Taxonomy & naming
Mogurnda oligolepis was described by Gerald R. Allen and Douglass F. Hoese in 1991 on the basis of specimens from the Kimberley District of Western Australia. The type locality is Mogurnda Creek, a tributary of the Drysdale River within Drysdale River National Park, at approximately 15°03'S, 126°52'E — an isolated upland creek in the remote north-west of the continent. The species epithet oligolepis is Greek for 'few scales', a reference to the reduced scale count that distinguishes this species from its congeners.
The Catalog of Fishes (Eschmeyer, CAS) places Mogurnda oligolepis in the family Eleotridae — the sleeper gobies and gudgeons — not in the Gobiidae. This distinction matters: the fish is sold and searched for as a 'gudgeon', which is the accurate vernacular. True gobies (Gobiidae and their relatives Gobionellidae and Oxudercidae) carry their pelvic fins fused into a sucker disc; Eleotridae keep the fins separate. Mogurnda sits in the same Australasian gudgeon assemblage as the purple-spotted gudgeon (Mogurnda adspersa), the carp gudgeons (Hypseleotris) and the large sleepers (Oxyeleotris) — a lineage rooted in Australia and New Guinea rather than the Asian or American goby radiations.
The common name 'False-spotted Gudgeon' has been used in some Australian literature to distinguish this Kimberley-restricted species from the broader-ranging purple-spotted gudgeon M. adspersa.
Morphology
Mogurnda oligolepis is a slender, moderately compressed gudgeon that attains at least 3 in standard length. Like other Mogurnda it has two separate dorsal fins — the first short and spiny, the second soft-rayed and longer — and the characteristic eleotrid pelvic fins that stay apart rather than fusing into a disc. The body is pale to brownish, with a pattern of spots or blotches that gives rise to both the scientific epithet and the 'false-spotted' common name; the markings can be vivid under good light but are cryptic in the dappled, vegetated habitats the fish frequents.
Sexual dimorphism in the genus Mogurnda is subtle compared with some other eleotrids, but males in breeding condition typically display more intense colour and may develop slightly more extended fins. The sucker disc that would identify a true goby is absent — the paired, unfused pelvic fins are the easiest field and aquarium character separating this fish from any true goby of similar appearance.
Habitat
Mogurnda oligolepis is endemic to the Kimberley region of Western Australia, occurring west of the Pentecost River. Its range centres on the river systems of the Drysdale River National Park and surrounding catchments — among the least-disturbed tropical river systems in Australia. Within that range it inhabits creeks, billabongs and rocky pools, favouring calm or slow-moving water with submerged aquatic vegetation, root masses and structure near the substrate. It is a benthic, benthopelagic fish that stays close to the bottom.
This is a purely freshwater species with no dependence on estuarine or marine habitats, and it is not amphidromous — every stage of its life cycle takes place in fresh water. The Kimberley experiences a strongly seasonal climate, with a pronounced wet season (November–April) during which water levels rise dramatically and habitat connectivity increases, and a dry season during which fish are concentrated in deeper pools and billabongs. Water chemistry data specific to M. oligolepis is sparse in the literature, but Kimberley river water is generally warm and relatively clear, with temperatures typically in the range of 72–90 °F across seasons.
Feeding
Mogurnda oligolepis is a micro-predator. Like other small Mogurnda it forages among submerged roots, vegetation and the substrate for small crustaceans, insect larvae and aquatic invertebrates. It hunts by sight and ambush from cover — a typical gudgeon feeding strategy — rather than picking at algae or scavenging organic particles from the water column.
In the aquarium this translates to a diet of small live and frozen foods: bloodworm, brine shrimp, daphnia, small chironomid larvae and similar invertebrate prey. Like most small eleotrids it is likely to ignore or refuse dry flake foods, at least initially. Conditioning breeding pairs requires high-quality live or frozen feeds. Its mouth is proportionate to its body size, so food items should be sized accordingly.
Mating
Mogurnda oligolepis is a resident freshwater spawner with male parental care — the strategy consistent across the Mogurnda genus. Males establish and defend a territory around a suitable spawning site: a cave, crevice, rock overhang, hollow piece of wood or dense root mass. When in breeding condition the male courts females in the vicinity, displaying his colours and posturing at the entrance to the chosen site.
Because this species completes its entire life cycle in fresh water — unlike the amphidromous gudgeons such as Eleotris or Dormitator that release larvae to the sea — pairs can form and breed through a normal tropical aquarium wet-dry seasonal simulation or under stable, warm freshwater conditions. A ripe female is typically fuller-bodied and enters the spawning site to deposit eggs alongside the male.
Breeding
Breeding in Mogurnda oligolepis follows the pattern documented for the genus Mogurnda: the female deposits adhesive eggs firmly attached to a hard substrate inside the cave, crevice or other chosen site, and then largely withdraws. The male remains at the site, guarding the clutch and fanning the eggs with his fins to maintain oxygenation and prevent fungal growth. At warm tropical temperatures typical of the Kimberley — roughly 79–86 °F — eggs hatch in approximately three to nine days, consistent with data from the closely related M. adspersa.
The newly hatched fry are free-swimming within a day or two of hatching and require appropriately small first foods — infusoria or commercial fry foods initially, graduating to newly hatched brine shrimp nauplii. Because the parents do not consume the eggs and the male provides attentive care, breeding in a mature, well-planted aquarium with suitable cave sites is achievable without removing the eggs, though separating the cave to a rearing vessel after spawning is an option for higher fry survival. The species is not widely kept or bred in captivity, so published aquarium breeding accounts are limited.
In the aquarium
Mogurnda oligolepis is rarely seen in the trade outside Australia, where its Kimberley origin and restricted range make it a specialist's fish. Any specimens in the hobby are most likely wild-collected, since captive breeding of this species at scale has not been established. For those who do keep it, the requirements are straightforward: warm, clean fresh water (no salt), a covered tank to prevent jumping — eleotrids are capable jumpers — plenty of bottom structure in the form of caves, rocks, PVC pipe and submerged roots, and a diet of small live and frozen invertebrate prey rather than flake.
Males may be territorial toward one another, so multiple males need sufficient cave territory and visual breaks. The species is best kept in a small group or pair in a species tank or alongside other small, non-aggressive Australian natives. Tank size should be matched to the fish's adult length of around 3 in — a footprint of 23.5–31.5 in is a reasonable minimum for a pair. Water temperature in the range of 72–86 °F covers both the cooler dry-season pools and the warmer wet-season conditions of the Kimberley, and a seasonal temperature shift may assist conditioning for breeding. No salt or brackish conditions should be used.
Conservation
The IUCN Red List assessed Mogurnda oligolepis as Least Concern in 2019 (assessor: Moore). The species' range is centred on the Kimberley region of north-western Australia — one of the continent's least-disturbed large tropical catchments — and it occupies a relatively broad area of suitable habitat across the western Kimberley river systems, west of the Pentecost River. The intact catchment condition of much of its range is the primary reason for the Least Concern designation.
Nonetheless, as a regional endemic restricted to a specific part of the Kimberley, the species remains vulnerable to catchment-scale threats: altered dry-season water flows, water extraction from billabongs, and the progressive spread of feral animals (pigs, cattle) that degrade riparian vegetation and disturb the shallow, vegetated billabong margins the fish favours. Invasive fish species, particularly tilapia (Oreochromis spp.) and other introduced species steadily encroaching into Kimberley catchments, represent a longer-term threat to all native freshwater fish in the region. Australia's federal government lists the Kimberley as a biodiversity hotspot and numerous freshwater fish in the region are subject to monitoring programs.