同じ海域に分布するNetuma planifronsとは鰓耙の長さ,口裂の大きさなどの形質の組合せで区別できる(Higuchi, Reis and Araujo, 1982)。
(稲田伊史)
Material examined:
2 from Argentina (263.0-322.0 mm SL), FSFL EL 825, 826.
Description:
D T 7; A 14-15; P1T, 10; P2 6; GR 5+1+10=16.
HL 27.5-27.7% of SL; ED 3.6-4.1; BD 20.8-21.3; SN 11.4; IO 12.4-13.4; UJ 8.7-9.2; P1L 19.1-21.7; P2L 14.3-14.5.
Body elongate, head depressed and posterior part of body compressed. Snout bluntly rounded. Mouth terminal to inferior; lower jaw included under upper jaw when closed. Teeth on both jaws fine and granular, forming villiform bands; teeth on vomer and palatine arranged in wide bands and closely situated each other. Distance between both left and right anterior nostrils shorter than distance between anterior nostril and middle part of eye; anterior nostril small and round, and posterior one larger with flap. Head covered by a rugose bony shield. No fleshy furrow extending between nostrils. A longitudinal fleshy groove in median depression of head. Three pairs of barbels around mouth, all round in cross section; one pair of maxillary barbels extending to base of pectoral fin; two pairs of mental barbels situated below lower jaw. End of dorsal fin base situated anterior to anal fin base. Dorsal fin short, with a long spine (18.2-18.8% of SL); dorsal and pectoral spines strongly serrated. A well developed adipose fin present. Anus between both pelvic fins. Gill-rakers short, weak and distributed along first two gill-arches. Gill-membranes fused with each other and attached to isthmus. Scales absent. Dorsal part of body dark blue and ventral silvery white. Dorsal fin, adipose fin, soft ray of pectoral fin and maxillary barbel dark blue. Posterior margins of caudal and anal fins slightly blackish.
Distribution:
Coastal waters from Rio Grande do Sul of southern Brazil to the mouth of La Plata of Argentina.
Remarks:
This species differs from the sympatric species, Netuma planifrons by the combination of such characters as the length of gill-rakers and width of mouth (Higuchi et al., 1982). Tachysurus was often adaped to this fish (Fowler, 1951; Stehmann, 1978).