Taxonomy & naming
Gastromyzon psiloetron was described by Tan in 2006 in his revision of the Bornean torrent loaches. The type locality is a stream next to the Birai Field Station, a feeder of the Enggeng, which drains to the Bahau River in the Kayan basin, at 1,148 ft elevation. The Catalog of Fishes (Eschmeyer, CAS) is the authority for the valid name.
Morphology
Typical of Gastromyzon: a flattened body and a broad sucker formed by the paired fins. FishBase gives a maximum of 3.5 in SL. Colour details have not been compiled here.
Habitat
Small, fast upland streams with clear water over rock; the type locality lies at 1,148 ft elevation in the Kayan drainage of Kalimantan Timur. FishBase lists the species as freshwater and demersal, with a range covering the Kayan and Mahakam basins in East Kalimantan and the Kapuas basin in West Kalimantan.
Feeding
Gastromyzon graze biofilm and small invertebrates from stone surfaces. No dietary study of this species has been published.
Mating
Courtship has not been described for this species.
Breeding
Spawning has not been described, in the wild or in captivity.
In the aquarium
Treat it as any Bornean Gastromyzon: cool, well-oxygenated, fast-flowing water, a mature biofilm-covered rockscape, and a group of its own kind. Its larger adult size, up to 3.5 in SL, calls for more room than the smaller species. Temperature and pH ranges have not been published for it.
Conservation
The IUCN assessed Gastromyzon psiloetron as Least Concern in 2019, meaning it is not currently considered at risk. Hillstream loaches remain sensitive to siltation and logging in their catchments.