Effects of carbamazepine on cortisol levels and behavioral responses to stress in the fish Jenynsia multidentata

•Restraint stress disrupts scototaxis and increases cortisol in Jenynsia multidentata•In the light/dark test, CBZ decreases cortisol in fish under restraint stress•CBZ at its lowest concentration reduces behavioral endpoints in stressed fish•In the shoaling test, neither CBZ nor stress modify shoaling behavior or cortisol•CBZ induces diverse responses depending on test, concentration or endpoint evaluated

Carbamazepine (CBZ) is an anticonvulsant drug, prescribed worldwide for the treatment of epilepsy, bipolar disorder and trigeminal neuralgia, which has been frequently detected in aquatic environments. The objective of this study was to analyze if CBZ modifies scototaxis and shoaling behaviors and/or whole-body cortisol levels of the one-sided livebearing fish Jenynsia multidentata under stress condition. Female adults of J. multidentata were exposed to 0, 10, 50 and 200 μg CBZ/L during 14 days. After CBZ exposure, fish were subjected to restraint stress during 15 min. Control animals were not exposed to CBZ or stress. In the light/dark preference test (scototaxis), the individuals under acute restraint stress (without CBZ) exhibited a significant increase in the mean speed and in the time spent both in the light compartment and in the bottom of the tank with respect to controls. They also showed a tendency to stay longer frozen in the light compartment. Fish exposed to 10 and 50 μg CBZ/L showed a significant reduction in mean speed compared to stressed fish without CBZ. A reduction in the time spent in the bottom of the tank was also observed in fish exposed to 10 μg CBZ/L. Fish exposed to 200 μg CBZ/L showed a decreasing tendency in all behavioral endpoints (time spent in the light compartment, mean speed, time spent at the bottom and freezing) in comparison to stressed fish not exposed to CBZ. Considering whole-body cortisol results, fish under acute restraint stress (without CBZ) significantly increased their hormone levels with respect to the control group, while fish exposed to CBZ and acute restraint stress, significantly decreased their whole-body cortisol levels. There were no significant changes in shoaling behavior due to either stress or CBZ exposure and no significant differences in whole-body cortisol levels between experimental groups. Considering that the light/dark and shoaling tests measure different stress response behaviors regulated by different neuroendocrine systems, these results could indicate that CBZ has a differential effect on fish behavioral stress response and cortisol levels, depending on the behavioral test used and stressor applied.