Circadian pattern of hepatosomatic index, liver glycogen and lipid content, plasma non-esterified fatty acid, glucose, T3, T4, growth hormone and cortisol concentrations in Oncorhynchus mykiss held under different photoperiod regimes and fed using demand-feeders

Abstract

The circadian patterns of several tissue and plasma metabolites, and several plasma hormone concentrations are described in rainbow trout (Oncorhynchus mykiss) that were held in groups under three different photoperiod regimes, and given free access to a demand-feeder. Regardless of photoperiod regime, all the measured parameters showed significant diel rhythms that appeared to be synchronized by dawn; dawn was represented by the concomitant onset of both light and feeding. The diel increases in hepatic glycogen content, and plasma T4 and cortisol concentrations were in phase with the main period of feeding activity, whereas the peaks in plasma T3 and glucose concentrations that may also be triggered by feeding activity, were delayed by several hours. The peaks in hepatosomatic index, plasma non-esterified fatty acids and plasma growth hormone concentrations were 180° out of phase with the main period of feeding activity, and associated with periods of hypophagia and low activity.

Glucosensing capacity in liver of rainbow trout displays day-night variations possibly related to melatonin action

“…Several parameters assessed in controls (for instance, GK activity in liver or PK activity in hypothalamus and hindbrain) displayed clear day-night differences, which in some cases agree with those described for the same species in the literature (Boujard and Leatherland, 1992;Reddy and Leatherland, 1994;Polakof et al, 2007c;Polakof et al, 2007d), allowing us to postulate the existence of daily rhythms. Treatment with glucose during the day induced hyperglycemia, which is in agreement with similar studies carried out previously in the same fish species (Polakof et al, 2007a;CondeSieira et al, 2010a).…”

Stress inhibition of melatonin synthesis in the pineal organ of rainbow trout (Oncorhynchus mykiss) is mediated by cortisol.

“…Those fish reared under normal housing conditions showed significant (experiment 1) or apparent (experiment 2) day-night variations of plasma cortisol with night values being higher than those measured during the day, in agreement with previous studies in the same species (Rance et al, 1982;Boujard and Leatherland, 1992) and others such as the brown trout (Pickering and Pottinger, 1983) and tilapia (Martínez-Chavez et al, 2008;Nikaido et al, 2010). Our results show that cortisol levels were higher in those acutely stressed groups (hypoxia and chasing), whereas they were lower in the high-density group in particular during the night.…”

“…For rainbow trout, many studies have reported increased plasma cortisol at night, peaking before the light onset, then falling and remaining low during the day (Rance et al, 1982;Boujard and Leatherland, 1992). Such a daily profile is also influenced by feeding time (Boujard and Leatherland, 1992), and supports rhythmic cortisol secretion being synchronized by both photoperiod and feeding activity, with differences among seasons.…”

“…Plasma cortisol levels display a circadian rhythm in teleost species such as common dentex, Dentex dentex (Pavlidis et al, 1999), but such daily pattern appears to depend on the fish species (Garcia and Meier, 1973;Pickering and Pottinger, 1983;Pavlidis et al, 1999;Saito et al, 2004;Ebbesson et al, 2008). For rainbow trout, many studies have reported increased plasma cortisol at night, peaking before the light onset, then falling and remaining low during the day (Rance et al, 1982;Boujard and Leatherland, 1992). Such a daily profile is also influenced by feeding time (Boujard and Leatherland, 1992), and supports rhythmic cortisol secretion being synchronized by both photoperiod and feeding activity, with differences among seasons.…”

“…Our results from cultured pineal organs support this hypothesis. In fish, plasma cortisol levels are known to cycle diurnally (Holloway et al, 1994;Reddy and Leatherland, 1995) and to change through the seasons (McLeese et al, 1994), although the cortisol profile exhibits speciesspecific daily and seasonal patterns affected by several factors such as photoperiod (Pickering and Pottinger, 1983) or feeding time (Boujard and Leatherland, 1992), among others. In some species, for example common dentex, daily fluctuations of plasma cortisol levels show endogenous rhythmic characteristics (Pavlidis et al, 1999).…”