Taxonomy & naming
Macrognathus morehensis was described by L. Arunkumar and H. Tombi Singh in 2000 from a holotype of 6 in total length collected at Maklang, Manipur, in northeastern India. The Catalog of Fishes (Eschmeyer, the authority for valid names) records it in the genus Macrognathus Lacepède, the Asian spiny-eel genus of the family Mastacembelidae within the order Synbranchiformes. Mastacembelidae are the spiny eels, so called for the row of isolated short spines ahead of the soft dorsal fin; they are kin to the swamp eels rather than to the true eels, and their elongate, scaleless body is a convergent form, not evidence of close relationship to the Anguilliformes.
The genus Macrognathus is the principal Asian spiny-eel genus, spanning India, Indochina, Sundaland and parts of southern China. It is distinguished from its close relative Mastacembelus in part by characters of the rostral region and the number of dorsal spines. Macrognathus morehensis has no formally recognised common name in the aquarium trade; the species epithet references Moreh, the town near Maklang on the India–Myanmar border in Manipur, reflecting the type-locality geography.
Morphology
The only specimen on record for this species is the holotype at 6 in total length, giving a maximum known size of approximately 6 in, though the true adult size of the species in the wild remains unknown from so limited a sample. Like all Macrognathus, it would have the characteristic spiny-eel body plan: greatly elongate and laterally compressed posteriorly, with a rostral proboscis — the fleshy, tubular snout used to probe the substrate — tubular nostrils, and a series of isolated dorsal spines running ahead of the soft rayed dorsal fin, which joins the caudal and anal fins in a continuous fringe around the tail.
The skin lacks visible scales and is covered in mucus, a feature shared by all Mastacembelidae. Detailed colour pattern notes and fin-ray counts for the species can be found in the original description by Arunkumar and Tombi Singh. Given how little material is available, comparisons with similar northeast Indian Macrognathus species require caution.
Habitat
Macrognathus morehensis is known from the freshwaters of Manipur, a hilly state of northeastern India situated at the head of the Indo-Burma biodiversity hotspot. The rivers of Manipur drain toward Myanmar and eventually the Chindwin-Irrawaddy basin, placing this species in the greater Irrawaddy drainage of tropical southern Asia. Based on what is known from FishBase, the species is demersal and tropical in habit, consistent with the guild of bottom-dwelling, warm-water spiny eels.
As with other Mastacembelidae, Macrognathus morehensis is presumed to favour soft-bottomed substrates — sandy or muddy streambeds and the margins of lowland rivers, floodplain streams and pools — where it can burrow and conceal itself during the day. Vegetation and submerged root tangles likely serve as additional shelter. Precise water-chemistry parameters have not been recorded for the type locality, but the rivers of Manipur are generally soft to moderately hard, warm freshwaters typical of lowland tropical streams at low to mid elevation.
Feeding
Spiny eels of the family Mastacembelidae, including Macrognathus, are nocturnal benthic predators. The fleshy, probing snout is adapted to root out invertebrates from sediment and leaf litter — insect larvae, worms, small crustaceans and other benthic invertebrates form the core diet in the wild. FishBase records a trophic level of 3.3 ± 0.4 for this species, consistent with a secondary carnivore feeding primarily on invertebrates rather than fish.
No specific feeding observations exist for Macrognathus morehensis in the wild or in captivity. In line with the wider Macrognathus genus, it would be expected to hunt after dark along the substrate, using chemosensory and tactile cues rather than vision as the primary hunting tools.
Mating
No mating observations have been recorded for Macrognathus morehensis. The reproductive biology of the species is entirely undescribed. Based on the biology of Mastacembelidae generally, mating is expected to involve a pair that courts and spawns among aquatic vegetation, roots or leaf litter in fresh water, with no nest construction and no lasting pair bond. In related species, spawning appears to be triggered by seasonal cues — rising water temperatures and increased rainfall associated with the monsoon are the likely proximate triggers in the rivers of Manipur.
This species is not a true eel and does not undertake any sea-going reproductive migration; it is a freshwater resident that breeds in the river systems of its native range.
Breeding
Macrognathus morehensis has never been bred in an aquarium, and based on the broader biology of Mastacembelidae it is a substrate egg-scatterer. A courting pair scatters small, adhesive eggs among fine plants, roots or leaf litter in fresh water; no parental care is provided and the adults do not guard the eggs or larvae. In the few documented captive spawnings of related Macrognathus species, eggs are clear and adhesive, around 0.5 in in diameter, and hatch in approximately three days at tropical temperatures, producing tiny larvae that initially require infusoria-grade foods before graduating to newly hatched brine shrimp.
Given the obscurity of the species in science and its complete absence from the aquarium trade, captive breeding of Macrognathus morehensis is unlikely to have occurred. The species is known from a single holotype specimen, so even its adult reproductive condition has not been described.
In the aquarium
Macrognathus morehensis is not kept in the aquarium hobby and is unknown in commercial trade. It was described from a single wild specimen and has not been collected again in sufficient numbers to enter the ornamental fish market. Were it to become available, the requirements of the genus Macrognathus would apply: a soft sand substrate deep enough to burrow into, caves and shaded retreats, warm tropical water, and a fully sealed aquarium lid — spiny eels are skilled escape artists that can climb surprisingly well and will leave an uncovered tank.
All Mastacembelidae are scaleless and particularly sensitive to copper-based medications and to poor water quality. Suitable tankmates would be robust, peaceful species too large to be swallowed, avoiding small tetras or other fish that a nocturnal predator might take at night. Meaty foods offered in the evening — bloodworms, earthworm pieces, sinking carnivore pellets — would be appropriate.
The small size implied by the holotype (around 6 in) would make Macrognathus morehensis one of the smaller members of the genus and potentially more suitable for a modest-sized setup than the large flagship spiny eels — but this remains speculative from so little material.
Conservation
Macrognathus morehensis is assessed as Least Concern on the IUCN Red List (assessed January 2010). The assessment does not imply that the species is well known or widespread; rather, at the time of evaluation the available data did not meet the quantitative criteria for a threatened category.
In practice, the species is known from a single holotype collected at one locality in Manipur, and there is no information on its population size, distribution, or trends. The rivers of northeastern India sit within the Indo-Burma biodiversity hotspot, one of the world's most threatened and least surveyed regions for freshwater fish. Pressures in this region include deforestation, agricultural runoff, sand mining, and the damming of rivers for hydropower projects that are expanding rapidly across the Chindwin-Irrawaddy drainage. Any narrowly endemic species in a single river system in Manipur faces genuine long-term risk. The Least Concern assessment should be read in the context of extreme data scarcity rather than confirmed population stability.