Taxonomy & naming
Pseudogobiopsis tigrellus was originally described by the American ichthyologist John Treadwell Nichols in 1951 in the American Museum Novitates (No. 1539), in a paper titled 'Four new gobies from New Guinea.' The holotype (AMNH 18574) was collected at Bernhard Camp on the Idenburg River, elevation 246 ft, in the upper Mamberamo drainage of what is now the Indonesian province of West Papua, along with nine paratypes (AMNH 15096). The species was placed by Nichols in the large catch-all genus Gobius; subsequent revision moved it to Pseudogobiopsis, where the Catalog of Fishes (Eschmeyer, CAS) — the authority for valid names — recognises it today.
The genus Pseudogobiopsis belongs to the family Oxudercidae, subfamily Gobionellinae, within the broader assemblage of true gobies. True gobies are defined by the fusion of the pelvic fins into a cup-shaped sucker disc — a character that unites this genus with the rest of the Gobioidei that are placed in Oxudercidae, and that sets all true gobies apart from the sleepers and gudgeons (Eleotridae), whose pelvic fins remain separate. Gobies as a group are overwhelmingly marine; freshwater representatives such as P. tigrellus are the exception rather than the rule.
The species epithet tigrellus is a Latinised diminutive suggesting a small tiger-like animal, presumably alluding to a striped or banded pattern on the tiny body, though the type description is the principal source of morphological detail. No synonyms are recorded.
Morphology
Pseudogobiopsis tigrellus is an extremely small goby: the type series yields a maximum standard length of 1 in in males, making it among the smallest gobies in New Guinea. The ResearchGate figure of the type-series specimen (WAM P.31752-001, 1 in SL male, Mamberamo River) confirms this diminutive size. As a true goby it possesses fused pelvic fins forming a cup-shaped adhesive disc on the ventral surface — the hallmark of the family and the key character distinguishing it from superficially similar eleotrid gudgeons of the region.
Beyond size and the diagnostic pelvic disc, detailed morphological data remain sparse. The name tigrellus suggests a striped or banded patterning, consistent with the coloration of related Pseudogobiopsis species in which faint bars or transverse markings are visible on the flanks of preserved specimens. No live-colour photographs are publicly available. Sexual dimorphism, if present at this scale, has not been formally described.
Habitat
All known collection records place Pseudogobiopsis tigrellus within the Mamberamo River system of West Papua, Indonesia — one of the largest and most biologically intact river systems in the Asia-Pacific region, draining the interior of the Vogelkop–Bird's Head peninsula and the surrounding mountains. The type specimens were taken at an elevation of 246 ft at Bernhard Camp on the Idenburg River, a major tributary of the Mamberamo.
FishBase records a very specific microhabitat: shallow pools approximately 4 in in depth over sand and rocky substrate, in fresh water. The fish was noted as demersal — living and foraging on or near the bottom — and was found solitary or in loose groups of two to four individuals. This suggests a habitat of quiet, shallow, clear lowland or foothill stream margins or backwater pools rather than fast-flowing mainstream channels. No water temperature, pH, or conductivity data are available for the collection site.
Feeding
No direct feeding observations exist for Pseudogobiopsis tigrellus in the wild. By analogy with related small resident gobies of the Gobionellinae, it is almost certainly a micro-predator, taking small benthic invertebrates — tiny crustaceans, insect larvae and aquatic worms — from the sand and rock substrate of the shallow pools in which it lives. True gobies of this body size typically hunt by sight, picking at prey items on or near the bottom rather than filtering water or grazing algae.
Because no aquarium-kept specimens are recorded, nothing is known about food acceptance in captivity. If the fish were ever maintained, the starting point for any micro-predator of this size would be small live and frozen foods — copepods, newly hatched brine shrimp, bloodworm (chopped), and similar items — sized appropriately for a mouth no wider than the head of a fish barely 1 in long. Acceptance of dry foods would be unpredictable.
Mating
No mating or courtship behaviour has been observed or described for Pseudogobiopsis tigrellus. The genus Pseudogobiopsis belongs to the Gobionellinae, a subfamily whose members are predominantly resident freshwater or brackish-water gobies — not amphidromous species that require a marine larval phase. On that basis, and by comparison with other small Gobionellinae such as Rhinogobius and Stigmatogobius, the species is expected to be a resident cave or substrate spawner in which the male guards a clutch of adhesive eggs.
In the absence of any recorded observations, caution is warranted. The brevity of the species' known occurrence — a single collecting event at a single locality — means that virtually nothing about its reproductive biology can be stated with certainty. What can be said is that no amphidromous behaviour has been proposed or suggested in the literature for any Pseudogobiopsis species.
Breeding
No breeding records exist for Pseudogobiopsis tigrellus either in the wild or in captivity. On the basis of the genus-level biology and the subfamily pattern, the most plausible reproductive mode is that of a resident substrate spawner: a male defends a small cavity, crevice or area of hard substrate; the female deposits adhesive eggs; and the male guards and fans them until hatching. This pattern — repeated across many small Gobionellinae — allows the entire life cycle to be completed in fresh or lightly brackish water without a marine dispersal phase.
Because the species is essentially unknown to aquarists and has not been collected in modern times, captive breeding has never been reported. Any future attempt would face the primary challenge of acquiring legally exported, properly identified wild material — a significant obstacle given the remoteness of the Mamberamo drainage and the rarity of the species in collections.
In the aquarium
Pseudogobiopsis tigrellus is not an aquarium fish in any practical sense. It has never been kept in captivity, is known from only ten museum specimens, and its range lies deep within the Mamberamo River drainage of West Papua — a region that is both difficult to access and whose freshwater fauna is subject to Indonesian export restrictions. No commercial collection or import has been recorded.
Were it ever to become available, its extreme small size (maximum 1 in SL) would make it a nano-aquarium subject at most, requiring a small, quiet, well-filtered tank with a sand or fine-gravel substrate, gentle flow, and a diet of the smallest live and frozen invertebrate foods. Males of small substrate-spawning gobies are territorial and would need hiding places and line-of-sight breaks. Given the absence of any husbandry data, prospective keepers would be working entirely in the dark. The fish is best appreciated as a scientific curiosity representative of New Guinea's exceptional freshwater biodiversity rather than a realistic aquarium candidate.
Conservation
The IUCN Red List assessed Pseudogobiopsis tigrellus as Data Deficient (DD) in February 2020. This reflects what the available evidence actually shows: the species is known from a single collection of ten specimens taken in 1939, and no confirmed recollection from the Mamberamo system has been published since. It is unclear whether the species is genuinely rare, localised to a narrow microhabitat that has not been resurveyed, or simply overlooked during the limited ichthyological surveys the remote interior of West Papua has received.
The Mamberamo drainage is one of the most ecologically intact large river systems remaining in the Asia-Pacific region, buffered by the difficulty of access and relatively low human population density in its upper reaches. Nevertheless, deforestation, mining concessions and infrastructure development are advancing into the region, and the shallow-pool microhabitat this species occupies could be sensitive to sedimentation and flow alteration. The priority for conservation is survey work: targeted aquatic biodiversity assessment of the Idenburg River and surrounding drainages to determine whether the species persists, what its current range is, and whether a more informative IUCN category can be assigned.