Taxonomy & naming
Macrognathus dorsiocellatus was described by the German ichthyologist Ralf Britz in 2010, making it one of the more recently named members of its genus. The Catalog of Fishes (Eschmeyer, California Academy of Sciences) records it as valid under Macrognathus, a large Asian genus within the family Mastacembelidae. No prior combination under Mastacembelus or any other genus has been found in the literature; the species entered the record directly in Macrognathus and has remained there.
The family Mastacembelidae, the spiny eels, are members of the order Synbranchiformes. This placement is the key taxonomic fact about the group: spiny eels are not true eels, which belong to the entirely separate order Anguilliformes. The eel-like body of Macrognathus dorsiocellatus is convergent — an independently evolved adaptation to burrowing and a benthic way of life — rather than evidence of kinship with Anguilla or its relatives. Within Synbranchiformes, Mastacembelidae is most closely related to the swamp eels (Synbranchidae), not to any marine or catadromous lineage.
The species name dorsiocellatus refers to the row of ocelli (eye-spots) along the dorsal fin: Latin dorsi (of the back) and ocellatus (eye-spotted). The FishBase record shows 7–11 small ocelli along the soft dorsal, a diagnostic character that separates it from several sympatric Macrognathus species.
Morphology
Macrognathus dorsiocellatus reaches a maximum recorded standard length of 10 in, making it a mid-sized member of the genus. The body is elongate, strongly compressed posteriorly, and scaleless to casual inspection — the tiny embedded scales are hidden beneath a layer of mucus that gives the fish a smooth, slippery surface. The snout is extended into a fleshy, mobile proboscis tipped with tubular nostrils, characteristic of Macrognathus and used to probe soft substrate in search of buried prey.
Along the back, ahead of the soft dorsal fin, runs a series of isolated short spines — the "spiny" of spiny eel — that give the family its name and which can be erected as a modest defence. Meristic data from FishBase record 14–22 dorsal spines, 51–61 soft dorsal rays, 3 anal spines, 51–60 anal soft rays, and 72–80 vertebrae; the rostral tooth plates number 19–23. The diagnostic character of the species is the row of 7–11 small ocelli on the soft dorsal fin, visible in well-lit conditions. Sexual dimorphism is not externally prominent; ripe females may appear fuller-bodied than males.
Habitat
The species is native to three river systems in Myanmar: the Ayeyarwaddy (Irrawaddy), lower Sittang, and lower Salween basins. These are major Southeast Asian drainages draining the mountains of northern and central Myanmar to the sea, and Macrognathus dorsiocellatus is a freshwater species confined to this region; it does not occur in saltwater or brackish conditions and is not catadromous.
Like other Macrognathus of the region it is a fish of warm lowland rivers, floodplains and slow-moving tributary streams, where soft sand and mud substrates allow burrowing and submerged roots and leaf litter provide shelter. Related species in comparable habitats occupy a temperature range of roughly 75–82 °F (75–82 °F) and a pH of 6.8–7.8; specific water chemistry data for M. dorsiocellatus have not been widely published, and these related-species figures should be treated as indicative rather than formally confirmed. The fish is scaleless and, like all Mastacembelidae, sensitive to copper and to deteriorating water quality.
Feeding
Macrognathus dorsiocellatus is a nocturnal, benthic predator. As in other Macrognathus species, the fleshy, sensitive snout is used to probe through sand, mud, and organic detritus in search of small invertebrates. Natural prey items include aquatic insect larvae, oligochaete worms, and similar small, soft-bodied benthic animals — food typical for a small spiny eel working the substrate after dark.
In the aquarium, related species readily accept live and frozen invertebrates such as bloodworm, tubifex, brine shrimp, and small earthworms. Like other spiny eels it is a nocturnal feeder and may be reluctant to emerge in full light or with competing, fast-moving fish; feeding after lights-out improves uptake and reduces competition stress.
Mating
Macrognathus dorsiocellatus is a spiny eel and, as such, an egg-scattering spawner that gives no parental care — it is not a true eel and does not undertake any catadromous spawning migration. The reproductive pattern inferred for this species follows the Mastacembelidae norm: a courting pair come together during or after the seasonal rains, entwine among fine plants, roots or leaf litter, and scatter adhesive eggs through the vegetation.
No dedicated study of mating behaviour in this species has been published, and documented captive spawnings are not on record. The spawning trigger in related species is typically linked to the onset of the monsoon or wet season — rising water levels, warming temperatures, and increased rainfall that simulate the natural flooding of lowland river margins. There is no nest, no pair bond beyond spawning, and no guarding of eggs or larvae; both parents disperse after spawning.
Breeding
Breeding in captivity has not been formally documented for Macrognathus dorsiocellatus, and the species is rarely encountered in the aquarium hobby. By analogy with better-known Mastacembelidae, captive spawning would require a mature, well-established tank with a soft sand substrate, dense planting or root tangles among which eggs could be scattered, and a pronounced conditioning period of heavy live feeding followed by a simulated wet-season trigger — large, slightly cooler water changes, gradually raising the temperature, and reduced day length.
Eggs in related spiny eels are small and adhesive, hatching in two to three days at tropical temperatures; the larvae are minute and require infusoria or similarly fine first foods before graduating to newly hatched brine shrimp. No parental care is given at any stage. The practical difficulty of sexing a pair, the species' rarity in trade, and the absence of published husbandry records mean that captive breeding remains essentially undescribed and should not be assumed to follow any other mode.
In the aquarium
Macrognathus dorsiocellatus is seldom available to hobbyists, as it is a recently described species from Myanmar with a limited range and little aquarium trade representation. Any care account must be extrapolated from its genus. As a spiny eel it is a nocturnal, burrowing predator that demands a fine sand substrate deep enough to allow complete burial, along with caves, pipes or tangled roots to shelter in by day. Tank lighting should be subdued, and feeding should take place after dark.
Like all Mastacembelidae, it is scaleless and acutely sensitive to copper-based medications — standard disease treatments that contain copper are dangerous and must not be used. Water quality must be consistently good; the fish is not tolerant of ammonia or nitrite spikes. It is also an escape artist: spiny eels are capable climbers and will exploit any gap in a lid, breathing atmospheric air at the surface before expiring on the floor. A tight-fitting, fully sealed cover is essential. Tank mates should be peaceful and large enough not to be swallowed at night; small invertebrates and tiny fish are potential prey. At a maximum of 10 in this is a manageable aquarium fish in terms of adult size, though it does best in at least 20 US gal of well-maintained, planted water.
Conservation
Macrognathus dorsiocellatus is assessed as Least Concern on the IUCN Red List. Its range encompasses three major Myanmar river systems — the Ayeyarwaddy, Sittang and Salween — which together represent a substantial area of lowland freshwater habitat, and there is no current evidence of a population-level decline that would warrant a higher threat category.
Nonetheless, the lowland rivers of Myanmar face increasing pressure from dam construction, agricultural runoff, sand extraction and habitat modification along floodplain margins. As a narrowly endemic species with a known distribution confined to one country, M. dorsiocellatus is more vulnerable to localised threats than wide-ranging relatives. Its scaleless body and sensitivity to water quality mean that pollution events can be locally significant. The species was described only in 2010, and survey data on population density and trends are limited; sustained monitoring of the Myanmar river basins it inhabits would be needed before its long-term security could be confirmed.