Key to the species of Hisonotus from the laguna dos Patos system

1. Dorsad and ventrad series of odontodes along anterior margin of the snout separated by a narrow or wide odontode-free band...............................................................2

1’. Odontode-free band absent on anterior margin of snout, which is completely covered by odontodes.....................11

2. Tuft of enlarged odontodes present on the parietosupraoccipital tip, odontodes in that region approximately four to five times larger than the ones in surrounding areas...............................................................3

2’. Tuft of enlarged odontodes absent on the parietosupraoccipital tip, odontodes in that region approximately the same size or slightly larger than the in surrounding areas............................................................4

3. Pectoral-fin spine short (22.0-25.6% of SL, mean 24.0%), just reaching the vertical through dorsal-fin origin; general color pattern in life, dark green; in alcohol gray ..................................................................... Hisonotus prata (rio da Prata, in the rio Taquari drainage).

3’. Pectoral-fin spine long (24.7 -29.0 % of SL, mean 26.7%), far surpassing the vertical through dorsal-fin origin; general color pattern in life yellowish brown; in alcohol yellow to light brown........................... Hisonotus carreiro (rio Carreiro, in the rio Taquari drainage)

4. Three predorsal plate series; 22-25 plates in median series; and 27-29 vertebrae.............................................................5

4’. Three or four predorsal plate series (modally four); 25-29 plates in median series; and 30-32 vertebrae......................9

5. Caudal fin with paired, somewhat triangular, hyaline areas at the middle portion of ventral and dorsal lobes .................................................................... Hisonotus vireo (rio Jacuí basin)

5’. Caudal fin mostly dark, or with a transversal hyaline band at the midventral portion.......................................................6

6. Posterior portion of perforated lateral line absent; median abdominal plate series composed of several small plates, irregularly arranged.................... Hisonotus nigricauda (laguna dos Patos and rio Uruguay basin).

6’. Posterior portion of perforated lateral line present; median abdominal plate series absent or composed of larger plates, arranged in one to three series.............................................7

7. Caudal fin with one or two transversal hyaline bands............................................ Hisonotus charrua (headwaters of rio Piratiní and rio Jaguarão drainage).

7’. Caudal fin mostly dark, without transversal hyaline bands......................................................................................8

8. Median abdominal plate series present, formed by one or two series of median to large plates; median lateral plate series truncated, not reaching the posterior end of caudal peduncle............................................... Hisonotus brunneus (upper rio Jacuí drainage).

8’. Median abdominal plate series absent, scattered platelets at preanal shield region; median lateral plate series not truncated, reaching the posterior end of caudal peduncle ................................................... Hisonotus heterogaster (lower rio Jacuí drainage).

9. Caudal peduncle slightly square in cross section; odontodefree band on snout wide; rostral plate thin without the posterior notch articulation for the mesethmoid; prenasal area covered by plates.................. Hisonotus notopagos (headwaters of rio Camaquã drainage).

9’. Caudal peduncle round in cross section; odontode-free band on snout narrow; rostral plate thick with a posterior notch articulation for the mesethmoid; prenasal area naked, without plates.......................................................................10

10. Body relatively slender; shallow at dorsal-fin origin (body depth 13.3-16.3% in SL, mean 15.1%)... Hisonotus taimensis (lower portions of laguna Mirim tributaries)

10’. Body relatively robust; deep at dorsal-fin origin (body depth 16.2-20.8 % in SL, mean 18.1%).......... Hisonotus laevior (laguna dos Patos system)

11. Posterior portion of perforated lateral line absent; plates in median abdominal series small and irregularly arranged ..................................... Hisonotus nigricauda (lower portions of laguna dos Patos system and rio Uruguay basin).

11’. Posterior portion of perforated lateral line present; plates in median abdominal series large and regularly arranged, usually in a single row........................................................12

12. Caudal fin with one or more transversal hyaline bands; dorsal surface of head and body with dark marks contrasting with dark and white, vermiculous to ovoid, spots................................................ Hisonotus armatus (laguna dos Patos system).

12’. Caudal fin mostly dark, without a transversal hyaline band, or sometimes presenting an inconspicuous band; dorsal surface of head and body yellowish to pale brown................................... Hisonotus leucofrenatus (coastal drainages of southeastern and south Brazil from Ribeira de Iguape basin to eastern coastal plain of laguna dos Patos).