Taxonomy & naming
Sicyopus discordipinnis is a true goby of the family Oxudercidae, placed in the Sicydiinae, the amphidromous stream gobies of Indo-Pacific islands. The Catalog of Fishes lists it as valid under the authority Watson, 1995. The type locality is given there as: Letak Creek, 25 kilometers southeast of Wewak, Papua New Guinea.
Morphology
Sicydiine gobies have the pelvic fins fused into a cup-shaped sucker disc, which lets them hold position on rock in fast current and climb wet rock faces on the way upstream. Males in this group are usually more colourful than females. FishBase gives a maximum of 1 in SL for this species; a detailed colour description has not been compiled here.
Habitat
FishBase says the species inhabits clear, swift, high-gradient streams with a bottom of boulders and gravel, at elevations of about 1,148–1,640 ft. It is listed as freshwater and benthopelagic, and occurs in northern New Guinea and on New Hanover and Bougainville. Measured water chemistry has not been published.
Feeding
Sicyopus species are generally understood to take small invertebrates rather than graze algae. The diet of this species has not been described specifically.
Mating
Mating has not been described for this species. In better-studied sicydiines, males hold small territories on stream rock and court females at a nest site.
Breeding
Sicydiine gobies are amphidromous: eggs are laid in fresh water, the larvae drift to sea, and the post-larvae return to rivers months later. Details specific to this species have not been published. It cannot be assumed to breed in a closed freshwater aquarium, and trade fish are wild-collected.
In the aquarium
Species in the trade under this name are demanding. They need cool to moderate, very clean, strongly oxygenated water, brisk flow, rock surfaces with mature biofilm, and a tightly closed lid. Husbandry for Sicyopus discordipinnis itself has not been documented, so general sicydiine practice is the only guide. Identity of fish sold under this name should be treated with caution.
Conservation
The IUCN assessed Sicyopus discordipinnis as Least Concern in 2019, meaning it is not currently considered at risk. Like other amphidromous gobies, it depends on unobstructed streams down to the sea, and dams, weirs and stream degradation are threats to the group.