Taxonomy & naming
Harttia dissidens was described by Rapp Py-Daniel and Oliveira in 2011, from a type series collected at the Rio Tapajós near Pimental (approximately 4°35'S, 56°15'W), Pará State, Brazil. The species has no synonyms.
The genus Harttia belongs to the subfamily Loricariinae, the slender, elongate 'whiptail' loricariids distinguished by their flattened bodies and long, tapering caudal peduncles. Harttia is a species-rich genus of the rheophilic streams and rapids of eastern South America, and the lower-Amazon members — including dissidens — were treated together in the 2011 revision of the Tapajós and neighbouring drainages.
Morphology
Harttia dissidens reaches about 6 in in standard length, making it one of the larger species in its lower-Amazon group. In keeping with the genus it has the characteristic Loricariinae form: a strongly depressed head and body, broad pectoral region, and a long, slender, tapering tail — the build of a fish adapted to holding position on rock in moving water.
Detailed published colour notes and meristic diagnostics are confined largely to the original 2011 description, and no reliable account of sexual dimorphism has been published for this species.
Habitat
The species is restricted to the Tapajós River basin in the lower Amazon, Pará State, Brazil. It is a freshwater, demersal, tropical fish associated with rocky rapids habitat — the clear, fast-flowing water typical of rheophilic Harttia.
The type locality near Pimental lies on the Tapajós at the very stretch targeted for hydroelectric development. Specific field measurements of temperature, pH, and conductivity for this species are not published, but the rapids setting implies well-oxygenated, flowing water over stone.
Feeding
No dedicated dietary study has been published for Harttia dissidens. Like other rheophilic loricariines of rocky rapids, it is presumed to graze the biofilm and associated micro-invertebrates coating submerged stones. This is inference from the genus and habitat rather than documented diet for this species.
Mating
No data on courtship or mating behaviour has been published for this species.
Breeding
No breeding reports or reproductive data have been published for Harttia dissidens. Many Loricariinae are egg-clutch guarders with paternal care, but no such observations are documented for this species specifically.
In the aquarium
Harttia dissidens is rarely if ever seen in the ornamental trade, and reliable husbandry data is absent. As a rheophilic rapids species it would in principle require strong current, high oxygenation, clean water, and a stony substrate — the demanding conditions associated with fast-water whiptail loricariids. Any keeping guidance remains inferential, and the species is far better documented as a scientific specimen than as an aquarium subject.
Conservation
The IUCN Red List assessed Harttia dissidens as Vulnerable, last assessed in 2018. The species is restricted to the Tapajós basin and is tied to rapids habitat threatened by hydroelectric development — notably the São Luiz do Tapajós and related dam projects, which would inundate or fundamentally alter the fast-water stretches the species depends on. Its narrow range and habitat specialisation are the principal drivers of its threatened status.