Seasonal and daily plasma melatonin rhythms and reproduction in Senegal sole kept under natural photoperiod and natural or controlled water temperature

Abstract

The melatonin daily rhythm provides the organism with photoperiod-related information and represents a mechanism to transduce information concerning time of day. In addition, the duration and amplitude of the nocturnal elevation gives information about duration and thus the time of year. In this study, we investigate the existence of an annual rhythm of plasma melatonin in the Senegal sole. Differences in plasma melatonin levels between fish kept at a controlled temperature (17-20 degrees C) and those exposed to the environmental temperature cycle (11.5-25 degrees C) were also examined throughout the year. Spawning was registered in both groups to determine the time of year in which reproductive rhythms occurred. Our results pointed to the existence of an annual rhythm of plasma melatonin at mid-darkness (MD), with the highest levels (203 +/- 44 pg/mL) observed when water temperature reached 25 degrees C. Water temperature influenced nocturnal, but not diurnal melatonin. Daily melatonin rhythms showed seasonal differences, with higher mean nocturnal levels during the summer solstice (138 +/- 19 pg/mL) and autumn equinox (149 +/- 49 pg/mL). When animals were kept at a constant temperature throughout the year, plasma melatonin levels differed from those observed in fish exposed to the environmental temperature cycle. Regarding the reproductive rhythms, spawning was observed at the end of spring in sole kept under natural temperature conditions, whereas no spawning at all was registered in sole reared at a constant temperature. In short, both photoperiod and temperature affected melatonin production in the Senegal sole, transducing seasonal information and controlling annual reproductive rhythms.

Daily oxygen consumption rhythms of Senegalese sole solea senegalensis (Kaup, 1858) juveniles

“…Senegalese sole appears to be strongly influenced by photoperiod; however daily metabolic rate rhythm, to our knowledge has not been reported. The data of the present study is in accordance with the idea that Senegalese sole is a nocturnal species, as clearly shown by spawning and melatonin rhythms (Bayarri et al, 2004;Oliveira et al, 2009;Vera et al, 2007).…”

Melatonin action in a midbrain vocal-acoustic network

“…In some fish species, it has been found that although the duration of a nocturnal rise in circulating melatonin levels is shortened in response to long day lengths, the amplitude of the rise is higher during the spring/summer breeding season and is positively correlated with water temperature (García-Allegue et al, 2001;Iigo and Aida, 1995;Vera et al, 2007). If this is also true for the midshipman, as males migrate from wintering in deeper, colder waters to shallow, warmer intertidal zones for breeding (see Bass, 1996), a higher nocturnal peak in melatonin levels could lead to increased vocal excitability at night.…”

Clock‐Controlled Endogenous Melatonin Rhythms in Nile Tilapia (Oreochromis niloticus niloticus) and African Catfish (Clarias gariepinus)

“…However, in vivo data on endogenous melatonin rhythms are clearly lacking in fish with only very few species studied (Randall et al 1995;Pavlidis et al 1999;Kazimi and Cahill 1999;Bayarri et al 2004b;Migaud et al 2006;Vera et al 2007;Oliveira et al 2007). A recent in vivo study performed on temperate fish species (sea bass, Atlantic salmon and Atlantic cod) has shown that when acclimatised to a 12L:12D photoperiod at two different temperatures (10 and 18 0 C) and thereafter exposed to DD, no circadian endogenous melatonin rhythm was maintained, with levels remaining as high as during night-time (Migaud et al unpublished).…”