Early-Life Behavior Phenotypes and Cortisol Responses to Common Lab Stressors in a Cichlid Fish

The stress response is highly conserved across species, and increased glucocorticoid release (cortisol in fishes) is a key element. In the highly social cichlid fish, Burton’s Mouthbrooder ( Astatotilapia burtoni ), stress axis activity is associated with juvenile social behavior and status, and it mediates early-life social effects, yet little is known about early-life stress physiology. We measured water-borne cortisol, a non-invasive method, in juveniles less than 1-week old. We first tested whether juveniles habituate to the beaker confinement necessary for sample collection. Repeated exposure to a beaker did not affect cortisol compared to handled and unhandled controls. In a separate cohort, we next measured behavior in an open field exploration and social cue investigation, followed by a test of whether common lab stressors elevated cortisol. Controls were undisturbed in a collection beaker (90 min). For the stressor treatments, we collected three sequential samples (30 min each) to try and quantify stress response peak and recovery; however, we found no effect of time. Stressors included handling, brief net confinement, and brief gentle movement. These stressors led to a significant increase in cortisol, with the highest levels resulting from confinement. The behavior tests revealed a bold-shy axis across both tests, describing the behavior of most individuals. A distinct group of socially-motivated juveniles showed a dramatic switch, staying in the territory during the open field but leaving to investigate the social cue. We found no associations between behavior and cortisol response. This work provides insight into early-life behavior and stress axis development and function.