Psilorhynchus tysoni Conway & Pinion, 2016

Family:  Psilorhynchidae (Mountain carps)
Max. size:  5.38 cm SL (male/unsexed)
Environment:  benthopelagic; freshwater,
Distribution:  Asia: known currently only from a few localities on the Mae Nam Moei and its tributary the Hue Mae Song, Tak Province, Thailand (Ref. 110241).
Diagnosis:  Dorsal soft rays (total): -12; Anal soft rays: -8; Vertebrae: -34. Diagnosis: 6–7 dorsal saddles along dorsal midline, including 1-2 between occiput and dorsal-fin origin and 5-6 from dorsal-fin origin to caudal-fin origin; posteriormost dorsal saddle at caudal-fin origin small but prominent and represented by black or dark brown spot; L+1 and L-1 rows restricted to center of body side, not extending posterior to vertical through anal-fin origin; L+2 row absent; dorsal-fin with poorly developed dark brown or black markings along anterior margin; 2 widely separate dark brown or black markings on both upper and lower caudal fin lobes; anguloarticular portion of preoperculo-mandibular canal present; principal caudal-fin rays 10+9; total vertebrae 34 (17+17); body shallow (14–18% SL); caudal peduncle short (11–14% SL); snout short (35–43% HL); mouth narrow (mouth width 21-26% HL) (Ref. 110241). Description: Dorsal profile arched, rising moderately to dorsal-fin origin, sloping gently towards caudal peduncle; body depth greatest at dorsal-fin origin, narrowest at base of caudal peduncle; ventral profile moderately straight from lower jaw to anal-fin origin, weakly concave from anal-fin origin to caudal-fin base; head and eye large, pupil weakly elliptical with longest axis of ellipse orientated along dorsal-ventral body axis; mouth wide; snout moderately long, less than half of head length, rounded anteriorly, its ventral surface bordered by a deep longitudinal groove on each side; rostral cap and upper lip separated by a shallow groove; posterolateralmost part of rostral cap continuous around corner of mouth, contacting skin fold at posterolateral corner of mouth; lower lip portion of lower-jaw cushion broadly rectangular, anterior edge weakly rounded; superficial layer of lower-jaw cushion covered in large, globular papillae; skin fold around posterolateral corner of mouth large and flap-like, continuous anteriorly with posterolateralmost part of upper lip and rostral cap; outer edge of skin fold weakly papilliated with small globular papillae; tubercles absent from surface of skin fold; gill membranes joined to isthmus; pre-epiphyseal and post-epiphyseal fontanelle long and rectangular, separated by a narrow strut of frontal, situated dorsal to the epiphyseal bar; 5 infraorbitals (IO1–5); IO1–3 plate like, IO1 largest of the series; IO4–5 narrow tube-like bones, composed of lateral line canal ossification only; cephalic lateral line canal system well developed; 2 openings in anguloarticular portion of preoperculo-mandibular canal; 6 openings in preopercular portion of preoperculo-mandibular canal; 3 openings in nasal portion of supraorbital canal; parietal portion of supraorbital canal open; 2 openings in parietal portion of temporal canal; 5th ceratobranchial with 1 row of 4 needle-like teeth; no gill-raker ossifications; hyoid bar with 3 branchiostegal rays of similar length and shape; basihyal elongate, rod-shaped; anterior swimbladder chamber surrounded by a thick peritoneal tunic, partially enclosed in a bony capsule formed anteriorly by lateral process of 2nd vertebra and laterally by outer arm of os suspensorium; dorsal-fin rays iii-9; anal-fin rays ii-6; principal caudal-fin rays 10+9, dorsal procurrent rays 8, ventral procurrent rays 5; pectoral fin rays (v-vi)-(11-13), pelvic fin rays ii-(7-8); paired fins horizontally placed, pectoral fins larger than pelvic fins; pectoral fin not reaching vertical through dorsal-fin origin, reaching 2-3 scale rows anterior to pelvic-fin origin when adpressed; pelvic fin insertion opposite 2nd or 3rd branched dorsal-fin ray; well-developed unculiferous paired-fin pads present along ventral surface of 5-6 anteriormost pectoral-fin rays and 2 anteriormost pelvic-fin rays; dorsal fin high, triangular in shape with weakly pointed tip; posterior fin margin weakly concave; anal fin small, triangular in shape with weakly pointed tip, not reaching caudal-fin base when adpressed, posterior fin margin weakly concave; caudal fin moderately forked, tips of upper and lower lobes weakly rounded; scales cycloid, large, with 6–8 well-developed radii over posterior field of scale body; 34-35 scales along lateral line, plus 1-2 on base of caudal fin; 3.5/1/2 transverse scale rows from dorsal-fin origin to pelvic-fin origin, 10-12 predorsal scale rows, 9 scale rows between anus and anal-fin origin; ventral surface between paired fins without scales; 17+17 abdominal and caudal vertebrae (Ref. 110241). Coloration: In alcohol: Body background colour light cream; occiput light to dark brown; dorsal surface between occiput and dorsal fin with 1-2 indistinct dark brown saddles; if 1, saddle situated anterior to midpoint between occiput and dorsal-fin origin, if 2, 2nd saddle located between saddle situated anterior to midpoint between occiput and dorsal-fin origin and dorsal-fin origin; well-developed dark brown saddle at origin of dorsal fin; 4-5 dark brown saddles posterior to dorsal-fin origin; if 4, 1st situated below middle of dorsal fin, 2nd situated midway between posteriormost point of dorsal fin and vertical through anal-fin origin, 3rd situated above posteriormost point of anal fin and 4th (posteriormost saddle) situated at base of caudal fin; if 5, additional saddle located between saddles homologous to 1st and 2nd saddles in specimens with 4; posteriormost saddle reduced to a small but prominent dark brown to black spot; dorsal saddles, excluding 2-3 posterior to saddle located at dorsal-fin origin, without contact to lateral blotches, extending ventrally 1-2 scale rows on body side; 2-3 dorsal saddles posterior to saddle located at dorsal-fin origin extending ventrally 2-3 scale rows on body side and in direct contact with lateral blotches; flank with 6-8 dark brown lateral blotches arranged in a longitudinal row; 1st lateral blotch situated on flank at midpoint between opercular opening and vertical through dorsal-fin origin, and last lateral blotch situated at caudal-fin base; size and position of other lateral blotches along flank highly variable; lateral stripe distinct in largest specimens only; indistinct in smaller individuals scales situated over dorsal surface of body bordered posteriorly with dark brown pigment, forming distinct reticulate pattern over dorsal surface, strongest anterodorsally; scales in lateral line scale row (L1) with dark blotch posteriorly, punctuated centrally by unpigmented lateral line canal (giving appearance of double dash line along lateral-line scale row); L+1 and L-1 pigment rows poorly developed or absent in juvenile individuals, represented by 12 well-developed dark brown spots along center of body (dorsal or ventral to scales 5–17 in lateral-line scale row) in largest individual examined; L+2 row absent; scaleless base of pectoral fin and scales adjacent to pelvic-fin origin peppered with small dark brown melanophores, forming distinct pectoral-base and indistinct pre-pelvic spots; lateral surface of snout, region rimming ventral margin of orbit and skin covering opercle densely scattered with dark brown melanophores; ventral surface largely devoid of pigment except for melanophores along anterior edge of rostral cap, small patch of brown melanophores situated beneath scales at anal-fin origin and a short line of melanophores posterior to anus, running along ventral midline from anus to 5th scale in scale row running between anus and anal-fin origin; dorsal surface of anterior pectoral- and pelvic-fin rays marked with small brown melanophores; dorsal fin with single, large, irregular, dark brown or black marking or multiple small dark brown or black markings along anterior margin, formed by melanophores scattered along fin membrane between last unbranched ray and anteriormost branched ray; anal fin hyaline; caudal fin with dark brown or black blotch over base of central caudal-fin rays and 2 well-separated dark brown markings on upper and lower lobes; often (also in holotype) anteriormost blotch along lower lobe and blotch over base of central caudal-fin rays confluent, forming irregular dark brown or black marking (Ref. 110241). In life: Body background colour pale golden brown; dorsal saddles and lateral stripe chocolate brown; lateral blotches and pigmentation on fins dark brown or black; scales in lateral-line scale row with a silvery iridescent spot at center, forming distinct iridescent dotted line along side of body; rays of pectoral fin and unbranched rays of pelvic fin pale yellow (Ref. 110241).
Biology:  Collected in swift flowing water of shallow to moderate (50-100 cm) depth over a substrate of sand and gravel; water parameters measured at this locality at time of collection include: 21C, pH 7.5, KH 3, GH 0 (Ref. 110241).
IUCN Red List Status: Not Evaluated (N.E.) Ref. (130435)
Threat to humans:  harmless

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