Taxonomy & naming
Periophthalmus argentilineatus was described by the French zoologist Achille Valenciennes in 1837 and has remained in the genus Periophthalmus, the core mudskipper genus, ever since. The Catalog of Fishes (Eschmeyer, CAS) — the authority for valid names — places the genus in the family Oxudercidae, subfamily Oxudercinae, a lineage of highly derived amphibious gobies whose closest aquatic relatives are the ordinary estuarine gobies of the family Gobiidae.
This is unambiguously a true goby. True gobies (families Gobiidae, Gobionellidae, and Oxudercidae) are distinguished from the unrelated sleepers and gudgeons (family Eleotridae) by a single anatomical character: in true gobies the pelvic fins are fused into a cup-like sucker disc. In mudskippers that disc also functions as the third point of a land-locomotion tripod alongside the stiffened pectoral fins. Sleeper gobies and gudgeons keep their pelvic fins separate — an easy distinction that this section is careful to make.
The genus Periophthalmus is among the most species-rich in the mudskipper group and spans a broad range from tropical West Africa east to Oceania. Periophthalmus argentilineatus falls within the core Indo-West Pacific radiation and was historically confused with several closely related species before modern revisions clarified its limits. The common name 'grey-spotted mudskipper' is encountered alongside 'barred mudskipper', both referring to the spotted and barred pattern on the dorsal and flanks.
Morphology
Periophthalmus argentilineatus is a compact, muscular fish reaching around 4.5 in total length, though most individuals are found in the 3–4 in range. The body is cylindrical and robust, tapering to a rounded caudal fin, and the head is notably large relative to body length, with mobile, protruding eyes set high on the skull — the eyes can be retracted into moistened sockets to keep them from drying out on land, and can swivel independently to scan for predators and rivals.
The colouration is a pale brownish-grey to olive dorsally, grading to whitish below, marked with dark bars, blotches and fine spots across the flanks and dorsal surface that provide camouflage against the mottled mud and root surfaces of the mangrove floor. The first dorsal fin is tall, erectile, and conspicuously marked, and is raised during territorial and courtship displays. As a true goby, the pelvic fins are fused into the characteristic cup-shaped sucker disc that enables the fish to cling to surfaces and prop itself upright during terrestrial movement.
Sexual dimorphism is modest. Males typically grow larger, have taller and more elaborately developed dorsal fins, and show more vivid colouration and fin displays during breeding season. Females are somewhat smaller and plainer, and can be identified by a fuller abdomen when gravid.
Habitat
This is a species of tropical intertidal and estuarine environments. Periophthalmus argentilineatus occupies the brackish, muddy interface between land and sea — mangrove swamps, tidal mudflats, estuarine creek edges, and the exposed roots and pneumatophores of mangrove forests across the Indo-West Pacific, with records from Indonesia, Malaysia, Thailand, the Philippines, Vietnam, Brunei, and surrounding regions.
The fish is emphatically amphibious. It spends low-tide periods hauled out on exposed mud, breathing air held in enlarged, moist gill chambers and moving across the surface by a distinctive crutching motion using its stiffened pectoral fins. The territory of an individual centres on a self-dug burrow in the soft mud, which serves as a refuge from predators, a breeding site, and a retreat during high water. Temperatures across the range are tropical, typically 72–82 °F; salinity is brackish to near-marine, and the fish tolerates wide fluctuations as the tide cycles.
This is not a freshwater fish and not a typical estuarine fish in the conventional sense. Its primary living space is the air above the mud — the water is the habitat it returns to, not the one it inhabits.
Feeding
Periophthalmus argentilineatus is a micro-predator hunting on land as much as in the water. The natural diet consists of small crustaceans, worms, amphipods, copepods, insect larvae, and other small invertebrates encountered on the mud surface and in the upper layer of sediment. The fish hunts by sight, detecting movement on the mudflat and pursuing prey with quick dashes across the surface.
In a paludarium setting the barred mudskipper should be offered live and frozen meaty foods: bloodworm, brine shrimp, daphnia, small earthworms, and similar items, ideally placed on the land area where the fish can hunt them in a naturalistic way. It is not an algae grazer, not a scavenger, and is very unlikely to accept dry flake or pellet foods. A diet of varied, appropriately sized live and frozen invertebrates is essential for long-term health and condition.
Mating
Breeding in mudskippers is one of the most extraordinary reproductive strategies among gobies. Males establish and defend individual burrow territories on the mudflat, and during the breeding season these territories become highly contested. Rival males face off with raised dorsal fins, flaring opercular flaps, and vigorous chasing, and the outcome determines access to prime spawning burrows.
A male courts a visiting female by displaying from the burrow entrance — raising the tall first dorsal fin, performing leaping and fin-spread displays, and leading the female toward the burrow mouth. The quality and depth of the burrow, and the male's ability to maintain an air pocket inside it, appear to be key signals to the female. Courtship can be prolonged and energetically demanding for both sexes.
Breeding
Spawning in Periophthalmus argentilineatus occurs inside the male's burrow, which is a J- or Y-shaped tunnel dug into the soft mud of the intertidal zone. The key feature is that the male creates and maintains an air-filled chamber at the deepest part of the burrow, topping it up by mouthfuls of air carried from the surface. It is into this air pocket that the female deposits her adhesive eggs, attaching them to the burrow wall above the waterline. The male then remains inside, guarding the eggs and replenishing the air supply — a form of parental care unique among fishes in its dependence on a self-constructed atmospheric chamber.
After hatching, the larvae are pelagic and disperse into open brackish or marine water for their larval development. This combination — a highly specialised terrestrial spawning site plus pelagic larvae that require estuarine or marine conditions — means that the barred mudskipper has never been reliably bred in home aquaria. Captive breeding would require replicating precise mud architecture, tidal cycling, controlled atmospheric humidity, and appropriate larval-rearing conditions that no hobbyist has yet managed at scale. Aquarium specimens are effectively always wild-collected.
In the aquarium
The barred mudskipper is a specialist's fish and demands a setup completely unlike a conventional aquarium. The correct enclosure is a PALUDARIUM: a covered, humidity-retaining vivarium with a substantial land area — sand or fine mud substrate with roots, cork bark, or stones to climb — and a shallow brackish-water section for the fish to return to. Humidity inside the enclosure should be kept above 80%; without it, the fish's exposed skin and gill chambers dry out rapidly. Stagnant air is harmful — ventilation is needed, but not at the cost of humidity.
Salinity in the water section should be light brackish (around 2–5 ppt specific gravity), mimicking the estuarine conditions of the species' natural habitat. Temperature should be maintained in the tropical range, 75–82 °F. Males are strongly territorial and aggressive toward one another; a single specimen, a single pair, or a pairing with ample territory are the realistic options. A secure lid is absolutely essential — mudskippers are capable, determined escapees.
Feeding must happen on the land portion. The fish should be offered live or frozen invertebrates placed on the land surface where it can hunt them naturally; drop-fed items into the water are often ignored. Longevity in good conditions reaches 4–6 years. This is not a community fish and not a beginner's fish; it is a compelling behavioural subject for aquarists willing to build and maintain a specialised paludarium.
Conservation
Periophthalmus argentilineatus is assessed as Least Concern on the IUCN Red List (2020 assessment), reflecting its wide distribution across Indo-West Pacific mangrove and estuarine systems and the absence of evidence for major population-level threats. The species is common throughout its range and its population trend is considered stable.
The broader conservation concern for this and all mudskippers is the fate of intertidal mangrove habitat. Mangrove forests and estuarine mudflats continue to be cleared and converted across Southeast Asia for aquaculture, coastal development, and urban expansion — a pressure that directly removes the intertidal breeding and foraging habitat on which mudskippers depend. The barred mudskipper is widespread and abundant enough to absorb this pressure at the species level for now, but local populations in heavily developed coastlines are likely reduced. Because captive breeding is essentially impractical, any trade in the species is supported entirely by wild collection — a consideration for the rare hobbyist who takes on this demanding fish.