Pimelodus microstoma Steindachner, 1877, a valid species of pimelodid catfish (Siluriformes: Pimelodidae) from the upper rio Paraná drainage

Pimelodus microstoma, which has been treated as a junior synonym of P. fur, is resurrected and its type locality restricted to Irisanga (=Orissanga), Sao Paulo State, in the upper rio Parana. An identification key is provided for Pimelodus species from the upper portions of the Parana drainage.

Pimelodus microstoma was described based on three specimens collected by the Austrian naturalist Johann Natterer, who conducted many collection expeditions in Brazil from 1818 to 1835.Some Pimelodus specimens collected by Natterer were initially treated as P. maculatus La Cépède, 1803 by Kner (1858), until Steindachner (1877) recognized them as representatives of an undescribed species which he formally named P. microstoma.Steindachner (1877) was aware that specimens came from Natterer's collections and referred to the type locality as "Brazil, von Irisanga [=Orissanga, São Paulo], Rio Branco und Barra do Rio Negro."The occurrence of such a wide distribution (Amazon and Paraná basins) is unlikely for a Pimelodus species.
The examination of the type series of P. microstoma demonstrated that all syntypes are co-specific, and its comparison with the type series and/or specimens of Pimelodus species from the Amazon drainage, allowed its recognition as a valid and distinct species.Pimelodus microstoma is distinguished from all Amazonian Pimelodus species, and from recently described Pimelodus species from rio São Francisco (Ribeiro & Lucena, 2003), by the combination of the following characters: a deep, robust body; relatively long adipose fin, occupying at least half of the distance between the end of the dorsal-fin base and the beginning of the caudal peduncle; prominent upper jaw, allowing the visualization of nearly the whole premaxillary tooth plate; small mouth and a short maxillary barbel, usually not reaching the base of the caudal peduncle; and a gray uniform color pattern with only a few dark dots (sometimes very weak or absent) in the antero-lateral region.
Johann Natterer's journey in Brazil included many Brazilian states other than Amazonas: São Paulo, Paraná, Minas Gerais, Goiás, Mato Grosso, and Pará (Papavero, 1971).Therefore, it is possible that syntypes of P. microstoma were captured in the drainages of the rios São Francisco, Paraguay and Paraná.The comparison between these syntypes with Pimelodus specimens from the aforementioned drainages showed many differences, mainly color pattern ones.In the next paragraphs, we discuss the diagnostic characters of P. microstoma that warrant its validity and distinctiveness from its congeners inhabiting the rio Paraná and neighboring drainages.
Although Natterer himself did not collect specimens in the rio São Francisco drainage, Dr. J. E. Pohl, one of the scientists who joined Natterer in Brazil to form the Austrian Mission -collected around the cities of Pirapora and Barra do Rio das Velhas (currently Guaicu), both in the rio São Francisco basin (Papavero, 1971).Pohl's collections arrived in Vienna in four consignment contents, which included 42 fish specimens among other zoological groups (Riedl-Dorn, 1999).
It is important to point out that a specimen from Juazeiro, Bahia (MZUSP 24723) was found to be very similar to P. microstoma.Despite the large number of specimens examined from the rio São Francisco drainage, only this specimen possessed the color pattern typical of P. microstoma.We prefer to regard it provisionally as Pimelodus sp., since a more encompassing analysis is beyond the scope of this work.
Eight species were originally described or cited for the drainages of the rio Paraguay or lower rio Paraná (including the rio Iguaçu): Pimelodus maculatus, P. albicans (Valenciennes, 1840), P. argenteus Perugia, 1891, P. brevis Marini, Nichols & La Monte, 1933, P. ortmanni Haseman, 1911, P.  absconditus Azpelicueta, 1995, P. mysteriosus Azpelicueta, 1998, and P. atrobrunneus Vidal & Lucena, 1999.Pimelodus maculatus has a spotted body (vs.gray or few spots restricted to the antero-dorsal region of the body in P. microstoma).Like P. microstoma, Pimelodus albicans has teeth on the vomer but can be distinguished by the longer maxillary barbels, reaching the middle of anal fin, and a uniform brownish color pattern or, according to Eigenmann & Eigenmann (1890), by three dark longitudinal stripes in young specimens.Pimelodus brevis has a short body, smaller eye (6.4 vs. 3.7-3.8times in HL) and does not exhibit dots on the body flanks (the holotype is missing, and thus comparative analysis was according to Marini et al., 1933).Pimelodus ortmanni has comparatively longer dots, forming 3-5 rows on the lateral surface of the body, and on fins.Pimelodus absconditus has thick and fleshy, well-developed lips.Pimelodus mysteriosus has spots in three or four rows along the body and a very long maxillary barbel, reaching the tip of caudal-fin lobes.Pimelodus argenteus and P. atrobrunneus do not have a spotted body.
Three species were originally described for the upper rio Paraná -P.paranaensis Britski & Langeani, 1988, P. heraldoi Azpelicueta, 2001, and P. platicirris Borodin 1927.Pimelodus microstoma can also be distinguished from these species by the same combination of characters cited above.Pimelodus heraldoi has dots arranged irregularly on the body, forming 8-9 rows.Pimelodus platicirris has 3-5 rows of dots on lateral surface of the body and dorsal and caudal fins.Pimelodus paranaensis has very small dots on the body sides and a premaxillary tooth plate with pointed postero-lateral corners (vs.rounded in P. microstoma).
During survey analyses of Pimelodus specimens housed in the fish collection of MZUSP, the senior author concluded that some upper rio Paraná specimens (see Material Exam-ined) are very similar to the syntypes of P. microstoma (see Morris & Sabaj, 2006 for images of the syntype NMW 45824.1)regarding morphometrics, meristics, and chromatic features (Fig. 3).Therefore, we assigned these specimens the species name P. microstoma and restricted its type locality to Orissanga, São Paulo State, upper rio Paraná basin (thereby removing the species from the list of the fishes of the rio Amazonas drainage).Below we provide a provisional key to Pimelodus species from the upper rio Paraná.