Taxonomy & naming
Macrognathus pavo was described in 2010 by Ralf Britz in the journal Ichthyological Exploration of Freshwaters, as one of four new Macrognathus species documented from Myanmar in the same publication. The Catalog of Fishes (Eschmeyer, the authority for valid names) records the valid combination as Macrognathus pavo Britz, 2010. The genus Macrognathus belongs to the family Mastacembelidae, within the order Synbranchiformes — the same order as the swamp eels (Synbranchidae). This placement is the essential fact about the fish: it is a spiny eel, not a true eel. The true eels belong to the entirely unrelated order Anguilliformes, and the elongate body of spiny eels is a convergent adaptation to a burrowing, benthic lifestyle rather than evidence of shared ancestry.
Macrognathus pavo belongs to what researchers working on Myanmar spiny eels refer to as the Macrognathus aculeatus species group. Within this complex it is distinguished primarily by its unusually low dorsal spine count — only four to six isolated dorsal spines preceding the soft dorsal, fewer than any other known member of the genus — and by having six to eight rostral tooth plates. Comparative morphometric studies have confirmed this diagnostic combination. The species epithet pavo is Latin for 'peacock', though the basis for that comparison is not elaborated in the primary description.
Morphology
Macrognathus pavo is a small spiny eel, reaching at most 6 in standard length in the one measured specimen series reported by FishBase. The body is greatly elongated and laterally compressed toward the tail — the classic mastacembelid profile — and the skin is scaleless to the casual eye, covered instead with tiny embedded scales beneath a layer of mucus. The snout is drawn out into the short fleshy proboscis characteristic of Macrognathus, tipped with paired tubular nostrils.
The defining morphological feature is the remarkably low number of isolated dorsal spines: four to six, compared with the higher counts typical in close relatives. The soft dorsal ray count is 53 to 55 and the anal soft ray count is 47 to 51, with three anal spines. No coloration notes from living specimens are available in the published literature; most morphometric data derive from preserved type material. Compared with congeners its diagnostic value lies in fin-spine reduction and rostral dentition (six to eight rostral tooth plates) rather than colour pattern, which is not well characterised in the description.
Habitat
The only known locality for Macrognathus pavo is the Kyeintali Chaung, a stream draining the Rakhine Yoma mountain range in western Myanmar near the coast of the Bay of Bengal. This is a montane or sub-montane drainage with a seasonal monsoon regime rather than a large lowland river. Spiny eels of the genus Macrognathus are generally demersal freshwater fishes of soft-substrate streams, floodplains and slow reaches, where they burrow into sand, mud and leaf litter and shelter under roots and debris.
No direct water-chemistry data from the Kyeintali Chaung have been published for this species; the cache records the habitat as a tropical freshwater mountain stream, likely with moderate temperatures given the elevation and seasonal monsoon pattern. Like all mastacembelids, Macrognathus pavo is scaleless and therefore sensitive to copper-based medications and degraded water quality, and it is likely intolerant of heavily polluted or organically loaded water. Its single-stream endemism means that detailed habitat characterisation awaits future fieldwork.
Feeding
FishBase assigns Macrognathus pavo a trophic level of 3.2, placing it in the middle of the food web as a predator of small invertebrates. Like other members of the genus and family it is almost certainly a benthic, nocturnally active carnivore that uses its fleshy, probing snout to root out prey from the substrate — insect larvae, small crustaceans, worms and similar small invertebrates are the presumed staples, consistent with the mastacembelid feeding guild broadly.
No direct feeding observations from wild or captive individuals of Macrognathus pavo have been published, and the species has not been documented in the aquarium hobby to a degree that would have produced captive diet records. The 'data sparse' caution applies: the trophic level figure from FishBase is a modelled estimate based on the fish's ecological position, not an observation from stomach-content analysis.
Mating
No courtship or mating observations exist for Macrognathus pavo. As a member of the family Mastacembelidae it belongs to the group of spiny eels that are substrate egg-scatterers, not the catadromous true eels of family Anguillidae and not the bubble-nest-building swamp eels of family Synbranchidae. In the Mastacembelidae generally, a courting pair will entwine and scatter adhesive eggs among aquatic vegetation, submerged roots or leaf litter in fresh water, with no nest construction and no parental care afterward.
Because the species is known only from type-locality collections in a remote mountain stream and has not been kept or bred in captivity, nothing beyond this family-level inference can be stated. Spawning in related Macrognathus species is thought to be cued by the seasonal monsoon rains, with rising water levels and the resulting flooding of riparian vegetation providing the proximate trigger.
Breeding
Macrognathus pavo has not been bred in captivity. Breeding records for this species are entirely absent from the published and hobby literature, and the fish is not known to have been established in the ornamental trade or in research aquaria. This is not surprising given its extreme endemism: it has been collected from a single stream, described from type material only four years before the date of this article, and subsequently appears to have attracted little aquarium or scientific follow-up.
For the family Mastacembelidae broadly, the pattern when captive spawning does occur is adhesive eggs scattered freely among fine plants or roots, hatching in a few days with no parental care, and larvae that require very fine first foods. Monsoon-mimicking water changes — larger volumes of slightly cooler, softer water — are the conventional trigger attempted for the few mastacembelids that have been bred in captivity. Whether Macrognathus pavo would respond similarly cannot be confirmed, and attempting captive breeding would first require obtaining specimens from the wild, a non-trivial undertaking given the species' restricted range.
In the aquarium
Macrognathus pavo is not established in the ornamental aquarium trade, and no hobbyist care records are available. It is unknown whether specimens have ever been exported from Myanmar or entered commercial channels. Any care guidance must therefore be extrapolated from what is known about the genus Macrognathus and the family Mastacembelidae generally.
All mastacembelids share a set of care requirements that would apply here: a soft sand substrate deep enough to permit burrowing, with retreats such as caves, pipes or dense plant roots; a tight-fitting, fully sealed aquarium lid (spiny eels are notorious escape artists that can squeeze through any gap and will leave the water and die); feeding of meaty, invertebrate-based foods at night when the fish are most active; and avoidance of copper-based medications to which scaleless fishes are acutely sensitive. Given the maximum recorded size of under 6.5 in, Macrognathus pavo would be a small aquarium subject by spiny-eel standards, and a well-planted tank of moderate size would potentially be suitable — if specimens were ever available. At present, this is a fish of scientific rather than hobbyist significance.
Conservation
Macrognathus pavo is assessed as Data Deficient (DD) on the IUCN Red List, with an assessment dated 22 March 2010 — the same year as its scientific description. The DD designation reflects the near-total absence of population data rather than an inference of security: the species is known from a single stream locality in the Rakhine Yoma mountain range of western Myanmar, which makes it one of the most geographically restricted mastacembelids on record.
Single-locality endemics are inherently vulnerable: any event affecting the Kyeintali Chaung — watershed deforestation, agricultural runoff, dam construction, or climate-driven hydrological shifts — could threaten the entire known population. Western Myanmar's coastal ranges have experienced land-use change and remain a region of limited conservation oversight. The low fishing vulnerability score assigned by FishBase (10 of 100) partly reflects the fish's small size and low commercial value, but that metric does not address habitat loss. A formal reassessment with field surveys to determine the actual extent of occurrence would be the first step toward a data-informed Red List category.