Animals

Experiments were performed in adult (5–15  months old) zebrafish (Danio rerio). Fish of both sexes were used in an approximately 50:50 ratio to minimize potential sex-dependent biases. Fish were bred under standard laboratory conditions (26–27°C, 13  hr/11  hr light/dark cycle). All experiments were approved by the Veterinary Department of the Canton Basel-Stadt (Switzerland).

The following transgenic fish lines were used: Tg[gad1b:GFP] (Satou et al., 2013), Tg[gad1b:Gal4] (Frank et al., 2019), Tg [vglut2a:loxP-DsRed-loxP-GFP] (Satou et al., 2013), Tg[th:Gal4] (Li et al., 2015), Tg[vglut1:GFP] (created in this study), Tg[vglut1:Gal4] (created in this study), Tg[UAS:tdTomato-CAAX] (Miyasaka et al., 2014), and Tg[UAS:TVA-mCherry] (created in this study). Note that Tg[gad1b:GFP] and Tg[gad1b:Gal4] were created using the same BAC (zC24M22).

Optogenetic experiments and odor discrimination training were performed in fish with low pigmentation that were derived by selection from a wildtype population. We refer to this genetic background as ‘Basel-golden’. These fish facilitate non-invasive optical access to the brain in adults and show no obvious impairments or behavioral alterations.