Archolaemus blax Korringa (Pisces, Gymnotiformes, Sternopygidae); a redescription with notes on ecology By Horst O. Schwassmann Department of Zoology University of Florida and Mirian L. Carvalho Museu Paraense E. Goeldi/CNPq Abstract Archolaemus blax, previously known only from the Tocantins drainage in Brazil, is reported from many areas of the Brazilian and Guyana pre-Cambrian shields. Populations of this species inhabit rock aggregates of rapids. The fish spend the day inside crevices and emerge at night to forage mainly on larvae of Diptera. Spawning activity was noted during the transition from dry to rainy seasons (October-November) in the Serra Carajäs. Like other gymno-tiforms, Archolaemus is a partial spawner. It is closely related to Eigenmannia anatomically as well as in its electric organ discharge frequency and pulse shape. The presence of extra-oral dentary teeth, stated as diagnostic in the ori-ginal description by KORRINGA (1970), could not be verified in any of the 66 specimens available for the purpose of this redescription. Introduction Archolaemus blax was originally described by Korringa (1970) on the basis of three specimens from the Upper Tocantins River in the Brazilian State of Goias. Close affinities with Eigenmannia and Ster-nopygus place the new genus in the family Sternopygidae, as recently delimited by Mago-Leccia (1978). New material from different localities has been collected since, greatly extending the geographic rän-ge. In addition, a study of a population in the field has provided Information about ecological aspects. Material and Methods The specimens utilized for this study are on deposit at the Museu Paraense E. Goeldi, Belem, Parä, Brasil (MPEG), the Museu de Zoologia, Universidade de Säo Paulo, Säo Paulo, Brasil (MZUSP), the Instituto Nacional de Pesquisas da Amazonia, Manaus, Amazonas, Brasil (INPA), and the California Academy of Sciences, San Fran-cisco, California, U.S.A. (CAS). The systematic part is based on 70 specimens, 66 of which were closely examined and measured while 27 were used in the analysis of morphometric and meristic data. Radiographs were obtained from three specimens (MPEG 1369), and of the type and one paratype (CAS 24743, 24744). Measurements were made by ruler for total and Stan-dard lengths (TL and SL) to the nearest millimeter, and by calipers for the other dimensions to the nearest tenth of a millimeter. A population of 19 recognized Archolaemus was monitored over 24 hours and was revisited on several other oc-casions. Specimens were located in their day-time hiding places by a device consisting of a pair of metal electrodes 231
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