Taxonomy & naming
Oxyeleotris selheimi was described by William Macleay in 1884 from material taken at the Palmer River in north Queensland, which remains the type locality. The Catalog of Fishes (Eschmeyer, CAS) places it in the genus Oxyeleotris within the family Eleotridae — the sleepers and gudgeons — not among the true gobies. This distinction matters: the true gobies (Gobiidae and the closely related Gobionellidae and Oxudercidae) carry their pelvic fins fused into a cup-shaped sucker disc that can anchor them to rocks in fast current; the eleotrids, including all the Oxyeleotris, keep their pelvic fins separate. One look at the underside confirms which lineage you are dealing with.
Oxyeleotris is the largest genus of eleotrids and is centred on northern Australia and New Guinea, with several species extending into the Indo-Pacific. O. selheimi sits at the large end of the Australian sleepers alongside O. lineolatus; it has previously appeared in the literature under various combinations as the genus boundaries and regional taxonomy have been revised, but Oxyeleotris selheimi (Macleay, 1884) is the current valid name as recognised by the Catalog of Fishes and the Australian Faunal Database (AFD).
Morphology
The blackbanded gudgeon is a robust, elongate fish with a broad, slightly depressed head, a large terminal mouth and two separate dorsal fins — a body plan built for ambush rather than sustained open-water pursuit. Maximum recorded size is 21.5 in standard length, with fish of 12 in common in rivers and billabongs; it is among the largest freshwater fish regularly encountered by anglers and naturalists in northern Australia. The body is dark brown on the dorsal surface, grading to a lighter cream-buff on the belly, with a series of dark brown vertical bars or blotches on the flanks.
As in all eleotrids, the pelvic fins remain separate and are not fused into any kind of adhesive disc — the diagnostic character that separates this family from the true gobies. The scales are ctenoid (rough-edged), the lateral line is well-developed, and the large eyes are set high on the head, consistent with a fish that hunts by sight in low-light conditions. Sexual dimorphism is not conspicuous externally, though sexually ripe females may be visibly fuller-bodied.
Habitat
Oxyeleotris selheimi inhabits freshwater rivers, creeks and billabongs across tropical and subtropical northern Australia, from the Fitzroy River system of the Kimberley region in Western Australia east to the Endeavour River near Cooktown in north Queensland, and extending into southern Papua New Guinea. The type locality is the Palmer River of Cape York Peninsula. It is a strictly freshwater species; there is no indication of estuarine or brackish tolerance of the kind seen in some other Oxyeleotris species.
Within freshwater systems it shows a clear preference for slow-flowing or still water with structural complexity: undercut banks, submerged woody debris, dense aquatic vegetation and shaded billabong margins. It is a benthic fish, spending the day resting in cover and becoming active at night when it moves into open water to hunt. Water temperatures across its range are warm for most of the year, and it experiences a marked seasonal dry-season reduction in river flow and a wet-season flood pulse that drives spawning activity.
Feeding
O. selheimi is a carnivore with a trophic level of approximately 3.9 — placing it firmly in the upper tier of the food web in the freshwater systems it inhabits. It is a nocturnal ambush predator, taking fish, freshwater crustaceans and aquatic insects, relying on its large mouth and patient, sit-and-wait strategy to secure prey. Smaller gudgeons forage on invertebrates and small fish; larger individuals shift toward a diet dominated by fish.
In the aquarium this translates to a fish that needs meaty, live or frozen foods: feeder fish (with the usual biosecurity caveats), prawns, large earthworms, mussel, and pieces of fresh fish. It is unlikely to accept dry pellets readily, and a diet of low-quality food leads to condition loss. Any fish small enough to fit in its mouth will be eaten, which sets the parameters for tankmates.
Mating
Oxyeleotris selheimi is a resident freshwater spawner with male parental care, breeding entirely within the freshwater systems it inhabits. In the wild, spawning is seasonal and associated with the tropical wet season (October to February in northern Australia), when rising water levels and increasing temperatures appear to trigger reproductive activity. This is consistent with the broader pattern among the resident Australian eleotrids and contrasts sharply with the amphidromous gudgeons of the Pacific, whose larvae must develop at sea.
Conditioned pairs in the wild select hard substrate surfaces on which to deposit eggs — flat rocks, firm sediment, submerged timber or similar firm, sheltered sites near cover. Courtship behaviour has not been described in detail for this species, but the general eleotrid pattern of male territory establishment and female attraction applies. Males become defensive of chosen spawning sites as water temperatures and photoperiod shift toward the breeding season.
Breeding
Spawning has been documented in detail by researchers working on Australian native fish. Females deposit 35,000 to 170,000 eggs on hard substrates — a very large clutch relative to the smaller gudgeons, which reflects the species' large adult size. The eggs measure approximately 0.5 in in length by 0.5 in in width and are adhesive, sticking to the substrate surface in a single layer. After deposition the female's role is complete: the male guards the clutch, fanning the eggs with his fins to ensure oxygenation and removing any unfertilised or fungused eggs. Hatching occurs within three to seven days at tropical water temperatures.
Because the entire reproductive cycle takes place in fresh water and the male provides genuine parental care, O. selheimi can in principle be bred in a very large, well-managed aquarium — unlike the amphidromous gobies that cannot. However, the fish's large adult size (12–21.5 in), territorial aggression during spawning, and the scale of its natural habitat mean that home-aquarium breeding is rarely attempted or documented. The seasonal flood-pulse cue and the enormous clutch sizes suggest that replicating the conditions for successful spawning is non-trivial.
In the aquarium
The blackbanded gudgeon is kept by Australian native-fish enthusiasts rather than the general community-aquarium hobby, and the adult size of 12–21.5 in explains why: a large tank of at least 105–160 US gal is required for a single adult, with filtration to match a heavily feeding apex predator. It is a nocturnal species that needs substantial cover — large pieces of driftwood, rock caves and shaded hiding areas are essential for the fish to behave naturally and reduce stress.
Temperature should be maintained in the warm-tropical range appropriate to its northern Australian origins, and water quality should be clean and well-oxygenated. Any fish or invertebrate small enough to be swallowed will be eaten; O. selheimi should be kept only with fish of similar or greater size, and even large tankmates must be robust enough to tolerate a large, occasionally territorial predator. It is not a community fish and should not be housed with peaceful small species. Its diet requires regular meaty foods — live, fresh or frozen — and it is unlikely to accept pellets or flake without sustained effort at weaning. A covered tank is advisable, as large eleotrids can and do jump.
Conservation
Oxyeleotris selheimi was assessed as Least Concern on the IUCN Red List by Brooks and Kerezsy in 2019. The species has a reasonably broad distribution across northern Australia's tropical freshwater systems and into Papua New Guinea, and it is not subject to significant targeted commercial take. Its population doubling time is estimated at 1.4–4.4 years, indicating medium resilience to pressure — consistent with a large-bodied fish with high fecundity.
The main threats to this and other large Australian freshwater fish are habitat degradation through riparian clearing, hydrological changes associated with water extraction and agricultural development, altered wet-season flood regimes, and the spread of introduced species such as tilapia and barramundi-farming escapees into northern river systems. Within its core Kimberley and Cape York range, many rivers remain in relatively good condition compared with southern Australian systems, which helps maintain this species' Least Concern status. It is also a targeted recreational angling species in parts of its range, though catch-and-release practices are common and there is no evidence of unsustainable angling pressure.