Publication Abstract

The effect of photoperiod on diel rhythms in serum melatonin, cortisol, glucose and electrolytes in the common dentex, Dentex dentex

The effect of photoperiod on dielrhythms in serum melatonin, cortisol, glucose and electrolytes in the common dentex, Dentex dentex

M. Pavlidis, L.N. Greenwood, M. Paalavuo, H. Molsa and T. Laitenen

Diel rhythms in serum concentrations ofmelatonin, cortisol, glucose, sodium, chloride, and potassium were studied in the commondentex, Dentex dentex, under different photoperiods (DD, 8L: 16D, 12L:12D, 16L:8D).Photoperiod affected both the diel rhythms and the absolute values of the estimated bloodcomponents. Regardless of the photoperiod, melatonin titers were elevated during thescotophase (384.3 ± 13.9 pg/ml) compared with a mean baseline level of 54.4 ± 2.7 pg/inlduring the photophase. Serum melatonin concentrations reflected the prevailing photoperiodand constantly elevated melatonin levels with no diel rhythmicity were evident in fishheld in the DD protocol. A circadian-like pattern in serum cortisol was observed in fishthat were kept at the DD and 8L:16D protocols with cortisol peak at 18:00 h in the night.Fish exposed to the 16L:8D regime showed highest cortisol levels at 10:00 h, while norhythmicity was evident under the 12L:12D protocol. A phase shift of 4 h between the peaksof cortisol and glucose was evident in fish exposed to the DD, 8L:16D, and 12L:12Dregimes. Diel patterns of changes in serum Na+ and C1- were observed only in the fish heldin the DD protocol. Serum K+ values were lowest during the first part of the scotophase under all regimes, except the16L:8D where no diel rhythmicity was detected. During the photophase, cortisol waspositively correlated with glucose, Na+, and Cl- and negatively with K+. During thescotophase, melatonin was positively correlated with glucose and electrolytes. Resultsindicated that cortisol may be responsible for the observed rhythmicity of glucose andthat melatonin may play a role in glucose and ion regulation in common dentex.

Reference:

M. Pavlidis, L.N. Greenwood, M. Paalavuo, H. Molsa and T. Laitenen, 1999. The effect ofphotoperiod on diel rhythms in serum melatonin, cortisol, glucose and electrolytes in thecommon dentex, Dentex dentex. General and Comparative Endocrinology, 113: 240-250.

M. Pavlidis, L.N. Greenwood*, M. Paalavuo, H. Molsa and T. Laitenen

General and Comparative Endocrinology, 113: 240-250