Hemirhamphodon byssus Tan & Lim, 2013

Family:  Zenarchopteridae (Internally fertilized halfbeaks)
Max. size:  7.13 cm SL (male/unsexed)
Environment:  pelagic; freshwater; depth range - 0 m
Distribution:  Asia: southern to central Sarawak (South of Rejang basin) in Malaysia.
Diagnosis:  Distinguished from other species of Hemirahamphodon in having the following characters: dorsal fi n with melanophores in two sizes on both male and female examples above 30 mm SL, interradial membranes on the anterior half of the dorsal fin with large and intense melanophores throughout fi n depth, appearing as thin black streaks. 2) Unique dorsal fi n morphology on large males above 50 mm SL - distal portions of fi rst 6 to 7 rays elongated, free of interradial membrane, projected into fi laments up to four times the depth of the dorsal fi n; adpressed fi n rays reaching half of caudal-fin. 3). Males with an enlarged posterior projection on the fourth anal-fi n ray, with third, fourth and eighth anal-fin rays branched; females with third, fourth and eighth anal-fi n rays branched; pelvic-fin origin anterior to dorsal-fi n origin. 5) Dorsal-fin rays 13 to 14 (Ref. 94086).
Biology:  This species inhabits streams of lowland forest and peat swamps. In streams with clear water, the body is lighter in color while in tannin stained waters, the body tends to be darker colored, at times appearing black (Ref. 94086).
IUCN Red List Status: Least Concern (LC); Date assessed: 16 January 2020 Ref. (130435)
Threat to humans:  harmless

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