Effect of season on cell proliferation in different brain regions of field active Brachyhypopomus gauderio. The anterior midbrain comprises sections 17–19 and the posterior midbrain comprises sections 14–16, according the Maler brain atlas (Maler et al., 1991). EGm, eminentia granularis pars medialis; ELL, electrosensory lateral line lobe; Pn, pacemaker; PVZ, periventricular zone. Whole section is the density of BrdU+ cells in the whole transverse section. Background is the density of BrdU+ cells in the transverse section outside of proliferative zones (PVZ and EGm). Cell proliferation was significantly higher (P<0.0001) during the breeding season than during the non-breeding season in all brain regions. N=6–8 fish per sample.