Influence of the light spectrum on the daily rhythms of stress and humoral innate immune markers in pikeperch Sander lucioperca

This study investigated the daily variations of stress markers namely plasma cortisol and glucose and some humoral innate immune markers, including peroxidase, lysozyme and complement activities, of pikeperch (Sander lucioperca) and the effect of light spectrum on these variations. Fish were reared under a white or red light spectrum at a constant photoperiod (12D:12 L). Samples were collected at 22:00, 04:00, 10:00 and 16:00 at days 1 and 42 of the experiment. After 42 days, the use of a red light spectrum led to a significant increase in final bodyweight. Specific growth rate reached 2.1 ± 0.18 and 1.8 ± 0.17% d⁻¹ under red and white spectra respectively. The profiles of plasma cortisol followed a cyclic activity with a surge during photophase at 10:00 without any effect of the light spectrum at day 42. Both lysozyme and peroxidase activities in blood followed a day-night variation with a peak at 4:00 corresponding to low cortisol values. No rhythmicity was detected for the complement activity but higher values were observed at 16:00 when cortisol values were lowest. Light spectra also influenced humoral immune markers with an increase in lysozyme activity and a decrease in peroxidase activity in a red light environment. The present results indicate a strong effect of the light environment, including the light-dark cycle and the light spectrum, on pikeperch physiology. Especially, some innate immune status seemed stimulated during the dark phase in relation to a decrease in the stress level markers. Such parallelism in the relationship between the immune status and stress markers may be affected positively or negatively by the light characteristics. Humoral immune markers were also modulated according to the light spectrum without no clear trend (stimulation or inhibition) for the immunocompetence status.