Taxonomy & naming
Oxyeleotris lineolata was originally described by the Austrian ichthyologist Franz Steindachner in 1867 under the combination Eleotris lineolatus, and its subsequent taxonomic history has been tangled. The species was at various times placed in Bunaka as Bunaka herwerdenii and in Oxyeleotris as Oxyeleotris herwerdenii before those names were synonymised with O. lineolata under the authority of the Catalog of Fishes (Eschmeyer, CAS). GBIF confirms the valid combination as Oxyeleotris lineolata (Steindachner, 1867), placed in the family Eleotridae and order Gobiiformes.
The critical taxonomic point for anyone coming to this fish from the goby hobby is that Eleotridae are not true gobies. The true gobies — family Gobiidae and close relatives Gobionellidae and Oxudercidae — possess pelvic fins that are fused into a cup-shaped sucker disc; eleotrids keep their pelvic fins separate, and that structural difference defines the lineage. The genus Oxyeleotris is placed within the Butidae (sometimes treated as a subfamily of Eleotridae), a broadly Australasian and Indo-Pacific assemblage of sleepers. The lined sleeper is thus a gudgeon in the technical sense, though the name 'sleepy cod' in Australian angling culture reflects its sluggish, bottom-hugging behaviour rather than any kinship with the cods.
Morphology
Oxyeleotris lineolata is a large, robust, cylindrical fish with the typical sleeper body plan: a broad, slightly depressed head, a wide mouth, and a body tapering to a rounded caudal fin. FishBase records a maximum standard length of 17.5 in and weights of up to 3 kg, though fish of 6–10 in are much more typically encountered. The fins are characteristic of the genus: two separate dorsal fins (the first with 7 spines, the second with 8–9 soft rays), an anal fin with 1 spine and 7–9 soft rays, and the diagnostic separate pelvic fins that immediately separate this fish from any true goby.
The common name 'lined sleeper' refers to the pattern: a pale brown to olive-grey background is crossed by a series of dark longitudinal stripes or rows of blotches along the flanks, often with a faint pale stripe below the lateral line. Colouration is variable and can shift with mood or background. The species is a facultative air-breather, capable of gulping air when dissolved oxygen drops in stagnant water, an adaptation useful in the billabongs it inhabits during the dry season. Sexual dimorphism is subtle externally, with the genital papilla being the most reliable indicator: broad and flattened in females, triangular and pointed in males.
Habitat
In its native range — the Durack River in the Kimberley region of Western Australia east through the rivers of northern Queensland to Cape York, and south through the Fitzroy River (Queensland), as well as the Fly River drainage of Papua New Guinea — the lined sleeper occupies warm freshwater rivers, creeks, and billabongs. It favours quiet or slow-flowing water with abundant cover: beds of aquatic vegetation, submerged logs, root masses and snag debris, and shallow, turbid margins. It is a demersal fish, spending most of its time on or very close to the bottom.
This is a strictly freshwater species; unlike some eleotrids (Dormitator, Eleotris) that regularly venture into brackish estuaries, O. lineolata is documented from fresh water only and does not require added salt. FishBase gives a temperature range of 68–82 °F, consistent with its tropical and subtropical distribution across northern Australia and southern New Guinea. Billabongs — the oxbow lakes and backwaters cut off from main river channels during the dry season — are particularly important habitat, providing warm, still water and prey concentrations that suit the species' ambush feeding strategy.
Feeding
Oxyeleotris lineolata is a sit-and-wait micro-predator and opportunistic piscivore. Fishes of Australia records its diet as insects, small fishes and crustaceans, reflecting a broad carnivorous habit that scales with body size: smaller fish take mostly insects and invertebrates, while larger individuals regularly consume small fishes and prawns. It does not graze algae and is not a scavenger of plant matter.
In the aquarium this translates to a preference for live and frozen meaty foods. Smaller specimens accept bloodworm, brine shrimp, daphnia and other invertebrate feeds; larger fish readily take whole small fish, krill and prawn pieces. Dry flake and pelleted foods are typically refused or ignored, especially initially — most keepers find success transitioning larger individuals onto good-quality sinking carnivore pellets only after extended conditioning on frozen foods. Being honest about this feeding requirement is a key care point: an O. lineolata placed in a community tank and expected to eat flake will slowly starve.
Mating
Oxyeleotris lineolata is a resident freshwater substrate-spawner. There is no amphidromous larval stage in the marine environment; the complete reproductive cycle takes place in fresh water, which is what makes captive breeding possible in a suitably large system. Spawning in the wild is seasonal: Fishes of Australia records the main period as October to February, coinciding with the Australian spring and early summer warm-up. The ScienceDirect breeding study found that spawning is triggered when water temperatures exceed 75 °F for at least three consecutive days, and that females can spawn up to ten times per season.
Males establish and defend nest sites — rock crevices, the undersides of submerged logs, and hollow root masses — and court ripe females to these sites. In the aquarium males become territorial around potential spawning sites and will spar with rival males; providing large caves, pipes or overturned containers of appropriate size gives the male a focus for his territory. Courtship peaks in the early morning hours, with field studies noting most spawning occurs between 05:00 and 10:00.
Breeding
The female lays her eggs on the underside of a hard surface within the nest cavity — the roof of a crevice, the underside of a log, or similar — where they adhere in a single layer. The ScienceDirect study found a mean of approximately 43,000 eggs per spawning event, with total seasonal fecundity running to several hundred thousand eggs across multiple spawnings. The female attends the eggs briefly post-spawning, but it is the male who takes primary responsibility for the clutch: he guards the nest against intruders and fans the eggs with his fins to keep them oxygenated and free of debris. Hatching takes 3–7 days depending on temperature, with 5–7 days typical at natural temperatures. Larvae are initially very small, feeding on planktonic particles of 100–250 µm in the days after yolk-sac absorption.
In the aquarium, successful breeding requires a large tank (given the adult size, a tank of 55 US gal or more is appropriate for a pair), warm clean water near the upper end of the temperature range, and a suitable cave or nest structure. The male's parental behaviour — active fanning and guarding — means that the eggs are well protected if the tank is otherwise stable. Fry need appropriately sized live foods at first; newly hatched brine shrimp and small live invertebrates suit them once past the yolk-sac stage. The high fecundity means that a successful spawning can yield thousands of fry, which requires planning for grow-out space.
In the aquarium
The lined sleeper is not a fish for a small or community tank. Its maximum size of 17.5 in and common adult size of 8–10 in mean it needs a genuinely large aquarium — a minimum of 55 US gal for a single adult, larger for a pair — and any tankmate small enough to swallow will be eaten. It is a predator and should be housed accordingly, either alone or with species of comparable or larger size. It does best in warm, clean fresh water (68–82 °F) with a soft, sandy or fine-gravel substrate that lets it settle its belly against the bottom, and plenty of cover in the form of large caves, pipe sections, or overturned pots to satisfy its need for a dark retreat.
This is an essentially still-water fish; strong current is not needed and may stress it. Filtration should be adequate for the bioload of a large predatory fish but gentle in output. The lined sleeper is a sedentary species that may barely move for hours at a time, then strike with sudden speed — the 'sleepy' in its common name is apt. It needs no added salt and is not a brackish species. The primary care requirements are a tank large enough to house it properly, a diet of live or frozen meaty foods (not dry flake), suitable cave structures for shelter and eventual breeding, and a lid — like most eleotrids it is capable of leaving the water briefly and a good cover is essential. Enthusiasts with the space and commitment to its carnivorous diet find it a fascinating, long-lived and characterful fish.
Conservation
Oxyeleotris lineolata was assessed as Least Concern on the IUCN Red List in 2021 by Ebner, Kerezsy, Brooks and Larson. The assessment notes that the species is common within its native range across northern Australia and southern New Guinea and that its overall status is stable. It is an important recreational angling species — known as 'sleepy cod' in the Queensland fishing community — and has attracted interest as an aquaculture candidate given its fast growth and palatability.
The main conservation nuance flagged by the 2021 assessment is translocation. Oxyeleotris lineolata has been moved outside its native Queensland and Western Australian drainages, and in basins where it has been introduced it can impact native fish communities through predation and competition. Within its natural range, the pressures it faces are those common to tropical freshwater fish across northern Australia: habitat modification from altered river flows, degraded riparian vegetation, and the well-documented competitive and predatory effects of introduced species such as tilapia and carp. The species does not rely on wild collection for the aquarium trade to any significant extent, as it is not widely kept relative to its angling profile, and no trade-driven decline has been reported.