Effects of photoperiod and different intensities of light exposure on melatonin levels in the blood, pineal organ, and retina of the brook trout (Salvelinus fontinalis Mitchill)

Abstract

Daily variations in the melatonin concentration in the blood, pineal organ, and retina of the brook trout, Salvelinus fontinalis, were investigated in July under constant photoperiod (16 h L: 8 h D) and temperature (12 °C). Diel variations in melatonin levels in the blood and pineal organ showed similar patterns, with higher values during the night, whereas melatonin concentrations in the retina increased slightly in the first half of the light period. Light exposure of 1 h duration at mid-dark decreased melatonin levels in the blood and pineal organ in an intensity-dependent manner, whereas retinal melatonin levels increased with increasing light intensities. The minimum light intensity causing significant effects on the melatonin concentrations was 2 lx for the serum and 20 lx for the pineal organ and the retina. The parallelism between pineal and circulating melatonin patterns suggests that the lateral eyes of the trout have no significant endocrine function as far as the melatonin rhythm in the blood is concerned. Supporting evidence comes from the reversed response of retinal melatonin to light exposure at mid-dark, and from the low retinal melatonin concentrations found in this study. Thus, the serum melatonin rhythm of the brook trout seems to be mainly the result of rhythmic melatonin secretion from the pineal organ.

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“…Salmonids are found to have a passive response to the environmental LD signal where the elevated melatonin levels accurately reflect the length of the dark phase (Randall et al, 1995). As regards to plasma melatonin concentration measured in broodfish, our results were within the range previously reported in other fish: common carp (Cyprinus carpio), brook trout (Salvelinus fontinalis Mitchill), Atlantik salmon (Salmo salar) and common dentex (Dentex dentex) (Kezuka et al, 1988;Randal et al, 1995;Zachmann et al, 1992;Pavlidis et al, 1999). However, MLT implantation resulted in high levels of melatonin concentration in plasma during the scotophase period.…”

Diurnal variation in phagocytic activity of splenic phagocytes in freshwater teleost Channa punctatus: melatonin and its signaling mechanism

“…Concentration-dependent effect of melatonin The physiological concentration of plasma melatonin in teleost ranges from 400 pg/ml K1 ng/ml (Kezuka et al 1988, Zachmann et al 1992, Randall et al 1995. Therefore, phagocytes were incubated with varying concentrations of melatonin i.e.…”

Ocular Melatonin Rhythms in Teleost Fish

“…In the pike, goldfish, freshwater minnow, bigscaled redfin, honbera wrasse, and seagrass rabbitfish, ocular melatonin levels exhibit daily rhythms with higher levels during the dark phase [Falcón and Collin, 1991;Iigo et al, 1997a, b, e;Rahman et al, 2004]. However, in the rainbow trout, brook trout, and European sea bass, reversed melatonin profiles (with higher melatonin levels during the light phase than during the dark phase) have been reported [Gern et al, 1978;Zachmann et al, 1992;Iigo et al, 1997d;Sánchez-Vázquez et al, 1997;Zaunreiter et al, 1998;Garcia-Allegue et al, 2001]. Furthermore, acute light exposure during the dark phase increased ocular melatonin levels in the European sea bass [Iigo et al, 1997d].…”

“…Ocular melatonin rhythms in vivo have been reported only in a small number of species such as the rainbow trout Oncorhynchus mykiss , brook trout Salvelinus fontinalis , pike Esox lucius , goldfish Carassius auratus , freshwater minnow (oikawa) Zacco platyps , big-scaled redfin Tribolodon hakonensis , European seabass Dicentrarchus labrax , honbera wrasse Halichoeres tenuispinis , and seagrass rabbitfish Siganus canaliculatus [Gern et al, 1978;Falcón and Collin, 1991;Zachmann et al, 1992;Iigo et al, 1997a, b, d, e;Sánchez-Vázquez et al, 1997;Zaunreiter et al, 1998;Garcia-Allegue et al, 2001;Rahman et al, 2004]. In the pike, goldfish, freshwater minnow, bigscaled redfin, honbera wrasse, and seagrass rabbitfish, ocular melatonin levels exhibit daily rhythms with higher levels during the dark phase [Falcón and Collin, 1991;Iigo et al, 1997a, b, e;Rahman et al, 2004].…”