Influence of Constant Light and Darkness, Light Intensity, and Light Spectrum on Plasma Melatonin Rhythms in Senegal Sole

Abstract

Light is the most important synchronizer of melatonin rhythms in fish. This paper studies the influence of the characteristics of light on plasma melatonin rhythms in sole. The results revealed that under long-term exposure to constant light conditions (LL or DD), the total 24 h melatonin production was significantly higher than under LD, but LL and DD conditions influenced the rhythms differently. Under LL, melatonin remained at around 224 pg/ml throughout the 24 h, while under DD a significant elevation (363.6 pg/ml) was observed around the subjective evening. Exposure to 1 h light pulses at MD (mid-dark) inhibited melatonin production depending on light intensity (3.3, 5.3, 10.3, and 51.9 microW/cm(2)). The light threshold required to reduce nocturnal plasma melatonin to ML (mid-light) values was 5.3 microW/cm(2). Melatonin inhibition by light also depended on the wavelength of the light pulses: while a deep red light (lambda>600 nm) failed to reduce plasma melatonin significantly, far violet light (lambda(max)=368 nm) decreased indoleamine's concentration to ML values. These results suggest that dim light at night (e.g., moonlight) may be perceived and hence affect melatonin rhythms, encouraging synchronization to the lunar cycle. On the other hand, deep red light does not seem to inhibit nocturnal melatonin production, and so it may be used safely during sampling at night.

The effects of continuous photoperiod (24L:0D) on growth of juvenile barramundi (Lates calcarifer)

“…Studies in Nile tilapia and African catfish demonstrated a much clearer suppression of melatonin levels under constant light; however, an endogenous rhythm was maintained for 18 and 4 days, respectively, for both species under constant darkness (Martinez-Chavez et al 2008). Similar to the current study, the persistence of reasonably high levels of melatonin production throughout the subjective night-time has been observed in Senegal sole (Solea senegalensis) maintained under constant light for a duration of 4 months (Oliveira et al 2007). However, in further experiments, acute light pulses (of various intensities and wavelengths) were able to reduce night-time melatonin levels in fish adapted to a 16L:8D cycle (Oliveira et al 2007).…”

“…Similar to the current study, the persistence of reasonably high levels of melatonin production throughout the subjective night-time has been observed in Senegal sole (Solea senegalensis) maintained under constant light for a duration of 4 months (Oliveira et al 2007). However, in further experiments, acute light pulses (of various intensities and wavelengths) were able to reduce night-time melatonin levels in fish adapted to a 16L:8D cycle (Oliveira et al 2007). It is possible that barramundi have developed a specific adaptation to the relatively stable tropical photoperiod environment which they experience under normal conditions, as suggested by Martinez-Chavez et al (2008) for other tropical species.…”

Influence of the lunar cycle on plasma melatonin, vitellogenin and sex steroids rhythms in Senegal sole, Solea senegalensis

“…Melatonin levels in plasma samples were measured by a Radioimunoassay commercial Kit (Melatonin Direct RIA, Biosource, Belgium), with a lower limit of quantification (LLOQ) of 2 pg/ml, as described by Oliveira et al, (2007).…”

Endocrine mechanisms mediating temperature-induced reproductive behavior in red-sided garter snakes (Thamnophis sirtalis parietalis)

“…All scotophasic blood samples were collected under dim red light, as this wavelength of light does not inhibit melatonin production (e.g. Benshoff et al, 1987;Oliveira et al, 2007).…”