Variations in plasma melatonin levels of the rainbow trout (Oncorhynchus mykiss) under various light and temperature conditions (original) (raw)
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Biological Rhythm Research, 2014
The daily profiles of melatonin and arylalkylamine N-acetyltransferase (AANAT) protein, the key enzyme of the melatoninergic pathway, in three anatomical segments of gut were studied in carp which were held under natural (NP) or long (LP; LD 16:08) or short (SP; LD 08:16) photoperiods or continuous light (LL; LD 24:00) or continuous darkness (DD; LD 00:24) for 30 days. The levels of melatonin and the density of a~23 kDa AANAT protein, in each gut segment, exhibited a daily rhythm with a peak at midday, irrespective of LD regimens to which the carp were held. None of the photo schedules had any significant effects on mesor values of gut melatonin and AANAT. However, compared to the rhythm features in NP fish, a significant reduction in the amplitude and a significant phase delay in the midday peak, as depicted by the value of acrophase (Ø), were noted in the gut of SP and DD carp. Collectively, it appears reasonable to argue that environmental lighting conditions may not be the synchronizer of daily periodicity in gut melatoninergic system, though the secondary effects of available light in determining its rhythm features in carp may not be ignored.
Biological Rhythm Research, 2014
A temporal relationship between the daily and seasonal profiles of melatonin (N-acetyl-5-methoxytryptamine) in three different parts of gut, pineal, and serum as well as the density of arylalkylamine N-acetyltransferase (AANAT) protein, the key regulator of melatoninergic pathway in the pineal and respective regions of gut has been sought in a tropical carp Catla catla under natural photo-thermal conditions. The tissue samples were collected at four different clock hours in a daily cycle and the same was repeated in four different seasons in an annual cycle. In a daily cycle, concentrations of melatonin as well as the band intensity of a $23 kDa AANAT protein in each segment of gut, irrespective of sampling months, exhibited a peak at midday, while both the variables in the pineal and melatonin in serum showed a peak either in late dark phase (in March) or at midnight (in the remaining seasons). The simple correlation coefficient analysis of values revealed a negative correlation between the melatoninergic system in the gut and the pineal. Notably, seasonal fluctuations of photoperiod as well as water temperature exhibited a negative correlation with the daily peak values of pineal and serum melatonin, but no significant correlation with the respective values of gut melatonin. In conclusion, attainment of a daily peak in melatonin in the gut, unlike in the pineal and serum, does not seem to be a dark-dependent phenomenon.
Journal of Experimental Biology, 2011
Melatonin has been suggested to play a role in fish osmoregulation, and in salmonids has been related to the timing of adaptive mechanisms during smolting. It has been described that acclimation to different environmental salinities alters levels of circulating melatonin in a number of fish species, including rainbow trout. However, nothing is known regarding salinity effects on melatonin synthesis in the pineal organ, which is the main source of rhythmically produced and secreted melatonin in blood. In the present study we have evaluated, in rainbow trout, the effects of acclimation to different salinities on day and night plasma melatonin values and pineal organ melatonin synthesis. Groups of freshwater (FW)-adapted rainbow trout were placed in tanks with four different levels of water salinity (FW, 6, 12, 18 p.p.t.; parts per thousand) and maintained for 6h or 5days. Melatonin content in plasma and pineal organs, as well as the pineal content of serotonin (5-HT) and its main oxidative metabolite (5hydroxyindole-3-acetic acid; 5-HIAA) were measured by high performance liquid chromatography. In addition, day-night changes in pineal organ arylalkylamine N-acetyltransferase (AANAT2) activity and aanat2 gene expression were studied. Plasma osmolalities were found to be higher in rainbow trout exposed to all salinity levels compared with the control FW groups. A salinity-dependent increase in melatonin content was found in both plasma and pineal organs. This effect was observed during the night, and was related to an increase in aanat2 mRNA abundance and AANAT2 enzyme activity, both of which also occurred during the day. Also, the levels of indoles (5-HT, 5-HIAA) in the pineal organ were negatively affected by increasing water salinity, which seems to be related to the higher recruitment of 5-HT as a substrate for the increased melatonin synthesis. A stimulatory effect of salinity on pineal aanat2 mRNA expression was also identified. These results indicate that increased external salinity promotes melatonin synthesis in the pineal organ of rainbow trout by enhancing synthesis of AANAT protein independently of its regulation by light. The possibility that pineal melatonin is a target for hormones involved in the response of fish to osmotic challenge is discussed, as well as the potential role of melatonin in the timing of osmoregulatory processes.
2011
A B S T R A C T n the present study, the melatonin levels were measured in pearl mullets (also known as Van fish) and trouts. Pearl mullets grow naturally in Lake Van in Turkey, and trouts, raised by private fish farms, were used as study materials. These fish are known to secrete melatonin, a hormone associated with development and stress, as occurs in human beings. Melatonin was measured in the plasma taken from living pearl mullets and trouts by an ELISA method using commercial kits. The study was conducted in accordance with the ELISA kit procedure. In the spring, the mean melatonin levels of trouts were 160.8 ± 4.090 pg/mL in light and 198.3 ± 3.694 pg/mL in dark, whereas in winter 86.69 ± 3.203 pg/mL and 128.9 ± 1.999 pg/mL in light and dark, respectively. In pearl mullets, the mean melatonin levels were 84.73 ± 2.281 pg/mL in light and 118.1 ± 2.560 pg/mL in dark in spring, and in winter 36.32 ± 1.627 pg/mL in light and 70.53 ± 2.919 pg/mL in darks (p < 0.001).The results ...
Aquaculture, 2013
Two studies were performed to study the effect of different light intensities on melatonin secretory profiles in Atlantic cod (Gadus morhua L.). In an indoor tank study, plasma melatonin profiles were measured over a 24-hour cycle in juvenile Atlantic cod reared under a 12 h light:12 h dark photoperiod, having either a high or low daytime light intensity (15.5 or 0.16 μE·cm −2 ·s −1 ). In a second study, plasma melatonin levels were measured in Atlantic cod kept in traps at three depths (4, 9 and 14 m) in a large sea cage following exposure to the following five experimental light regimes: (1) natural light (NL), (2) NL + artificial constant light (LL) at 2, 7 and 12 m depth, (3) NL + LL at 2 or 12 m, (4) NL + LL at 2 m and (5) NL + LL at 2 m together with additional surface shading. The vertical distribution of free swimming Atlantic cod in the same sea cage was monitored using hydroacoustics. In the tank experiment, diurnal plasma melatonin profiles were similar under low and high light intensity, remaining low during the light period, then increasing rapidly within 15-30 min of lights off, before peaking around midnight. In the sea cage experiment, fish under NL showed a similar diurnal rhythm in plasma melatonin levels, with high melatonin levels during the dark period, although at sunrise melatonin levels started to fall earlier in fish kept at 4 m depth compared to fish kept at 9 and 14 m. Overall, melatonin profiles were most effectively reduced, in terms of relative (day/night) plasma levels, in those fish sampled at the deepest depth (14 m). Relative plasma melatonin levels were correlated to the distance from the artificial light source and the intensity of the ambient light. Dispersed light (lamps at 2, 7 and 12 m) was the most effective light regime for inhibiting the nocturnal rise in plasma melatonin ratios in fish sampled at all three depths. Finally, exposure to the different light regimes did not influence the vertical distribution of Atlantic cod within the sea cage, which consistently remained close to the bottom of the cage.
Current knowledge on the melatonin system in teleost fish
2010
Melatonin is a much conserved feature in vertebrates that plays a central role in the entrainment of daily and annual physiological rhythms. Investigations aiming at understanding how melatonin mediates the effects of photoperiod on crucial functions and behaviors have been very active in the last decades, particularly in mammals. In fish a clear-cut picture is still missing.
2017
Annual variation of photoperiod is the most regular phenomenon that has strong predictive value in the temporal organization of seasonal activities in biological world, especially reproduction. The pineal organ, has the most important role in melatonin release under the different light condition. Melatonin is a much conserved feature in vertebrates that plays a central role in the entrainment of daily and annual physiological rhythms. The present study carried out in order to underestand different light intensity and photoperiod effects on melatonin release in whitespotted rabbitfish (siganus sutor) brood stock. For this purpose, 9 treatments, under artificial lighting conditions with 3 levels of photoperiod and light intensity include (16L/8D), (12L/12D), (6L/16D) and 1000, 2000, 3000 Lux, with a control treatment (natural light) on a period of 60 days studied. At the end of period analyzing the blood showed that the rate of melatonin in all of the male and female treatments in tre...
Daily variations in melatonin binding sites in the masu salmon brain
Neuroscience Letters, 2003
Daily variations in melatonin binding sites in the brain of underyearling masu salmon Oncorhynchus masou were examined by radioreceptor assay using 2-[ 125 I]iodomelatonin as the radioligand. Fish were reared under a natural photoperiod in July and sampled eight times at 3 h intervals from 12:00 to 09:00 h. Plasma melatonin levels showed robust daily rhythms in both precocious males and immature females, with high and low levels during night and day, respectively. The affinity (K d) and density (B max) of melatonin binding sites in the brain also showed similar variations. There were significant positive correlations between the plasma melatonin levels and the K d or the B max in immature females and between the K d and B max values in both precocious males and immature females. These results indicate that melatonin binding sites in the brain showed daily variations under a natural photoperiod in masu salmon.
Fish Physiology and Biochemistry, 2000
Reproduction in fish is cyclical and timed to guarantee the survival of the offspring. Seasonal variations in reproductive hormones of fish have been deeply investigated in fish over the last years. However, there are few studies regarding the daily changes in reproductive hormone profiles in teleosts. The aim of the present research was to investigate the effects of photoperiod manipulation on melatonin and reproductive hormones (pituitary sbGnRH, pituitary LH and plasma LH, testosterone [T], and 11-ketotestosterone [11KT]) daily rhythms in male sea bass, kept in net cages under farming conditions in winter (9L:15D). Fish were distributed in two groups, one under constant long photoperiod (18L:6D) and the other under natural photoperiod. The photoperiod strongly influenced the daily melatonin profile, so that the duration of the nocturnal melatonin rise was longer in the control group than in the group exposed to the artificial photoperiod (18L:6D). A daily rhythm was observed in the pituitary sbGnRH profile in both groups, showing the lowest levels during the dark period. A daily rhythm of pituitary LH was detected in the control group, which was suppressed in the group under long photoperiod. Daily variations in plasma LH were observed, the highest levels being found in the dark phase in both groups, although this profile was significantly altered by artificial light, maintaining a fixed relationship between the first nocturnal rise of melatonin and the nocturnal peaks of plasma LH in both groups. Plasma T levels showed significant fluctuations in their daily cycle following a sinusoidal pattern with an acrophase around sunrise in both groups, without any influence of light regime. No significant daily variations in plasma levels of 11-KT were observed in none of the groups. Our results provide the first evidence of the presence of daily variations in pituitary sbGnRH content, pituitary and plasma LH, and plasma T in sea bass. Artificial lights suppressed the circulating melatonin and significantly affected the daily rhythm of LH storage and release.