Hemigrammus arua Lima, Wosiacki & Ramos 2009

Distinguished from all species of the genus, except Hemigrammus stictus (Durbin), by having a large single humeral spot situated from fifth-sixth to posterior margin of eighth-tenth lateral line scales. Differs from Hemigrammus stictus by having a humeral spot roughly rectangular, higher than wide, with a pronounced upper, anteriorly-oriented extension,conferring an inverted-comma shape to the blotch (vs. humeral spot roughly rounded, not presenting an inverted-comma shape), and life color pattern presenting unpaired fins orange reddish (vs. caudal fin and caudal peduncle bright red in life, remaining fins translucent) (Ref. 81198).Description: Dorsal-fin rays ii, 9, 10, not including small ossification anterior to first unbranched ray, discernible only in c&s specimens, absent in two out of eight c&s individuals; anal-fin rays iv, 17-21; pectoral-fin rays i, 9-11; pelvic-fin rays typically i,7, a single specimen i,8 (Ref. 81198).

Dorsal soft rays (total): 11 - 12; Analsoft rays: 21 - 25; Vertebrae: 31

Inhabits shallow marginal areas, with abundant aquatic macrophytes, both emergent and non-emergent (Ref. 81198). Gut contents of four specimens include insect larvae, winged insects and plant matter (Ref. 81198).

Conhecido de áreas rasas e com vegetação aquática de lagos de ria e igarapés de águas escuras (Lima et al., 2009). Dieta observada como sendo composta por insetos (aquáticos e terrestres) e matéria vegetal (Lima et al., 2009).

Apenas conhecida de tributários do rio Arapiuns (afluente do rio Tapajós) e Juruti Grande (afluente do rio Amazonas), Pará, Brasil.