It is widely documented that the timing of reproduction is
controlled by external signals such as seasonal changes in day-length
or photoperiod, chemosensory cues from con-specifics, food availability
and temperature. Timing of breeding to an optimal season is a
requirement for a successful reproductive outcome, and many
organisms evolved to use changes in photoperiod as the primary
signal that coordinates the breeding season [1,2]. Photoperiodic
signals are capable of modifying the excitability of GnRH neurons
which are the command cells in the central nervous system that
control reproductive physiology and behaviour in all vertebrates
studied to date [3]. Photoperiod alters morphological characteristics
of both GnRH neurons and glia that surround GnRH-neuron axon
terminalis in Japanese quail [4]. It was also shown that photoperiod is
capable to alter synaptic inputs to GnRH neurons in sheep [5]. In male
masu salmon it was shown that photoperiod influences the
expression of GnRH mRNA [6]. Recently, in the atheriniform fish
pejerrey Odontesthes bonariensis it was shown that the increase in day