Taxonomy & naming
Harttiella longicauda was described by Raphaël Covain and Sonia Fisch-Muller in 2012, in the journal Cybium (volume 36, number 1, pages 115–161), as part of a revision of the genus Harttiella from the Guianas. The Catalog of Fishes (Eschmeyer, CAS) treats Harttiella longicauda Covain & Fisch-Muller, 2012 as a valid name.
The genus Harttiella belongs to the subfamily Loricariinae, within the tribe Harttiini — the slender, elongate loricariids whose bodies taper to a thread-like tail. Harttiella is a small genus of miniature species restricted to the upland streams of the Guiana Shield, several of which (including this one) have narrow, single-massif distributions.
Morphology
Harttiella longicauda is a miniature loricariin reaching a maximum recorded length of about 2 in standard length. The body is elongate and slender, and the species is distinguished — as its name indicates — by an elongate caudal peduncle.
Published meristics give a dorsal fin with 7 soft rays, and an anal fin with 1 spine and 5 soft rays. The species frequently bears small preanal plates. As is typical of the subfamily, the body is encased in rows of bony scutes. No data on sexual dimorphism is published in the sources consulted.
Habitat
The species is endemic to mountainous areas in the Trinité and Balenfois massifs of northern French Guiana, in South America. It is a demersal, freshwater, tropical fish of mountain streams.
In the Trinité Mountains, H. longicauda occurs alongside other Guiana Shield loricariids, including Guyanancistrus aff. brevispinis, Lithoxus planquettei, and Rineloricaria aff. stewarti, among others. Its trophic level is estimated at 2.7, consistent with a grazing rather than predatory habit.
Feeding
No detailed feeding study is published for Harttiella longicauda. Its estimated trophic level of 2.7 and its loricariin body plan are consistent with a benthic grazer feeding on algae, biofilm (aufwuchs), and associated fine detritus rasped from rock surfaces in its fast-flowing mountain habitat. Specific dietary data is sparse.
Mating
No data on courtship or mating behaviour has been published for this species.
Breeding
No breeding data has been published for Harttiella longicauda. Loricariins as a group are generally substrate spawners with paternal egg care, but no reproductive observations specific to this species are available in the sources consulted.
In the aquarium
Harttiella longicauda is not a hobby species: it is a tiny, narrowly endemic fish of cool, fast upland streams with no record of aquarium maintenance in the sources consulted. Its restricted range and Vulnerable conservation status make it unsuitable and inappropriate as an aquarium subject. Any inference about captive requirements would be speculative.
Conservation
The IUCN Red List assessed Harttiella longicauda as Vulnerable (VU) under criterion B1ab(iii), with the assessment dated 14 January 2021. The species is not evaluated under CITES.
The Vulnerable listing reflects its very restricted distribution, confined to the Trinité and Balenfois massifs of northern French Guiana. Narrowly endemic upland-stream fishes of this kind are especially sensitive to localised habitat disturbance — including changes to stream flow, sedimentation, and forest cover within their single-massif ranges.