Taxonomy & naming
Bleeker described the species in 1854 as Muraena polyuranodon from Ceram, in the Moluccas. It is a true moray in the family Muraenidae, and the vernacular name freshwater moray refers to its tolerance of low salinity, not to a separate lineage. Trade names for it include freshwater moray eel.
Morphology
A long, scaleless, laterally flattened eel with a single continuous fin along back, tail and belly and no pectoral or pelvic fins. FishBase gives a maximum length of 59 in TL.
Habitat
FishBase records it from lentic and lotic freshwater and from estuarine and marine habitats. It usually lives within 12–19 mi of the sea and up to about 98–131 ft elevation. The range runs from Sri Lanka through Indonesia, Borneo, New Guinea and the Philippines to Fiji, with reports from Palau, Australia, New Caledonia and Vanuatu.
Feeding
Morays are predators. Wild diet is not detailed in FishBase for this species; in captivity it takes whole fish, shrimp and chopped fish or squid.
Mating
Courtship and spawning have not been described for this species.
Breeding
Reproduction is not documented in captivity. Morays are generally understood to spawn in open water with pelagic larvae, and no aquarium breeding of this species is recorded.
In the aquarium
A large, predatory, long-lived fish that needs a big tank with a tight lid and plenty of tubes and caves. Keep it with fish too large to swallow, and expect it to eat anything that fits in its mouth. Many dealers keep it in low-salinity or brackish water, and it is often held in fresh water for long periods. FishBase gives no water chemistry range.
Conservation
The IUCN assessed Gymnothorax polyuranodon as Least Concern in 2019, reflecting its wide Indo-Pacific range.