Temperature induces gonadal maturation and affects electrophysiological sexual maturity indicators, in Brachyhypopomus pinnicaudatus from the temperate climate. 2004.

L. Quintana, A. Silva,  N. Berois & O. Macadar.

Journal of Experimental Biology, 207, 1843-1853.

 Most of the previous studies in gymnotiform reproduction have been conducted

in the tropical region whereas our data have been collected in the temperate

region, at the southern boundary of gymnotiform distribution in America. Male

Brachyhypopomus pinnicaudatus present a paired, lobular testis of the unrestricted

spermatogonial type, and females a paired saccular cystovary. Analysis of gonads

and of their annual cycle allowed us to confirm the breeding season and conclude

this species is a multiple spawner. Water temperature and photoperiod showed the

expected annual cycles for the region. High temperature and 14 hL: 10 hD 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) the decrease of temperature sensitivity of EOD: the

waveform does not change when temperature increases over 20ºC. Acclimation to

sustained high temperature (30 days, 28ºC, 12 hL: 12 hD, 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 of the temperate climate.