Seasonal simulated photoperiods influence melatonin release and immune markers of pike perch Sander lucioperca

Abstract

Melatonin is considered as the time-keeping hormone acting on important physiological functions of teleosts. While the influence of melatonin on reproduction and development is well described, its potential role on immune functions has little been considered. In order to better define an immune modulation by the melatonin hormone, we hypothesized that natural variations of photoperiod and subsequent changes in melatonin release profile may act on immune status of pikeperch. Therefore, we investigated during 70 days the effects of two photoperiod regimes simulating the fall and spring in western Europe, on pikeperch physiological and immune responses. Samples were collected at 04:00 and 15:00 at days 1, 37 and 70. Growth, plasma melatonin levels, innate immune markers and expression of immune-relevant genes in head kidney tissue were assessed. While growth and stress level were not affected by the seasonal simulated photoperiods, nocturnal levels of plasma melatonin were photoperiod-dependent. Innate immune markers, including lysozyme, complement, peroxidase and phagocytic activities, were stimulated by the fall-simulated photoperiod and a significant correlation was made with plasma melatonin. In addition to bring the first evidence of changes in fish immunocompetence related to photoperiod, our results provide an additional indication supporting the immunomodulatory action of melatonin in teleosts.

Figure 1

Day-night (DP: dark phase; LP: light phase) variations of plasma cortisol (left) and glucose (right) in pikeperch juveniles exposed during 70 days to photoperiods simulating the fall or the spring in western Europe. Data are expressed as means ± SEM (n = 12). Capital letters indicate significant differences at p < 0.05. Stars (*) and (***) indicate main effects (day of sampling or time of the day) significant at p < 0.05 and 0.001, respectively.

Figure 2

Day-night (DP: dark phase; LP: light phase) variations of brain serotonergic (left) and dopaminergic (right) activities in pikeperch juveniles exposed during 70 days to photoperiods simulating the fall or the spring in western Europe. Data are expressed as means ± SEM (n = 12). Capital letters indicate significant differences at p < 0.05. Stars (*) indicate main effect (time of the day) significant at p < 0.05.

Figure 3

Day-night (DP: dark phase; LP: light phase) variations of plasma melatonin in pikeperch juveniles exposed during 70 days to photoperiods simulating the fall or the spring in western Europe. Data are expressed as means ± SEM (n = 9). Capital letters indicate significant differences at p < 0.05.

Figure 4

Day-night (DP: dark phase; LP: light phase) variations of (a) lysozyme, (b) peroxidase and (c) hemolytic complement activities in plasma and (d) phagocytic activity in spleen of pikeperch juveniles exposed during 70 days to photoperiods simulating the fall or the spring in western Europe. Data are expressed as means ± SEM (n = 15). Capital letters indicate significant differences at p < 0.05. Stars (***) indicate main effect (time of the day) significant at p < 0.001.

Figure 5

Day-night (DP: dark phase; LP: light phase) variations of (a) il-1, (b) hepc, (c) c3, (d) tnf-α and (e) lys gene expression in head kidney of pikeperch juveniles exposed during 70 days to photoperiods simulating the fall or the spring in western Europe. Data are expressed as means ± SEM (n = 12). Capital letters indicate significant differences at p < 0.05. Stars (*), (**) and (***) indicate main effects (day of sampling or time of the day) significant at p < 0.05, 0.01 and 0.001, respectively.