Taxonomy & naming
Acentrogobius viridipunctatus was described by Achille Valenciennes in 1837, most probably in the monumental Cuvier & Valenciennes Histoire naturelle des poissons, the pre-eminent fish reference of its era. The original combination was Gobius viridipunctatus, reflecting the nineteenth-century habit of placing virtually all small gobies in Gobius. The species was later transferred to Acentrogobius, a large genus of small Indo-Pacific estuarine gobies, where it currently resides under the Catalog of Fishes (Eschmeyer, CAS), the authority for valid names.
The family placement is Oxudercidae under current Catalog of Fishes taxonomy, which absorbs the former Gobionellidae along with the mudskippers and several other lineages previously held in Gobiidae. All members of Oxudercidae are true gobies in the broad sense: they possess pelvic fins fused into a cup-shaped sucker disc, the synapomorphy that defines the true gobies and sets them apart from the sleeper gobies (Eleotridae), whose pelvic fins remain separate. Gobies as a whole are overwhelmingly marine — the family constitutes one of the largest and most species-rich fish groups in the sea — and Acentrogobius viridipunctatus, despite occasional penetration into fresh water, belongs firmly to that estuarine, salt-influenced end of the spectrum.
Morphology
Acentrogobius viridipunctatus is a small, elongate goby reaching around 1–2 in in standard length. The body is pale greenish or yellowish-tan, scattered with numerous small vivid green or turquoise spots that give the fish both its scientific name (viridipunctatus — green-spotted) and its common name; the fins are transparent to faintly pigmented. The head is broad and slightly depressed, with the large, upward-facing eyes characteristic of a benthic ambush predator, and the mouth is relatively wide and oblique — suited to engulfing small prey.
The defining morphological feature, shared with all true gobies, is the fused pelvic disc: the two pelvic fins are united along the midline, forming a concave sucker that the fish uses to anchor itself to hard substrate in the tidal current. Sexes are difficult to distinguish externally outside of breeding condition; males may develop slightly more intense colouration and fuller finnage when ripe, and females show a rounded abdomen when gravid. Detailed external sexual dimorphism is not strongly marked in this species, and accurate sexing usually requires close examination of the genital papilla.
Habitat
The spotted green goby inhabits brackish estuaries, tidal rivers, mangrove-fringed creeks and the lower reaches of coastal rivers across the Indo-West-Pacific, with records spanning South and Southeast Asia. It is a benthic species, spending most of its time on or very close to the bottom — mud, sand and gravel substrates among the roots and detritus of mangrove and tidal zones — and is typically found in water with measurable salinity, in the range of roughly 5–15 ppt, though it may occasionally wander into fresh water or higher-salinity estuarine zones.
Water parameters in these estuarine habitats are warm (approximately 75–82 °F), with pH generally in the neutral to slightly alkaline range (7.0–8.0) reflecting the marine influence. Tidal fluctuation brings regular changes in salinity, temperature and dissolved oxygen, and the species is adapted to moderate parameter swings. It is emphatically not a fish of soft, acidic blackwater streams; the ion-rich, brackish estuarine environment is central to its physiology and long-term health.
Feeding
Acentrogobius viridipunctatus is a micro-predator. In the wild it forages along the estuary bottom for small invertebrates: copepods, amphipods, small worms, insect larvae and tiny crustaceans picked from the substrate or snatched from the water column above it. The oblique, relatively wide mouth reflects a fish that can take prey of reasonable size relative to its own body.
In the aquarium this species typically shows little interest in dried flake or pellet foods, at least initially, and may refuse them entirely. Success depends on offering small live and frozen foods: bloodworm (chironomid larvae), brine shrimp, daphnia, copepods, cyclops and frozen mysis are all appropriate and will be taken readily. Conditioning a pair for breeding specifically calls for live or high-quality frozen foods fed little and often; fish kept on flake alone tend to lose condition and vigour over time. As with most gobies, the feeding response is sight-triggered, and actively moving prey elicits a far stronger response than static pellets.
Mating
Acentrogobius viridipunctatus is a resident brackish cave-spawner, a breeding strategy shared by many of the small estuarine gobies that do not depend on a marine larval phase. A ripe male selects and defends a suitable hollow — a crevice among rock or mangrove root, a half-buried shell, a length of pipe — and signals his readiness through postural displays and intensified colouration. Rival males are driven off; a receptive female is courted with lateral displays and fin-spreading before she is led to the spawning site.
Unlike the amphidromous gobies (Stiphodon, Sicyopterus and allies) that release tiny hatchlings to drift seaward and develop as marine plankton — and so cannot be captive-bred — resident estuarine spawners like Acentrogobius complete their entire breeding cycle in the same brackish environment. This makes captive breeding at least theoretically feasible provided water quality and salinity are maintained correctly. The pairing is typically brief; once spawning is complete the female's role ends and the male takes sole charge of the clutch.
Breeding
Spawning follows the typical cave-spawning goby pattern: the female deposits a cluster of adhesive, pear-shaped eggs on the roof or wall of the chosen cavity, then departs. The male remains, fanning the eggs with his pectoral fins to ensure oxygenation and clearing away any unfertilised or fungused eggs to protect the clutch. Depending on temperature, hatching takes approximately five to ten days.
The newly hatched larvae are very small and require appropriately tiny first foods — infusoria, rotifers or commercial fry food of suitable particle size — before graduating to newly hatched brine shrimp nauplii as they grow. Because the whole cycle takes place in brackish water, a separate rearing tank should also be maintained at an appropriate salinity; placing fry into plain fresh water will cause osmotic stress. Captive breeding records for this species specifically are sparse in the hobby literature, but the biology is consistent with successful reproduction in a well-set-up brackish aquarium.
In the aquarium
The spotted green goby is an occasional import rather than a staple of the hobby, and its care demands are specific enough that it is best described as a species for the dedicated brackish-tank keeper. The single non-negotiable requirement is genuinely brackish water: a specific gravity of around 1.005–1.010 (roughly 7–14 ppt salinity) should be maintained consistently. Fish kept in plain fresh water may survive for weeks but will gradually lose condition, show dull colouration and become susceptible to disease. A hydrometer or refractometer is essential equipment.
A small tank (10–15 US gal) is sufficient for a pair or small group, with a fine sand substrate, flat stones and dense cover in the form of caves, ceramic pipes, coconut shells or PVC fittings to provide spawning sites and territorial dividers — males will spar with each other if sight lines are unbroken. The tank must be covered: gobies are accomplished jumpers, and an uncovered tank will eventually result in a dry fish on the floor. Filtration should be efficient but flow moderate; these are estuary fish rather than fast-current dwellers. Diet must lean heavily on live and frozen foods. Tankmates, if used, should be other small brackish-tolerant species; avoid soft-water community fish, which will not tolerate the salinity, and large or aggressive fish that will outcompete this small goby for food.
Conservation
Acentrogobius viridipunctatus has not been formally evaluated by the IUCN Red List — it carries no conservation category here, and we record it as Not Evaluated rather than guess at a status. Many small estuarine gobies of South and Southeast Asia fall into this gap simply because survey data are too limited to support a formal assessment, not because the species is necessarily secure.
As a broadly distributed estuarine fish of the Indo-West-Pacific, it likely faces the same pressures that affect coastal and mangrove habitats across the region: mangrove clearance for aquaculture and coastal development, estuarine sedimentation from deforestation catchments, pollution from agriculture and industry, and the general degradation of tidal wetlands. Whether the species is widespread enough to be buffered against these pressures, or whether any populations are locally restricted, is not established in the published record. Trade volume in the hobby is low and the species does not appear to be targeted commercially, so there is no evidence of trade-related pressure on wild populations.