Abstract
A single specimen of the moray eel identified as Gymnothorax polyuranodon (Bleeker, 1853) recently collected from the freshwater area of a river in Iriomote Island, Yaeyama Islands, is the first record of the species from Japan. The specimen was characterized as follows: total vertebrae 147 (predorsal 10, preanal 72); body with irregular black specks; vertical fins low; jaw teeth in two or three irregular rows; anus posterior to mid-body; preanal length 54.2 % of total length, head length 9.3 %, trunk 44 %; body depth 4.1 at gill opening, 4.9 at mid-anus; predorsal length 83.1 % of head length, upper-jaw length 25.8 %, lower-jaw length 22.7 %, snout length 10.7 %, eye diameter 4.9 %, interorbital width 9.1 %; dorsal-fin height 29.7 % of body depth at anus. A new standard Japanese name “Kokuhan-kawautsubo” is proposed for the species. This seemingly rare occurrence of the species is considered to be natural dispersal; while an established population is unlikely, it is necessary to monitor its occurrence from a conservation perspective, with reference to previous cases of fishes inhabiting similar environments.
