Avoidance behavior and brain monoamines in fish

Brain dopaminergic activity increased in telencephalon and decreased in the brain stem following skin extract exposure, again independent of availability of hiding material. However, fish kept in aquaria without hiding material showed an elevation of serotonergic activity in the brain stem and the optic tectum compared to fish with available hiding material. Absence of hiding material increased serotonergic activity also without exposure to skin extract. In aquaria with hiding material, the fish stirred up a cloud of fine sediments and showed a more pronounced decrease in locomotor activity in agreement with this being a more efficient freezing or immobile avoidance behavior. These results show that basic components of avoidance behavior and related brain changes are present in the fish brain, in accordance with the common phylogenetic roots of avoidance behavior in all vertebrates.