Taxonomy & naming
Harttia depressa was described by Rapp Py-Daniel and Oliveira in 2001, in a paper presenting seven new species of Harttia from the Amazonian–Guiana region (Ichthyological Exploration of Freshwaters, volume 12, number 1, pages 79–96). The Catalog of Fishes (Eschmeyer, CAS) recognises it as a valid species of Harttia (species id 66298).
The genus Harttia is placed in the subfamily Loricariinae, the elongate, flat-bodied 'whiptail' suckermouth catfishes that lack an adipose fin and carry a long, slender caudal peduncle. The specific epithet depressa is Latin for 'flattened' or 'pressed down', referring directly to the species' conspicuously depressed head and body.
Morphology
Harttia depressa reaches about 5 in standard length. Its defining feature is the strong dorsoventral flattening of both head and body — the head depth fits roughly 2.8–3.2 times into the head length, and the body depth about 3.0–3.7 times into the head length, giving the fish an exceptionally low profile.
In colour, the head and predorsal region are marbled in dark and light brown, while the remainder of the dorsal surface is yellowish with three to four faint transverse brown bars behind the dorsal fin. The dorsal fin is faintly spotted and bears a black blotch at the tips of the first rays. The ventral surface is brown on the snout and upper lip but otherwise unpigmented, and the belly is entirely naked (unplated) from the throat back to the pelvic fins.
Mature males develop a broad, flattened pectoral spine covered over about two-thirds of its length by enlarged odontodes, a reduced rictal barbel, and a large, boomerang-shaped subpreopercular bone — features that distinguish breeding males within the genus.
Habitat
Harttia depressa is known only from the Uatumã River basin in Brazil, a Guiana Shield tributary of the Amazon. As a member of the Loricariinae and given its strongly depressed body, it is adapted to clinging to the substrate in flowing water. Detailed micro-habitat measurements (temperature, pH, flow) for this species are not given in the sources available here, but its body form points to a rheophilic existence on rock and sand in well-oxygenated current.
Feeding
No dedicated feeding study has been published for Harttia depressa in the sources available here. FishBase lists an estimated trophic level of about 2.5, indicating a low-trophic, largely herbivorous-to-detritivorous diet typical of the genus. Like other Loricariinae it most likely grazes biofilm, algae and fine organic material from hard surfaces, but no direct dietary observations are documented.
Mating
No account of courtship or mating behaviour exists for Harttia depressa in the sources reviewed. The pronounced male features — enlarged pectoral-spine odontodes and a modified subpreopercle — are consistent with the male-male competition and substrate-guarding reproductive strategy seen across Loricariinae, but no species-specific mating observations have been published.
Breeding
No breeding has been documented for Harttia depressa, in the wild or in captivity, in the sources available here. The species is not present in the aquarium hobby in any meaningful way, and no reproduction reports are known. While many Harttia are substrate spawners with paternal egg care, no data has been published for this species specifically.
In the aquarium
Harttia depressa is effectively absent from the aquarium trade, and no husbandry information exists for it. Any care guidance would be extrapolated from other rheophilic Harttia — strong flow, high oxygenation, clean clear water, and a substrate of sand and smooth rock at tropical temperatures. Given its restricted and threatened wild status, this is a species best left in the wild; no genuine captive-keeping data is available.
Conservation
The IUCN Red List assesses Harttia depressa as Endangered, under criteria B1ab(i,iii,iv) (assessment dated 7 November 2018). The listing reflects the species' very restricted distribution — it is confined to the Uatumã River basin — combined with threats to that single system. The Uatumã has been profoundly altered by the Balbina hydroelectric dam, which flooded a vast area, fragmented the river, and changed downstream flow, oxygenation and sediment dynamics. For a rheophilic, flow-dependent fish known from nowhere else, such large-scale habitat modification is a serious and continuing threat, and the Endangered status underscores the conservation significance of this narrowly distributed endemic.