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First published online April 23, 2004
Journal of Experimental Biology 207, 1843-1853 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.00954
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Temperature induces gonadal maturation and affects electrophysiological sexual maturity indicators in Brachyhypopomus pinnicaudatus from a temperate climate

Laura Quintana1,*, Ana Silva1,2, Nibia Berois3 and Omar Macadar1

1 Depto de Neurofisiología, Instituto de Investigaciones Biológicas Clemente Estable, Unidad Asociada de Facultad de Ciencias–Universidad de la República, Avda, Italia 3318, Montevideo, Uruguay
2 Depto de Fisiología, Facultad de Ciencias-Universidad de la República, Montevideo, Uruguay
3 Sección de Biología Celular, Facultad de Ciencias-Universidad de la República, Montevideo, Uruguay

* Author for correspondence (e-mail: lauraq{at}iibce.edu.uy)

Accepted 24 February 2004

In contrast to most of the previous studies in gymnotiform reproduction, which have been conducted in the tropical region, this study examines a gymnotid from the temperate region in both the natural habitat and the laboratory. The gonadal histology of Brachyhypopomus pinnicaudatus is described for the first time. The male had a paired, lobular testis of the unrestricted spermatogonial type, and females a paired saccular cystovary. Analysis of gonads and their annual cycle enabled us to confirm the breeding season and to conclude that this species is a multiple spawner. Water temperature and photoperiod showed the expected annual cycles for the region. High temperature and a 14 h:10 h L:D photoperiod in the natural habitat coincided with (1) mature gonadal stages, (2) electrophysiological sexual dimorphism: males present a lengthened negative phase in their electric organ discharge (EOD) and (3) decreased temperature sensitivity of the EOD: the waveform does not change when temperature increases above 20°C. Acclimation to sustained high temperature (30 days, 28°C, 12 h:12 h L:D, low conductivity) induced gonad maturation along with EOD dimorphism. Our data show that high environmental temperature is enough to trigger sexual maturity in Brachyhypopomus pinnicaudatus from a temperate climate.

Key words: breeding, temperature sensitivity, electric fish, Brachyhypopomus pinnicaudatus, EOD






© The Company of Biologists Ltd 2004