first record from Argentina:
Gymnorhamphichthys britskii Carvalho, Ramos & Albert, 2011

distribution (from publication):
Gymnorhamphichthys britskii is known from tributaries of the Río de La Plata system. It is known from the upper and lower Paraguay basins in Paraguay and Brazil, and the lower Paraná basin in Paraguay, Brazil, and Argentina (no records from Uruguay basin. The presence of this species in the Upper Paraná was likely caused by the formation of the Itaipu reservoir, which allowed dispersal into upstream portions of the Paraná through the former Sete Quedas waterfalls.

published in:
Carvalho, T.P., C.S. Ramos & J.S. Albert (2001):
A New Species of Gymnorhamphichthys (Gymnotiformes: Rhamphichthyidae) from the Paraná–Paraguay basin.
Copeia 2011 (3): 400-406

abstract (from publication):
Gymnorhamphichthys britskii, new species, is described from the Paraná-Paraguay system. The new species is distinguished from all other congeners except G. hypostomus in having 5–16 (usually 9–13) large dark saddle-shaped pigment bars over the dorsal midline, extending between the nape and a vertical with the end of the anal fin, and sometimes reaching to or slightly below the lateral line. The new species differs from G. hypostomus in having 141–172 vs. 178–211 anal-fin rays; a shorter snout, preorbital distance 48.1–60.3 of head length (mean 54.6 ) vs. 58.3–68.6 (mean 63.9); a larger eye, diameter 5.7–9.0 of head length (mean 7.0 ) vs. 3.3–5.9 (mean 4.3 ); a longer distance from tip of snout to posterior nares, 17.1–22.0 of head length (mean 19.2 ) vs. 11.2–17.1 (mean 13.8 ); 7 vs. 9–13 displaced hemal spines; and 64–69 vs. 71–75 vertebrae to end of anal fin.

The description includes non-type material from Entre Ríos and Corrientes, Argentina.