Hoplias mbigua Azpelicueta, Benítez, Aichino & Mendez, 2015

Family:  Erythrinidae (Trahiras)
Max. size:  29.3 cm SL (male/unsexed)
Environment:  benthopelagic; freshwater,
Distribution:  South America: Argentina.
Diagnosis:  Dorsal soft rays (total): 14-15; Anal soft rays: 9-11; Vertebrae: -42. Diagnosis: the presence of tooth-bearing plates on dorsal surface of the basihyal and basibranchials and the medial margins of contralateral dentaries converging towards the mandibular symphysis in ventral view, includes the species in the H. malabaricus group; the presence of 5 brown bands transversely placed on lower jaw distinguishes the new species from its congeners, except H. microlepis (vs. lower jaw with small black or brown dots uniformly distributed or straight); the number of circunpeduncular scales in H. mbigua is 20 whereas H. teres and H. malabaricus have 18 circunpeduncular scales and H. microlepis 22-24, usually 24; Hoplias mbigua has convex dorsal profile between head and dorsal fin and large tooth plate on basihyal whereas H. teres has straight dorsal profile and smaller tooth plates on basihyal; Hoplias mbigua is distinguished from H. microlepis by the presence of 12-16 gill rakers on 1st epibranchial (vs. about 9) and 42-43 lateral line scales (vs. 43-47); Hoplias mbigua has a large supraopercle, with its anterior margin contacting the infraorbitals 5 and 6 whereas the lectotype of H. malabaricus has a short supraopercle, with an anterior margin scarcely extended before anterior opercular margin; Hoplias mbigua is distinguished from H. cf. malabaricus by the dorsal surface of head scarcely or strongly concave (vs. convex in H. cf. malabaricus); a large eye, with the upper margin of orbit strongly marked in skull roof (vs. lateral margin of skull scarcely concave at orbit); the shape of anterior profile of head angular in lateral view (vs. rounded), and the lower head depth 45-50 % of HL (vs. more than 50 % of HL); Hoplias mbigua has a large tooth-plate on basihyal and basibranchials instead of 2 lines of tooth-plates at sides of bones in H. cf. malabaricus; size or shape of basibranchial tooth-plate not observed in the radiograph of the H. malabaricus lectotype (Ref. 114112). Description: greatest body depth at vertical through posterior tip of pectoral fin; body cylindrical, deeper than wider; anterior profile of head angular in lateral view, markedly angular in larger specimens; dorsal profile of head always concave, in some large individuals concavity more pronounced; slightly convex or straight from vertical through 1st series of scales to dorsal-fin origin in large specimens, straight and postero-ventrally slanted under dorsal-fin base; slightly concave or straight from vertical through base of last dorsal-fin ray to origin of caudal-fin rays, independent from body size; ventral profile of head straight, slanted postero-ventrally; ventral profile of body slightly convex to pelvic-fin origin; approximately straight from latter point to anal-fin origin; straight and postero-dorsally oriented along anal-fin base; straight or slightly concave from base of last anal-fin ray to anterior most ventral procurrent caudal-fin rays; dorsal margin of orbit at same level of dorsal profile of head, eye surpassing that level in many specimens independent from body size; medial margins of contralateral dentaries forming a V shapped angle, sometimes not too abrupt; head wide, low; upper jaw shorter than lower jaw; posterior tip of maxilla surpassing posterior margin of eye, more than half of orbital diameter in large specimens (more than 240 mm SL); posterior portion of maxilla dorsally extended, covered by 2nd and 3rd infraorbitals; upper and lower lips fleshy with skin covering canines externally; anterior nostril tubular, separated from posterior; anterior and posterior nostrils located in an oblique low slit, with its anterodorsal origin at level of upper 3rd of orbit; posterior nostril located very close to eye; eye large, strongly entering in margin of skull roof; teeth in both jaws conical or canine; teeth and especially large canines completely covered by skin; premaxillary teeth in a single row, all teeth canines but varying in size; 1st premaxillary tooth large canine, followed by a 2nd tooth medium sized canine, 2 to 4 small canines, 1 medium-sized canine, 1 large canine, and 2 or 1 small canines; maxilla with single row, bearing 3 or 4 small canines followed by 1 medium-sized and largest one, 1 medium-sized and 30 to 40 small canines; number of small canines increasing during growth; dentary with anterior external row of teeth and posterior internal row; external series with 2 or 3 small symphysial canines followed by 1 medium-sized, and largest dentary canine, then several small or medium-sized canines and 2 larger; 1nternal series beginning immediately posterior to last conical tooth of external row and composed of numerous small canines, about 18; ectopterygoid and accessory ectopterygoid toothed; ectopterygoid with 1 series of small conical teeth along ventral margin and a patch of many smaller viliform teeth on ventromedial surface, occupying about 3/4 of its length; accessory ectopterygoid with a line of small external conical teeth and a ventral patch with viliform teeth; distal margins slightly rounded in all fins; dorsal-fin rays ii,12(15*), iii,12(1); dorsal fin located nearer snout tip than caudal fin ray origin; its origin at vertical 3 scales anterior to pelvic-fin origin; dorsal fin base a little more than twice length of base of anal fin; longest dorsal-fin ray approximately 80% of body depth; anal-fin base short with ii,7(1), iii,7(8), ii,8(1), iii,8(4*), iii,8(1), ii,9(1) rays; tip of adpressed dorsal fin falling near vertical through anal-fin origin or in same line; pectoral-fin rays with i,11(2), i,12(10), i,13(4*) rays; pectoral-fin origin located at a vertical through middle of subopercle; tip of pectoral fin separated from pelvic-fin origin by 3 to 4 scales in young specimens and 4 to 5 scales in larger ones; pectoral and pelvic fins of similar size although pelvic fin always scarcely longer than pectoral fin; pelvic-fin rays i,7(14*) or i,8(2); pelvic-fin origin situated at midbody, approximately in a vertical through 3rd or 4th dorsal-fin ray; tip of pelvic fin separated from anal-fin origin by 5 or 6 scales; caudal-fin rays i,15,i*; well-developed cycloid scales, imbricated along entire body; series of dorsal scales overlapping supraoccipital spine; last vertical series of scales on caudal peduncle forming a relatively straight line; 2 or 3 last rows of scales on caudal-fin rays smaller than those of body; anterior margin of scales undulated, with small notch at midpoint and posterior margin rounded; 8 to 12 radii extending from center of scale to its anterior margin and only 2 to 6 radii, extending from center of scale to its posterior margin; 1 to 3 incomplete radii in lateral field of many scales; lateral line straight and complete, extending from posteroventral margin of supracleithrum to middle caudalfin rays; last tube of lateral line in last scale; lateral line with 42(13*), 43(3) perforated scales; longitudinal series of scales between lateral line and dorsal-fin origin 6(15*), 5.5(1); longitudinal series of scales between lateral line and pelvic-fin origin 5(13*) 5.5(3); scales around caudal peduncle 20(15*, 1 specimen with 22) (Ref. 114112). Coloration: In life: dorsum brown, darker than rest of body; upper half of body dark brown and lower half scarcely lighter, sometimes iridescent; vent pale yellow; in many specimens (independent from body size), a white longitudinal band extending from posterior opercular margin to origin of lower caudal-fin rays, situated one scale below perforated scales; some specimens, with oblique brownish bands through white band; ground color of caudal fin dark, brown; remaining fins clear, brownish; all fins with pale yellow lines; remarkably 5-6 transverse brown bands in opercle; 6-8 brown ventral bands from symphysis to level of posterior infraorbital margin; presence of bands in all specimens from 45 mm SL to largest 293 mm SL (Ref. 114112). Color in alcohol: ground coloration of body dark to light brown, darker dorsally and paler ventrally; ventral region light yellow; many scales covering vent with a pale brown dot usually located in anterior portion of scale, more numerous in large specimens, with different shape; in most specimens flanks with a dark longitudinal band along perforated line scales, covering approximately half of the series immediately above and below lateral line; also, most specimens with a light band below dark band; sometimes oblique dorsoposterior dark stripes occupying portions of light band dorsal surface of head dark brown, lateral faces lighter; sometimes, 2 or 3 bands radiating ventrally and posteriorly from eye through infraorbitals; 1st on infraorbital 2, 2nd band on infraorbital 3; 3rd, when present, on infraorbital 5, sometimes continued through opercle; lateral and ventral surface of dentaries with 5-6 transverse brown bands, many times also visible on maxilla; those bands extended on angular, retroarticular, subopercle, interopercle, and branchiostegal membranes; brown bands present independent from body size; many times opercle marbled, opercular membrane dotted; 1 small dot in dorsal half of caudal peduncle, near caudal-fin ray origin; caudal fin dark brown, with pale yellow bands; dorsal, pectoral, and pelvic fins pale with numerous dots forming dark bands; all fins clear in few specimens; bands on anal fin more regular than those on remaining fins; chromatophores of pectoral and pelvic fins located on dorsal and ventral surfaces of fins with similar pattern (Ref. 114112).
Biology: 
IUCN Red List Status: Not Evaluated (N.E.) Ref. (130435)
Threat to humans:  harmless


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