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Sea bass change their feeding rhythms from diurnal to nocturnal in winter, returning to diurnal feeding in spring. Despite behavioral data, the physiological changes that take place during such changes remain unexplored. In this paper, blood glucose rhythms of European sea bass with diurnal/nocturnal self-feeding rhythms were investigated during phase inversions of their feeding behavior (in winter and spring) when both diurnal and nocturnal fish coexist. Blood glucose showed daily variations in both seasons (ANOVA, p&nbsp

Daily light and feeding cycles act as powerful synchronizers of circadian rhythmicity. Ultimately, these external cues entrain the expression of clock genes, which generate daily rhythmic behavioral and physiological responses in vertebrates. In the present study, we investigated clock genes in a marine teleost (gilthead sea bream). Partial cDNA sequences of key elements from both positive (Bmal1, Clock) and negative (Per2, Cry1) regulatory loops were cloned before studying how feeding time affects the daily rhythms of locomotor activity and clock gene expression in the central (brain) and peripheral (liver) oscillators. To this end, all fish were kept under a light-dark (LD) cycle and were divided into three experimental groups, depending on the time of their daily meal: mid-light (ML), mid-darkness (MD), or at random (RD) times. Finally, the existence of circadian control on gene expression was investigated in the absence of external cues (DD + RD). The behavioral results showed that seabream fed at ML or RD displayed a diurnal activity pattern (>91% of activity during the day), whereas fish fed at MD were nocturnal (89% of activity during the night). Moreover, seabream subjected to regular feeding cycles (ML and MD groups) showed food-anticipatory activity (FAA). Regardless of the mealtime, the daily rhythm of clock gene expression in the brain peaked close to the light-dark transition in the case of Bmal1 and Clock, and at the beginning of the light phase in the case of Per2 and Cry1, showing the existence of phase delay between the positive and negative elements of the molecular clock. In the liver, however, the acrophases of the daily rhythms differed depending on the feeding regime: the maximum expression of Bmal1 and Clock in the ML and RD groups was in antiphase to the expression pattern observed in the fish fed at MD. Under constant conditions (DD + RD), Per2 and Cry1 showed circadian rhythmicity in the brain, whereas Bmal1, Clock, and Per2 did in the liver. Our results indicate that the seabream clock gene expression is endogenously controlled and in liver it is strongly entrained by food signals, rather than by the LD cycle, and that scheduled feeding can shift the phase of the daily rhythm of clock gene expression in a peripheral organ (liver) without changing the phase of these rhythms in a central oscillator (brain), suggesting uncoupling of the light-entrainable oscillator (LEO) from the food-entrainable oscillator (FEO). These findings provide the basis and new tools for improving our knowledge of the circadian system and entraining pathways of this fish species, which is of great interest for the Mediterranean aquaculture.

Biological rhythms are driven by circadian oscillators, which are ultimately controlled by the cyclic expression of clock genes. Cryptochromes (CRY), blue light photoreceptors, belong to the negative elements of the transcriptional feedback loop into the molecular clock. This paper describes the cloning and characterization of two cryptochromes (cry1 and 2) in European seabass, which is considered an interesting chronobiology model due to its dual (diurnal/nocturnal) behavior. The cloned cDNA fragments encoded for two proteins of 567 and 668 amino acids, which included the FAD-binding and the DNA-photolyase domains. Moreover, both proteins had a high homology with cryptochrome proteins (Cry) of other teleost fish. These cry1 and 2 genes were expressed in several tissues of seabass (brain, liver, heart, retina, muscle, spleen, gill and intestine). In addition, the daily expression of cry1 was rhythmic in brain, heart and liver with the acrophase around ZT 03:15 h (after the onset of lights). Similarly, the cry2 daily expression was rhythmic in liver, peaking at ZT 03:28 h, whereas in brain the acrophase was at ZT 11:08 h (shortly prior to the offset of lights). These findings provide new elements to help understanding the functioning of the molecular clock of seabass.

Seabass is a fish species with dual (diurnal/nocturnal) feeding behavior, although little is known about changes in its molecular clock, physiology and metabolism linked to this dual behavior. In the research described here possible differences in clock gene expression in central (brain) and peripheral (liver) oscillators, and in physiology (blood glucose and amylase activity in mid-intestine) were studied in seabass with diurnal or nocturnal self-feeding patterns under LD 12:12 h (light:dark) (lights on = Zeitgeber Time (ZT) 00:00 h). The results revealed that per1 expression in brain shows daily rhythmicity with the acrophase (Φ) around the lights offset (ZT 12:00 h, Cosinor, p < 0.01) in both diurnal and nocturnal seabass. In liver, per 1 daily levels of expression were higher in diurnal fish (univariate GML, p < 0.02). Daily blood glucose variations were observed in both groups (ANOVA I, p < 0.01), with higher glucose levels occurring at night in nocturnal as well as in diurnal fish, although only diurnal seabass displayed a significant daily rhythm (Φ = ZT 16:52 h, Cosinor, p < 0.02). The highest values of amylase activity coincided with the feeding-phase of fish; that is, in nocturnal seabass the maximum was reached at ZT 18:00 h (ANOVA I, p < 0.01), whereas in diurnal seabass the Φ was ZT 03:39 h (Cosinor, p < 0.02). In short, our findings indicated that the feeding rhythm (diurnal vs. nocturnal) strongly influenced the daily patterns of digestive function and clock gene expression in the liver (feeding-entrained clock), but not in the brain (light-entrained clock).

It is widely held that the development of the circadian system during embryogenesis is important for future survival of an organism. Work in teleosts has been, to date, limited to zebrafish, which provides little insight into the diversity of this system within such a large vertebrate class. In this study, we analyzed the diel expression of per1, clock, and aanat2 in unfertilized rainbow trout oocytes and embryos maintained under either a 12:12 light:dark (LD) cycle or continuous illumination (LL) from fertilization. 24-h profiles in expression were measured at fertilization as well as 8, 21 42, and 57 days postfertilization (dpf). Both per1 and clock were expressed in unfertilized oocytes and all embryonic stages, while aanat2 expression was only measureable from 8 dpf. A reduction in both per1 and clock mean expression level between unfertilized oocytes/0-1dpf embryos and 8-9dpf embryos was suggestive of a transition from maternal RNA to endogenous mRNA expression. While aanat2 expression was not clearly associated with photic conditions, photoperiod treatment did alter the expression of per1 and clock expression/rhythmicity from as early as 8 dpf (per1), which could suggest the presence and functionality of an as yet unidentified “photoreceptor”. As a whole, this work demonstrates that clock systems are present and functional during embryonic development in rainbow trout. Further studies of their expression and regulation will help understand how the environment interacts with embryonic development in the species.

Behavioral rhythms of the Nile tilapia were investigated to better characterize its circadian system. To do so, the locomotor activity patterns of both male and female tilapia reared under a 12:12 h light-dark (LD) cycle were studied, as well as in males the existence of endogenous rhythmicity under free-running conditions (DD and 45 min LD pulses). When exposed to an LD cycle, the daily pattern of activity differed between individuals: some fish were diurnal, some nocturnal, and a few displayed an arrhythmic pattern. This variability would be typical of the plastic circadian system of fish. Moreover, reproductive events clearly affected the behavioral rhythms of female tilapia, a mouth-brooder teleost species. Under DD, 50% (6 of 12) of male fish showed circadian rhythms with an average period (t) of 24.1+0.2 h, whereas under the 45 min LD pulses, 58% (7 of 12) of the fish exhibited free-running activity rhythms with an average t of 23.9+0.5 h. However, interestingly in this case, activity was always confined to the dark phase. Furthermore, when the LD cycle was reversed, a third of the fish showed gradual desynchronization to the new phase, taking 7–10 days to be completely re-entrained. Taken together, these results suggest the existence of an endogenous circadian oscillator that controls the expression of locomotor activity rhythms in the Nile tilapia, although its anatomical localization remains unknown.

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 µW/cm2). The light threshold required to reduce nocturnal plasma melatonin to ML (mid‐light) values was 5.3 µW/cm2. Melatonin inhibition by light also depended on the wavelength of the light pulses: while a deep red light (λ>600 nm) failed to reduce plasma melatonin significantly, far violet light (λmax=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.Read More: http://informahealthcare.com/doi/abs/10.1080/07420520701534657

The daily locomotor and melatonin rhythms of the Senegal sole, a benthonic species of increasing interest in aquaculture, are still unknown, despite the fact that such knowledge is of prime importance for optimising its production. The aim of the present research was therefore to investigate the daily rhythms of locomotor activity and melatonin in the Senegal sole. For this purpose, the individual locomotor activity rhythms of fish were registered using a photocell. Plasma and ocular melatonin rhythms were studied in animals reared in circular tanks placed in earth under an LD 12:12 light regime and 16-18 °C temperature range (spring equinox). Blood and eye samples were taken every 3 h during a complete 24-h cycle. The impact of a light pulse in the middle of the dark period (MD) on plasma melatonin was also studied. Locomotor activity was mainly nocturnal, with 84.3% of the total activity occurring during darkness. The levels of plasma melatonin were higher at night (55 pg/ml) than during the day (2 pg/ml), while ocular melatonin levels appeared to be arrhythmic. Both weight and melatonin content were found to be significantly higher in the left eye in relation to the right eye. A light pulse in MD provoked a significant decrease in plasma melatonin levels. In summary, photoperiod is a key factor in synchronising locomotor activity and melatonin rhythms in the Senegal sole, whose nocturnal habits should be taken into account for their rearing by aquaculture.

Biology of European Seabass presents up-to-date reviews on key topics of seabass biology, written by leading scientific experts with extensive knowledge of seabass as well as their respective field of expertise. The book covers the biology and ecology of the different sea basses and the latest findings in molecular biology, physiology, and beh; International audience; The pineal gland of vertebrates is important because it produces and releases the time-keeping hormone melatonin (Klein et al. 1981). In most species investigated, the rhythm in melatonin production results from the activity of circadian clocks synchronized by photoperiod. However, the mechanisms through which this is achieved have been profoundly modified in the course of vertebrate evolution (Collin 1971, Collin and Oksche 1981). In aquatic species, cone-like photoreceptor cells concentrate a photoreceptive unit, clock machinery and melatonin-producing unit (Falcón et al. 2007a, 2010).

Biology of European Seabass presents up-to-date reviews on key topics of seabass biology, written by leading scientific experts with extensive knowledge of seabass as well as their respective field of expertise. The book covers the biology and ecology of the different sea basses and the latest findings in molecular biology, physiology, and beh; International audience; Marine fish larval culture is one of the main bottlenecks in the aquaculture industry. At hatching, most of the organs of marine fish larvae are not fully developed, and developmental processes initiated during embryogenesis continue during larval development in order to ensure the proper ontogenesis of organs and associated physiological functions, essential for the survival of individuals. Consequently, during the first weeks of life, marine fish larvae undergo significant morphological and physiological modifications to acquire all the adult features by the end of the larval period. This phase is certainly the most critical in the life cycle of fish, not only in natural environments, but also under controlled conditions. In aquaculture, in spite of the many advances made to control environmental cues, this stage of production can still suffer from substantial mortality impaired larval quality, influencing the overall performance of the rearing production, whose final objective is the obtention of enough fry of good quantity and quality for on-growing purposes.