Amblyrhynchichthys micracanthus

Ng & Kottelat, 2004

Order: Cypriniformes
Family: Cyprinidae

Environment: Benthopelagic; freshwater
Climate: Tropical

Description. D iv, 9;  A iii, 5;  P i, 14; V i, 8;  C  i, 9, 8, i.  Lateral line scales 32+2, predorsal scales 11, scales in transverse lines ½5/1/3½, circumpeduncular scales ½3/1/3½, gill rakers on first arch 34-37, vertebrae 20+12=32 or 20+13=33. Body moderately deep and strongly compressed, with narrow predorsal midline. Predorsal profile smoothly rounded with small concavity at nape and then sloping gently ventrally from origin of dorsal fin to end of caudal peduncle. Ventral  profile less convex than dorsal profile, sloping gently ventrally to anterior end of anal fin base, then sloping more steeply dorsally from there to end of caudal peduncle. Lateral line complete. Scales with strongly convergant radii. Head narrow, stout extremely blunt, with a vertical lateral profile. Nostril large and anterioly situated. Barbels none. Eye in upper half of head, visible from dorsal and ventral aspects; moderately large. Hyaline eyelid well developed, covering anterior and posterior quartes of orbit. Suborbital bones fairly large, narrowest directly below eye. Mouth subterminal, with well-devloped groove separating lips from both upper and lover jaws. Lips thick; lower lip present medially and with complete post-labial groove. Gill membranes broadly jointed to isthmus. Gill rakers long, one third as long as opposing  filaments on epibranchial and half as long as opposing filaments on ceratobranchial. Pharyngeal bones stout, with three rows (2,3,4-4,3,2) of curved, chisel-shaped teeth. Grinding surfaces of distal most major teeth widest, width progressively decreasing proximally. Dorsal fin moderately high, with concave distal margin, sharply pointed at apex; origin slightly anterior to pelvic fin origin. Last unbranched ray longest; spinous part with 11 to 18 serrations on posterior edge. Pectoral fin long and falcate, extending to scale row at pelvic fin origin: distal margin concave near tip but straight otherwise. Pelvic fin moderately falcate, extending to slightly more than midway between pelvic fin origin and anterior base anal fin: distal margin nearly straight. Anal fin with strongly concave distal margin and last three posterior rays equal in length; when adpressed against body, extending to middle of caudal peduncle. Two scale rows between urogenital opening and anal fin origin. Caudal peduncle strongly compressed and moderately long. Caudal fin deeply forked, upper and lower lobes pointed. Sexual dimorphism absent. Breeding tubercles absent and body depth between sexes not different. Colour (preserved); body pale brown and a faint broad stripe consisting of aggregations of melanophores on sides of body immediately above lateral line. Dorsal and caudal fins hyaline, with a faint black posterior margin. All other fins hyaline. Colour in life an overall silvery white.  Maximum total length  24 cm.  Maximum standard length  19.7 cm.

It can be distinguished from its only congener, A. truncatus, in having a more truncate snout (with a straight vs. gently rounded lateral profile), shorter dorsal spine (15.5-25.7 %SL vs. 26.7-29.9), smaller eye when similar-sized  individuals of larger than ca. 70 mm SL are compared (28.7-34.9 %HL vs.32.7-36.3), and fewer gill rakers (34-37 vs. 39-40).

Distribution. Lower and middle Mekong, Chao Phraya, Mae Khlong and Tapi River drainages in Indochina (mainland Southeast Asia). In the Mekong, it reaches upriver to Vientiane. Native to Thailand, Cambodia, Laos and Vietnam.

Ecology. Inhabits mainly rivers, with juveniles occasionally entering swamps and flooded fields (Taki, 1978). In the Mekong River drainage, this species moves into the inundated forest during the flood season (June – September) and return to the river in October and Nevember (Rainboth, 1996). It feeds mainly on periphyton: other minor food items include phytoplankton, benthic algae and zooplankton (Rainboth, 1996).