Moenkhausia, Eigenmann, 1903

Mirande, Juan Marcos, Koerber, Stefan, Terán, Guillermo E. & Aguilera, Gastón, 2020, Who’s behind those red eyes? The Moenkhausia oligolepis group in Argentina (Characiformes: Characidae)., Ichthyological Contributions of PecesCriollos 66, pp. 1-7 : 2-3

History of red-eyed Moenkhausia in Argentina

In their account for Moenkhausia sanctaefilomenae (Steindachner, 1907) , Ringuelet et al. (1967) provided a list of references including Steindachner’s original description, the record of Poecilurichthys agassizii by Eigenmann & Kennedy (1903) from Paraguay, M. sanctaefilomenae from Eigenmann (1917), and Meinken (1937) as the first record from Argentina. In general, Tetragonopterus agassizii Steindachner, 1876 is considered to be a possible, uncertain synonym of Moenkhausia oligolepis ( Fricke 2020) . Yet, especifically the specimens mentioned by Boulenger (1900) as Tetragonopterus agassizii (not Steindachner) and by Eigenmann [& Kennedy] (1903) under Poecilurichthys agassizii (not Steindachner) have been assigned to M. australis by Reia (2019).

Surprisingly, in the list of Ringuelet et al. (1967) Boulenger’s record of Tetragonopterus agassizii was not included. Boulenger (1897) reported on specimens collected by Borelli in San Lorenzo, Jujuy, a place not found in any modern map. A ‘hacienda San Lorenzo’ in the past was one of the largest in Jujuy ( Ferreiro 2016, Peirotti 2007) and today is located in the town of Calilegua ( Fernández 2010) in Jujuy, right at the banks of San Lorenzo river, an affluent to San Francisco river which drains to the Bermejo river .

Boulenger made an interesting comment on the specimens of Tetragonopterus agassizii he examined: ”Chez le plus grand nombre des spécimens (jeunes) la ligne latérale ne s’étend que sur quelques unes des écailles antérieures; chez d'autres, elle est complète.” Translated, ‘In the largest number of specimens (young) the lateral line only extends over a few anterior scales; in others it is complete’.

This comment may have been the basis for Eigenmann’s statement on differences in the lateral line between young and adult specimens, which then lead him to synonymize M. australis with M. sanctaefilomenae . By our actual knowledge Boulenger may have examined a mixture of specimens compound by both, M. australis and M. forestii . If Boulenger (1897) shall be considered as first records of both species from Argentina, may only be clarified after examining the respective specimens, if still existing.

Background of the specimens from Meinken’s first record (1937)

Still today many descendants of German immigrants to Argentina maintain tight connections to the native country, language and culture of their ancestors, sending their children to one of the German schools, being members in German sports clubs, worship in German language churches etc. The second author’s in-laws still practice all the above and speak German at home, being the fourth generation from great-grandparents who arrived to Buenos Aires between 1880 and 1905.

Those still existing bonds have surely been yet much stronger in the 1930ies when most German-Argentineans were the first generation born in South America. This was most probably the case for Carlos Hahn from Corrientes city, the collector of those specimens of red-eyed Moenkhausia Meinken’s report (1937) was based on. By his family name and the perfect German writing there is no space for doubts that he was son or grandson of German and/or Austrian immigrants, but the fact that he published under the first name ‘Carlos’, not as Karl or Carl, indicates that he was part of this Argentina-born generation. Having stated in 1934 that 17 years earlier he was a high school student when breading Xiphophorus helleri , Macropodus opercularis , and Pterophyllum scalare in aquaria (1934a), it can be assumed that Carlos W. Hahn was born around 1902.

In his hometown Corrientes he started to keep in aquaria the species he could find in the neighborhood and for identification he sent preserved specimens to Meinken , editor of ‘ Blaetter für Aquarien- und Terrarienkunde’, one of the five aquarium journals then existing in Germany. Their cooperation resulted in publications of three different types: notes published by Hahn himself (1934a, 1934b, 1935, 1936), articles published by Meinken based on specimens received from Hahn (1935, 1936a, 1937), and six letters from Hahn to Meinken, subsequently published by Meinken (1936b, 1936c).

It is noteworthy that among the notes from the second group, Meinken (1936a) published a report on Melanorivulus punctatus , (sub Rivulus sp. , similar but not identical to R. strigatus ) based on a report and drawing received from Hahn. This was in fact the first record for this species from Argentina, and not the paper of Alonso de Arámburu et al. (1962, sub R. strigatus ) as stated by later authors ( Ringuelet et al. 1967, López et al. 2003, Mirande & Koerber 2015).

From the specimens received from Hahn, Meinken described several new species: Farlowella hahni , Leporinus nigripinnis (a synonym of Abramites hypselonotus ), Leporinus platycephalus (a synonym of Schizodon borellii ), and Rhamphichthys hahni . It is doubtful that Hahn collected the type specimen of Farlowella paranaense (a synonym of F. amazonum ) in Corrientes and more probable that Meinken mixed up labels ( Azpelicueta & Koerber 2015).

Other specimens sent by Hahn were not considered as new to science by Meinken, but have been the basis for first records from Argentina published by him: Leporinus striatus , Hyphessobrycon eques (sub H. serpae ), Sternopygus macrurus , Rineloricaria parva , Hypostomus latifrons (sub Ancistrus vittatus ), Otocinclus vittatus , Bujurquina vittata (sub Aequidens paraguayensis ), and Moenkhausia sanctaefilomenae , the subject of the present note.