graze aufwuchs — the algal and biofilm film, with its associated micro-invertebrates — that develops on submerged rock and gravel, supplemented by fine detritus. This is the standard feeding ecology for the genus and is consistent with the species' morphology, but it is inference rather than recorded observation for H. guianensis specifically.
Mating
Mating behaviour for Harttia guianensis has not been documented in the accessible literature. Several Harttia species are substrate spawners in which the male tends the eggs, and breeding males often develop enlarged odontodes on the snout and pectoral rays, but whether H. guianensis conforms to this pattern has not been confirmed by published observation. No data published.
Breeding
No breeding account for Harttia guianensis exists in the accessible sources, from the wild or in captivity. By analogy with congeners, substrate egg-laying with male guarding of an adhesive clutch would be the expected mode, but this is extrapolation from related species rather than recorded fact for this fish. The species is rare in the aquarium hobby and its reproduction remains undocumented.
In the aquarium
Harttia guianensis is rarely encountered in the aquarium trade and carries no L-number. As a rapids-associated whiptail of moderate size, it would require a tank with brisk, well-oxygenated flow, a substrate of smooth rock and gravel, and consistently clean water with ammonia and nitrite held at zero. Soft, slightly acidic to neutral water at tropical temperatures suits its Guiana Shield origins, though exact maintenance parameters are not documented for the species.
Its diet in captivity would centre on algae- and biofilm-based grazing, in keeping with its presumed wild feeding. This is a fish best regarded as a subject for the specialist keeper able to provide flowing-water conditions rather than a general community aquarium.
Conservation
The IUCN Red List lists Harttia guianensis as Least Concern. The species occurs across several coastal river basins of the Guiana Shield — the Approuague and Sinnamary in French Guiana and the Marowijne toward Suriname — and no major range-wide threats have been identified. As with other rapids specialists of the region, the principal long-term concerns would be habitat alteration from hydroelectric development or sedimentation from mining, but none is currently flagged as a significant threat to this fish.