Taxonomy & naming
Macrognathus orthosemos was described by Britz and Kottelat in 2020. The type locality is Chaung Gyi stream, a tributary of Khamaungthawe stream near upper Seikphyone village, Tenasserim drainage, at about 722 ft elevation. The Catalog of Fishes (Eschmeyer, CAS) is the authority for the valid name. The family is Mastacembelidae, the spiny eels.
Morphology
Macrognathus are slender, elongate eels with a soft, fleshy snout and a row of short spines before the dorsal fin. Size and the colour pattern that distinguishes this species are given in the original description, which the atlas has not compiled.
Habitat
A small hill stream at about 722 ft in southern Myanmar. Spiny eels generally hide in sand, gravel and leaf litter by day, and no habitat detail specific to this species has been published.
Feeding
Macrognathus are nocturnal predators of small invertebrates; this is a genus-level statement.
Mating
Courtship has not been described for this species.
Breeding
Spawning has not been described, in the wild or in captivity.
In the aquarium
Husbandry has not been documented for this species. Spiny eels in general need a fine sand floor to burrow in, secure lids, and gentle company, and they often feed best at night.
Conservation
Macrognathus orthosemos has not been assessed by the IUCN. It is known only from the Tenasserim drainage of Myanmar, so it should be treated as a locally restricted fish with an undocumented status. Wild-collected animals in the trade should be viewed with that in mind.