Taxonomy & naming
Awaous dayi was described by Philippe Keith and Marion I. Mennesson in 2026, in a revision of the genus Awaous (Teleostei: Oxudercidae) from Indo-Pacific islands published in the journal Cybium. That paper combined mitochondrial DNA sequencing (partial COI and ND2 genes) with morphological comparison to reassess species boundaries across the genus, recognising fifteen valid species in total and describing four new ones, three of them — including A. dayi — in that same publication. The Catalog of Fishes (Eschmeyer, CAS), the standing authority for valid fish names, lists the species as Awaous dayi Keith & Mennesson, 2026, placed in family Oxudercidae, subfamily Gobionellinae.
The holotype, and only known type specimen (registered MNHN-IC A-0011, held at the Muséum national d'Histoire naturelle, Paris), was collected from Orissa — now officially named Odisha — on India's northeastern coast. The full type description, including the diagnostic characters that separate A. dayi from its closest congeners, sits behind the journal's paywall; the characters used across the revision to distinguish species in the genus include the presence or absence of a white-edged black spot at the rear base of the first dorsal fin, caudal peduncle depth, body depth at the anal-fin origin, eye diameter, scale type and counts in the predorsal region and lateral line, presence of scales on the operculum and prepelvic area, and the position where the gill membrane attaches to the underside of the head — but which specific states apply to A. dayi is not confirmed here without access to the full text.
As in other Awaous, the species sits within the true gobies (Oxudercidae), a family defined by the fusion of the two pelvic fins into a single, cup-shaped sucker disc — the character that separates true gobies from the superficially similar sleepers and gudgeons (Eleotridae), whose pelvic fins remain separate.
Morphology
No maximum size, meristic counts, or colour description for Awaous dayi were accessible in the sources available for this article — the type description is published in a subscription journal and only the abstract, together with the Catalog of Fishes type record, could be consulted. What can be said with confidence is genus-level: Awaous species are moderately elongate, thick-lipped river gobies with a broad, somewhat depressed head, two separated dorsal fins, and eyes set high on the skull. The genus is diagnosed in part by the fusion of the pelvic fins into a sucker disc used to grip rock and gravel in flowing water.
The 2026 revision that described A. dayi separated the genus's Indo-Pacific species chiefly using the presence or absence of a dark, pale-edged spot on the rear of the first dorsal fin, relative body and caudal-peduncle depth, eye diameter, scale counts along the lateral line and predorsal area, whether those scales are ctenoid (rough-edged) or cycloid (smooth-edged), and scale coverage on the operculum, preoperculum, prepelvic region and pectoral-fin base. Those are the tools the authors used to tell A. dayi apart from its relatives; this article cannot confirm which specific values were recorded for this species without the full text, and reports none as fact.
Habitat
Awaous dayi is known from the Indian Ocean drainages of the Bangladesh and Odisha (formerly Orissa) region of northeastern India, per the Catalog of Fishes distribution record drawn from the original description. The holotype was collected in Odisha. The Catalog of Fishes lists the species' habitat as freshwater, brackish, and marine — the same three-part habitat classification given to essentially every other species in the genus, reflecting the amphidromous life cycle typical of Awaous: adults resident in rivers and estuaries, with a larval phase that passes through brackish and marine water.
No further habitat detail — substrate, elevation, water flow, or specific river names beyond the type locality — was available in the accessible sources. Other Awaous in the region typically occupy clear to turbid lowland and mid-elevation rivers with sand, gravel or rocky substrate, grading into brackish estuaries near the coast; A. dayi is presumed, but not confirmed, to follow the same pattern as a labelled genus-level generality rather than a documented fact specific to this species.
Feeding
No feeding data specific to Awaous dayi has been published in the sources accessible for this article. Across the genus, Awaous species are typically benthic omnivore-grazers that scrape filamentous algae, biofilm and organic detritus from rock, gravel and sand surfaces using their thickened lips and specialised jaw, supplementing that diet with small invertebrates taken from the substrate — a feeding mode associated with the thick, slightly protruding upper lip characteristic of the genus. Whether A. dayi shares this diet has not been directly documented and is stated here only as a genus-level expectation, not a confirmed fact about this species.
Mating
No mating behaviour has been documented for Awaous dayi specifically. Amphidromy — the life-history pattern in which adults breed in fresh or brackish water but the resulting larvae are swept to sea for a planktonic development phase — is the rule across Awaous and the wider Oxudercidae subfamily Gobionellinae to which the species is assigned, and its congeners typically breed with males defending a rock or gravel spawning site that a female is courted into. Whether A. dayi follows this pattern has not been confirmed in the literature accessible here; it is presented as a genus-level expectation only.
Breeding
No breeding record exists for Awaous dayi. In other Awaous species, the female deposits adhesive eggs in a rock crevice or on a cleaned hard surface, and the male guards and fans the clutch until hatching; the newly hatched larvae then drift downstream to the sea, where they spend a period of weeks to months as marine plankton before returning post-larvae recruit back into fresh water. This pattern is standard for amphidromous gobies of the genus and is offered here only as a genus-level expectation for A. dayi, not a documented observation. There is, unsurprisingly for a species described in 2026 from a single holotype, no captive-breeding record of any kind.
In the aquarium
Awaous dayi has no history in the aquarium trade. It was described in 2026 from a single type specimen collected for taxonomic research, not the ornamental fish trade, and there is no indication it has ever been exported or offered for sale. As with other Awaous, any future appearance in the hobby would almost certainly be as a wild-caught, amphidromous specialist unsuited to captive breeding: a large, roomy freshwater-to-brackish tank with strong filtration, high dissolved oxygen, a secure lid, and access to algae or biofilm to graze would be the baseline expectation drawn from the genus generally, not from any documented husbandry of this species. Prospective keepers should treat any such generalisation as speculative until species-specific information exists.
Conservation
Awaous dayi has not been evaluated by the IUCN Red List; as a species described in 2026, it postdates the most recent assessment cycles for the genus. No population or threat data specific to the species is available. Amphidromous gobies as a group are vulnerable to anything that severs the connection between river habitat and the sea — dams, barrages, and other barriers to fish passage prevent returning post-larvae from recolonising upstream habitat, and coastal and estuarine pollution or sedimentation degrades the nursery and adult habitat both. Whether any of these pressures affect A. dayi specifically in Odisha or Bangladesh is not documented in the sources available here.