Taxonomy & naming
Mogurnda adspersa was first described by the French naturalist François Louis de la Porte, Comte de Castelnau, in 1878, making it one of the earlier-described members of the Australian gudgeon fauna. The Catalog of Fishes (Eschmeyer, CAS) — the standard authority for valid names — places it in the genus Mogurnda and the family Eleotridae. Historical literature sometimes assigned eastern Australian gudgeons to Gobius or Eleotris, reflecting the taxonomic turbulence of the nineteenth century, but the genus Mogurnda has been stable in modern usage and is confirmed by the Catalog of Fishes.
The Eleotridae — sleepers and gudgeons — form the sister group of the true gobies (Gobiidae, Gobionellidae, Oxudercidae). The unifying character of the true gobies is the pelvic disc, a cup-shaped sucker formed by fused pelvic fins; eleotrids lack this fusion, their pelvic fins remaining free and separate. In the aquarium hobby the distinction is routinely ignored — Mogurnda, Tateurndina and Hypseleotris are all sold as 'gobies' — but the difference is real and meaningful: these fish have their own evolutionary history and care requirements that do not map onto Asian gobies (Rhinogobius, Stiphodon) or bumblebee gobies (Brachygobius).
Mogurnda as a genus name may derive from an Australian regional or indigenous source, though the precise etymology is not firmly established in the literature. The southern purplespotted gudgeon belongs to the same Australasian eleotrid assemblage as Hypseleotris (carp gudgeons), Oxyeleotris (sleeper gudgeons), and the closely related northern purplespotted gudgeon, Mogurnda mogurnda.
Morphology
Mogurnda adspersa is a small, somewhat elongate, benthic fish reaching around 3 in in standard length in the wild, though aquarium specimens commonly stay in the 1.5–2.5 in range. The body is cylindrical toward the head and compressed toward the tail, well-adapted to a life spent resting on and moving across the bottom. The head is broad and somewhat flattened, with a large mouth equipped for grasping prey.
Coloration is the species' strongest card. The base tone is a grey-olive or brownish-grey, and over this the fish is liberally scattered — 'spangled' — with small iridescent spots of blue, violet, red and purple, a pattern that shifts and glimmers in good light. The fins carry similar spotting and streaking. As with many eleotrids the species shows some sexual dimorphism: breeding males develop heightened colour intensity and may show bolder markings on the fins; females, when ripe, have a visibly fuller abdomen. The pelvic fins are clearly separate rather than fused, the defining structural character that distinguishes all Eleotridae from the true gobies.
Habitat
The southern purplespotted gudgeon is an Australian endemic found in the freshwater streams, creeks and rivers of eastern Australia, principally Queensland and New South Wales. It inhabits the shallower reaches of clear to lightly turbid lowland and foothill streams, typically over substrates of gravel, sand or leaf litter, where it spends its time on or close to the bottom in among cover such as submerged wood, rock, and aquatic vegetation.
These are temperate to warm-temperate freshwaters. The species tolerates a wide seasonal temperature range but is most active and healthy at 64–79 °F, with an optimum of around 68–77 °F, and is thus cooler-water than many of the tropical eleotrids. It thrives in near-neutral water in the pH 6.5–7.5 range and is primarily a freshwater fish — it is not a brackish-water species in the manner of Dormitator or Eleotris, and should not be kept with added salt. The species is adapted to moderate current and well-oxygenated conditions, consistent with life in moving Australian creek systems.
Feeding
Mogurnda adspersa is a benthic micro-predator, hunting by ambush and short burst rather than active pursuit. In the wild it takes small aquatic invertebrates — insect larvae, crustaceans, worms, small molluscs — from the substrate and among bottom cover. Like most eleotrids it is a sight-feeder that responds to movement; it is not an algae grazer or detritivore.
In the aquarium the same micro-predator instinct means it performs best on live and frozen foods: bloodworm (chironomid larvae), brine shrimp, daphnia, cyclops, small earthworm sections and similar items. It is notably reluctant to accept dry flake or pellet food, and fish kept exclusively on prepared diets tend to lose condition, refuse to breed, and decline over time. Feeding live or thawed frozen food every day or every other day, varied across several food types, is the standard approach among specialist keepers. Once settled and well-fed it is a confident feeder that will take food from tongs or from the surface of the substrate.
Mating
Mogurnda adspersa is a resident freshwater cave-spawner — a breeding strategy typical of the small Australasian eleotrids and quite different from the amphidromous pattern seen in many stream gobies (Stiphodon, Sicyopterus) whose larvae must develop at sea. The whole reproductive cycle of M. adspersa takes place in fresh water, which is what makes captive breeding possible.
Males are territorial and will hold a preferred cave, hollow, crevice or piece of submerged debris against rivals. A ripe female, recognisable by her distended abdomen, is courted in and around the cave entrance; the male intensifies his iridescent spotting and uses fin displays to attract and direct her. Because males are aggressive toward one another — and sometimes toward females outside of spawning — the aquarium should provide enough space for territories, with line-of-sight breaks and multiple shelters.
Breeding
Once a female is accepted into the cave, she lays a clutch of adhesive eggs on the roof, wall or floor of the chosen site — the number varies with the female's size and condition but can be considerable. The female's role ends with spawning; from that point the male takes complete charge, guarding the cave against any perceived threat and fanning the egg mass continuously with his pectoral and tail fins to maintain oxygenation and remove detritus. Incubation takes roughly a week to ten days depending on temperature.
The newly hatched fry are small and require micro-foods at first — infusoria, commercially prepared fry foods, or rotifers — before advancing to newly hatched brine shrimp nauplii and microworm as they develop. Breeders find that moving the egg-bearing cave to a separate rearing vessel immediately after spawning can improve survival, removing the male's potential stress on the fry once they hatch. Because M. adspersa is a resident breeder with attentive male parental care and does not require a marine larval phase, it can be bred consistently in a well-managed aquarium when feeding and water quality are maintained.
In the aquarium
The southern purplespotted gudgeon is a specialist fish rather than a community staple. It is best housed in a species tank or with robust, non-nippy companions that share its temperate water requirements, because it needs cooler conditions than most tropical community fish and is easily outcompeted at feeding time. A tank in the 15–25 US gal range suits a pair or small group, furnished with sand or fine gravel, smooth flat stones or slate, driftwood and a generous supply of caves and shelters — PVC pipe sections, coconut shell halves, upturned terracotta pots. Males will fight for prime cave sites, so provide more caves than males.
Temperature should be held at 64–77 °F with a winter dip if seasonal cycling for breeding; pH 6.5–7.5; good filtration and regular water changes are important as it is intolerant of poor water quality. It must be fed live or frozen invertebrate foods — relying on flake alone will result in a slowly declining fish. A tight-fitting lid is advisable, as most benthic gobies and gudgeons are capable of leaving the water. Rarely imported and seldom offered for sale outside of Australia, it is a rewarding fish for the specialist willing to meet its dietary and environmental needs.
Conservation
Mogurnda adspersa has not been formally assessed on the IUCN Red List and is recorded here as Not Evaluated. The species is an eastern-Australian endemic confined to the streams and rivers of Queensland and New South Wales, a range that is entirely within a region subject to ongoing pressures: water extraction for agriculture, stream channelisation, introduced predators such as bass and gambusia, and the effects of periodic drought intensified by a changing climate. Localised populations may be vulnerable to these cumulative impacts even if the species as a whole is not currently in crisis.
In the aquarium trade the fish is scarce outside Australia — it is rarely exported and is not commercially mass-produced. Most specimens in the hobby are wild-collected or bred by specialists, which keeps collection pressure low. For keepers outside Australia, sourcing from captive-bred lines where available is the responsible approach. Inland water quality and connectivity in eastern Australian streams remain the most important conservation axes for this and other native gudgeons.