Predator exposure alters brain serotonin metabolism in bicolour damselfish

The effect of predator exposure on brain serotonin utilization was studied in bicolour damselfish (Pomacentrus partitus). Predator exposure (lasting 2 h), which took place in an aquarium where a transparent wall separated the damselfish from the predator (a graysby, Epinephelus cruentatus), resulted in increased concentrations of 5-hydroxyindoleacetic acid (5-HIAA, the main serotonin metabolite) and 1.6-1.8 fold elevations of 5-HIAA/serotonin ratios (an index of serotonergic activity) in telencephalon, hypothalamus and brain stem. The results show that predator exposure, like intraspecific social stress, induces increased brain serotonergic activity in fish. Different types of stress also elevate brain serotonergic activity in mammals, indicating that this is a phylogenetically very old stress response, possibly helping the animal's coping response.