Date Published: January 28, 2019
Publisher: Public Library of Science
Author(s): Alessandra Bono, Luiz Fernando Caserta Tencatt, Felipe Alonso, Pablo Lehmann A., Zuogang Peng.
A redescription of Corydoras undulatus Regan, 1912 is presented. The original description of C. undulatus is very succinct, as is its diagnosis, which is based only on external morphology. Additional information in the scientific literature on this species is scarce. Specimens from the distribution area of this species were analyzed; Paraná and Paraguay river basins in Argentina, Uruguay river basin in Argentina, Brazil and Uruguay, and the Laguna dos Patos system in Brazil. Morphological analysis, principal component analysis (PCA), meristic comparison and osteological description were performed. Corydoras undulatus can be distinguished from its congeners mainly by having the following combination of characters: mesethmoid short, with anterior tip short, smaller than 50% of the entire bone length; posterior margin of the pectoral-fin spine with nearly all serrations directed towards origin of spine; pectoral-fin spine with conical serrations; and its peculiar color pattern. The analysis of the material from the different basins did not indicate relevant morphological differences, suggesting that the species presents a wide distribution in La Plata and Laguna dos Patos drainages. The shared geographic distribution between these two systems is also present in other fish species. The current work presents data about the type locality, taxonomy, osteology, distribution and ontogenetic variation of color pattern in C. undulatus. Comments on the identity of a very similar congener, Corydoras latus, will also be provided.
Corydoras Lacépède, 1803 comprises the majority of species of the Corydoradinae, and represents the genus with the greatest species-rich among the Siluriformes. With 174 valid species, 19 described in the last ten years, besides presenting many species not yet described [1,2].
The live specimens were anesthetized in a Eugenol solution dissolved in ethyl alcohol in 1:9 ratio (clove oil: ethyl alcohol), and this solution was then diluted with water in order to obtain concentrations of 0.20 mL of clove oil per 500 mL of water. To follow, specimens were fixed in 10% formalin, and then transferred to 70% ethanol. This protocol has been approved by the commission of ethical use of animals of Universidade do Vale do Rio dos Sinos (CEUA/UNISINOS) which considerers animal welfare laws. The morphological measurements were obtained using a precision digital caliper in tenths of millimeters. Meristic and morphometric data were taken following Reis  with modification of Tencatt et al. . Morphometric measures are presented as percentages of standard length (SL) and head length (HL). Based on the morphometric data, Principal Component Analysis (PCA) was performed with PAST 1.0 statistical program. Some specimens were cleared and stained (c&s) following Taylor & Van Dyke . The homology of the barbels follows Britto & Lima . The osteological terminology was based on Reis , except for the parieto-supraoccipital instead of the supraoccipital , the pterotic compound instead of the supracleithrum  and the scapulocoracoid instead of the coracoid . The nomenclature of the lateral-sensory canals and the preopercular pores is in agreement with Schaefer & Aquino  and Schaefer , respectively. The supra-preopercle sensu Huysentruyt & Adriaens  was treated here as a part of the hyomandibula. Vertebral counts include only free vertebrae, with the compound caudal centra (preural 1+ ural 1) counted as a single element. The stripes were counted as in Tencatt & Ohara .
According to Regan, the type locality of C. undulatus is “La Plata”, without further details. However, “La Plata” could refer to the city of La Plata in Buenos Aires or to the La Plata basin. Specimens of C. undulatus were searched in main Argentinean collections (MACN, MLP, FA, IBIGEO, FML), and it was not possible to find any lot of Corydoras undulatus from La Plata city, neither from the left bank of La Plata River basin or the Pre-Delta of Paraná area in any ichthyological collection. It is worth noting that in this area there have been ichthyologists since the late XIX century, and in La Plata city itself. Additionally, the specimens in which the description was based were donated by JP Arnold and WG Wolterstorff. Neither these people are known to have been in South America. Furthermore, Johann Paul Arnold (1869–1952) was a German aquarium hobbyist who forwarded numerous fish specimens taken from commercial aquarium imports to Germany to ichthyologist for identification . Willy Georg Wolterstorff (1864–1943) was a German paleontologist and herpetologist . Therefore, those specimens were more probably imported as aquarium fish and donated to Regan and the type locality should be considered as uncertain, probably from somewhere in “La Plata” basin. Most likely places are those from southern Entre Ríos where this species is commonly found and are close localities to the Port of Buenos Aires where is the most likely place where those fish were shipped to Europe.