Influence of maturity status on the annual cycles of feeding and growth in Arctic charr reared at constant temperature

Temporal changes in feeding and growth of immature (1 +), maturing male (1 +), and mature male and female (3+) Arctic charr were studied by monitoring feed intake and growth of individually-marked fish for over 1 year. The fish were held at a constant temperature (4°C) under conditions of liberal feed supply. Feed intake and growth remained low in the period December-April, with only 20–60% of the fish having fed on each occasion that feed intake was monitored. Feed intake and growth increased markedly during the late spring and summer, but the increases were delayed by approximately 1–2 months in the immature fish compared with their maturing counterparts. Maturing fish decreased feeding during the late summer and by September there had been an almost complete cessation of feeding. This was reflected in changes in fish body weight and condition, both of which declined from August-September onwards. By contrast, the immature fish peaked in weight and condition in September, and weight loss during the autumn tended to be less rapid than observed for the maturing fish. The fish appeared to reduce feeding once a'threshold condition' of 1–4—1–5 had been attained. It is suggested that the fish may become anorexic once there has been replenishment of the energy reserves required for overwintering and, in the case of maturing individuals, for the completion of gonadal growth and Spawning.     

Melatonin implantation during spring and summer does not affect the seasonal rhythm of feeding in anadromous Arctic charr (Salvelinus alpinus)

Plasma melatonin levels in the high-latitude teleost Arctic charr (Salvelinus alpinus) are constantly low during summer when feeding activity is high, and high during the dark winter when they eat little and loose weight. The question arises if melatonin is involved in the phase-setting of annual rhythms of feeding and growth and if low summer melatonin production is permissive for high summer growth in this species. The present study was therefore set out to compare the seasonal appetite and growth rhythms in Arctic charr with constantly high plasma melatonin levels from February throughout the Arctic summer (melatonin implanted, average mid-day plasma melatonin levels 1,106 ± 147 pg/ml) with those of fish with natural plasma melatonin levels (vehicle implanted and untreated fish with average mid-day plasma melatonin levels of 94 ± 13 and 58 ± 6 pg/ml, respectively). Feed intake, body mass or body length, as well as the timing of the seasonal growth rhythm, were not affected by the high summer plasma melatonin level. Further, Arctic charr fasted for 3 months had a 24 h plasma profile of melatonin which was consistently higher throughout the scotophase compared to fed charr. Although the daily melatonin production seems to be affected by the energy status of the fish, melatonin does not seem to be directly involved in regulation of the seasonal feeding and growth rhythm in the high-latitude, anadromous Arctic charr.     

Sex steroids, growth and condition of Arctic charr broodstock during an annual cycle

Changes in plasma concentrations of sex steroids, growth rate and condition of repeat spawning (3+) male and female Arctic charr were studied throughout an annual reproductive cycle. Individually marked fish (mean weight approx. 500 g) were held under conditions of liberal food supply, constant temperature (4° C) and simulated natural photoperiod (Tromsø, 70° N). Once each month fish were weighed, measured and blood samples taken for steroid analysis. Plasma concentrations of testosterone (T), 11-ketotestosterone (11-KT) and oestradiol-17β (E₂) were determined using radioimmunoassay (RIA). Both male and female fish displayed distinct seasonal changes in plasma concentrations of sex steroids, growth rate and condition. From February (minimal concentrations) to March all sex steroids increased slightly and these elevated concentrations were maintained until May. Thereafter, there was a second, and far more pronounced, increase in plasma steroid concentrations which culminated in peak steroid concentrations in September–October. There was then a rapid decline during the spawning period. In winter, growth rate and condition were generally low, then increased during the spring, reached a peak during the summer, and then declined with the onset of autumn. During spring (March–May), the frequency distributions of plasma testosterone concentrations in both male and female fish were bimodal. The fish of the upper modal group of the distribution had significantly higher growth rates and condition than those in the lower modal group. In summer and early autumn (June–September) the association between T and growth rate changed. Significant negative correlations between T and growth rates were observed in females. There was an increase in endocrine activity, indicated by elevated plasma sex steroid concentrations in March, 7–8 months prior to maturation. It is suggested that this may be one factor influencing the onset of spring growth and energy deposition among maturing charr.     

Interaction between photoperiod and an endogenous seasonal factor in influencing the diel locomotor activity of the benthic polychaete Nereis virens Sars

The locomotor activity of Nereis virens Sars associated with food prospecting was investigated in response to photoperiod and season using an actograph. Experimental animals which had been reared under natural photoperiods were exposed to two constant photoperiodic treatments, LD 16:8 and LD 8:16, in both the autumn and winter and in the absence of tidal entrainment. Autocorrelation analysis of rhythmicity showed that during the autumn, animals under the LD 16:8 photoperiod displayed a strong nocturnal rhythm of activity, whereas animals under the LD 8:16 photoperiod showed only a weak nocturnal activity rhythm. This is believed to represent an autumn feeding cessation that is triggered when the animals pass through a critical photoperiod LD(crit) <12:>12. Later in the winter, however, animals exposed to both photoperiodic treatments showed strong rhythms of foraging activity irrespective of the imposed photoperiod. It is suggested that the autumn cessation may maximize the fitness of N. virens, a spring-breeding semelparous organism, by reducing risk during gamete maturation, while spontaneous resurgence of activity after the winter solstice permits animals that are not physiologically competent to spawn to accrue further metabolic reserves. This response is believed to be initiated by a seasonal (possibly circannual) endogenous oscillator or interval timer.     

The periodicity of primary increment formation in the otoliths of Arctic charr Salvelinus alpinus (L.)

The role of environmental factors in the regulation of sub-annual increment formation in fish otoliths appears to differ markedly between species. To examine the periodicity of primary increment formation in the otoliths of O + Arctic charr, Salvelinus alpinus (L.), and the effects of temperature, and photoperiod on their formation, fish were held under controlled environmental conditions. Primary growth increments were found in the otoliths of fish held at constant temperature (18° C) and at ambient temperature [fluctuating with a circadian and circannual rhythm (4–18° C)]. Consistent and significant disruptions in increment formation occurred however, in experimental groups subjected to rapid change from ambient photoperiod to a 6L: 6D photo-period for 96 h. Disruptions in increment formation were also observed immediately following transportation of fish between holding facilities and following disease treatment. The number of otolith increments formed in fish held on an ambient photoperiod regime, correlated closely with time elapsed in days since checkmark formation ( r = 0.989, P ≤0.001) in fish sampled sequentially over a period of 10 to 105 days. Thus we demonstrate that under conditions of ambient photoperiod, primary increments are formed daily.     

The influence of environmental manipulations on inter– and intra–individual variation in food acquisition and growth performance of Arctic charr, Salvelinus alpinus

Repeated measurements of food intake made on juvenile Arctic charr, Salvelinus alpinus , held under different rearing conditions enabled examination of the effects of environmental manipulations on both intra– and inter–individual variations in food intake to be made. This permitted the assessment of the influences of differential food acquisition on individual growth rates and biomass gain. When charr were held in isolation individual fish showed relatively little day–to–day variability in food intake and inter–individual differences in intake were small ('base–fine' values). All fish exhibited positive rates of growth and the overall range was narrow. Nevertheless, there was a highly significant positive correlation between food intake and growth, indicating that those individuals that consumed the greatest quantities of food were also those that had the highest rates of weight gain. The rearing of charr in groups led to increases in both intra– and inter–individual variations in food intake to levels considerably above 'base–line'. This increased variability in food intake was reflected in rates of weight gain being more variable amongst the charr reared in groups, with fish that lost weight often being recorded. Manipulation of the rearing environment had marked influences upon intra–individual variability in food intake, inter–individual differences in food acquisition and rates of weight gain. High stocking densities and exposure of the fish to moderate water currents were most effective in reducing levels of variability to approach those observed under 'base–line' conditions.     

Daily rhythms of clock gene expression and feeding behavior during the larval development in gilthead seabream,Sparus aurata

Light is the main environmental time cue which synchronizes daily rhythms and the molecular clock of vertebrates. Indeed, alterations in photoperiod have profound physiological effects in fish (e.g. reproduction and early development). In order to identify the changes in clock genes expression in gilthead seabream larvae during ontogeny, three different photoperiods were tested: a regular 12L:12D cycle (LD), a continuous light 24L:0D (LL) and a two-phases photoperiod (LL?+?LD) in which the photoperiod changed from LL to LD on day 15 after hatching (dph). Larvae were sampled on 10, 18, 30 and 60 days post-hatch (dph) during a 24?h cycle. In addition to the expression of clock genes (clock, bmal1, cry1 and per3), food intake was measured. Under LD photoperiod, larvae feed intake and clock genes expression showed a rhythmic pattern with a strong light synchronization, with the acrophases occurring at the same hour in all tested ages. Under LL photoperiod, the larvae also showed a rhythmic pattern but the acrophases occurred at different times depending on the age, although at the end of the experiment (60 dph) clock genes expression and feed intake rhythms were similar to those larvae exposed to LD photoperiod. Moreover, the expression levels of bmal1 and cry1 were much lower than in LD photoperiod. Under the LL?+?LD photoperiod, the 10 dph larvae showed the same patterns as LL treatment while 18 and 30 dph larvae showed the same patterns as LD treatment. These results revealed the presence of internal factors driving rhythmic physiological responses during larvae development under constant environmental conditions. The LL?+?LD treatment demonstrates the plasticity of the clock genes expression and the strong effect of light as synchronizer in developing fish larvae.     

Migration, growth and survival of wild and hatchery-reared anadromous Arctic charr (Salvelinus alpinus) in Finnmark, Northern Norway

Two groups of anadromous Arctic charr ( Salvelinus alpinus ) (size 200–350 mm) reared in heated water (6–12° C) under simulated natural photoperiod were individually tagged and released in spring 1988. The fish were released at two sites, in the estuary of the River Halselva and in the fjord, 2 km from the river mouth. Growth, timing of migration and survival of these hatchery-reared fish was compared to that of wild anadromous charr of the same size over a 4-year period. The hatchery-reared charr had poorer growth than the wild fish during their first year in sea water. They also resided longer in the sea and had a slightly lower survival than wild fish. During the second year, hatchery-reared charr displayed good growth, and after the third sea-season the fish were ready for slaughter at a size of approximately 800g. The results suggest that the successful development of Arctic charr ranching will be dependent upon production and release strategies that lead to improved migratory and feeding behaviour of the fish during their first season at sea.     

Synchronizing Effect of Photoperiod on the Dual Phasing of Demand-Feeding Rhythms in Sea Bass

Under natural environmental conditions, sea bass feeding rhythms are nocturnal in winter and diurnal the rest of the year. In this paper we describe the effect of contracting and expanding photoperiods and two skeleton photoperiods (SP) on the dual feeding rhythms of sea bass ( Dicentrarchus labrax L. ). To this end, twelve animals were held individually with access to self-feeders. First, the lights on and lights off were progressively delayed and advanced respectively by one hour in group 1 (G1), and conversely in group 2 (G2), so that the fish were exposed from a light/dark (LD) 12L:12D cycle to 2:22 LD (G1) and DL (G2) cycles and finally 0.25:23.75 LD (G1) and DL (G2). In the second experiment two SP's were used involving two light pulses separated by 12 hours, each pulse lasting 0.25 hours during the first two weeks and one hour during the succeeding two weeks. The results showed that diurnal and nocturnal sea bass tended to confine their feeding phase following the contraction of the LD cycle. Both SP's failed to simulate a complete photoperiod. In conclusion, the LD cycle appeared to drive the daily feeding rhythms but, the photoperiod length did not itself control the inversions of nocturnal and diurnal fish, so that other factors, in addition to photoperiod, may be involved in the control of the annual rhythms of phase inversions in sea bass.     

Metabolism and photoperiod in juvenile lake charr and walleye

Synopsis Basal and swimming oxygen consumption of juvenile lake charr (8 and 12°C and walleye (8°C) were measured for fish exposed either to a natural or constant photoperiod. Seasonal changes in oxygen consumption were not demonstrable at the basal level or for swimming at comparable speeds between 20 and 45 cm s^–1. The absence of a seasonal change in oxygen consumption among juvenile fish is in marked contrast to the seasonal pattern described in other studies at the basal and active level in mature fish.     

Growth and mortality of Arctic charr and European whitefish reared at low temperatures

This comparative study explores how low temperatures affect the mortality and growth of first generation hatchery-reared progeny of subarctic populations of Arctic charr (Salvelinus alpinus L.) and European whitefish (Coregonus lavaretus L.). Replicate fish groups where held under simulated natural light regimes (70°N) at three constant temperatures (1, 3 and 6°C). The mortality of Arctic charr was low (≤1.4%) at all temperature treatments, whereas the mortality of whitefish increased with decreasing temperature from 6% at 6°C to 33% at 1°C. The Arctic charr exhibited higher growth rates than whitefish at all three temperature regimes. All groups of Arctic charr increased in weight, whereas whitefish held at 1°C did not gain weight throughout the experimental period of 133 days. Arctic charr exhibited a large intraspecific variability in growth leading to large variations in size-structure, whereas whitefish in contrast showed very homogenous growth and size-structure patterns; a dissimilarity probably related to species-specific differences in antagonistic behaviour. Evidently, Arctic charr are more cold water adapted than whitefish and are able to maintain growth at extremely low temperatures. Arctic charr thus appear to be the most suitable species for aquaculture at low water temperatures.     

Physiological and social constraints on growth of Arctic charr, Salvelinus alpinus L.: an investigation of factors leading to stunting

When stunted (runt) Arctic charr, Salvelinus alpinus , were reared together in small groups growth rates were low. Contrary to expectation, there did not arise a rapidly growing despot within each group. It is suggested that the narrow size range offish within groups prevented the rapid formation of clear-cut dominance hierarchies. Fish reared in isolation had significantly higher and more variable rates of growth than those held in groups, demonstrating that social interactions between individuals were responsible for growth suppression of grouped-reared fish. There were no significant differences in growth rates between fish allowed visual contact with conspecifics and those held in visual isolation, indicating that visual contact is insufficient to cause growth depensation in Arctic charr. Despite the fact that growth rates of stunted (runt) Arctic charr improved when they were held in isolation, the growth rates recorded were substantially lower than those of normal individuals reared under hatchery conditions. It is concluded that physiological (genetic) factors are important in the determination of the slow growth rates of stunted (runt) Arctic charr and that this trend is exacerbated by social interactions with more rapidly growing siblings.     

Seawater tolerance in captive high-Arctic Svalbard charr (Salvelinus alpinus): effect of photoperiod and body size

Anadromous Arctic charr (Salvelinus alpinus) returning after spending summer at sea were captured in a fish trap in the Dieset River on Spitsbergen (79°10'N), Svalbard. Fish selected for breeding were transported to Trondheim in mainland Norway. Eggs obtained from the charr were fertilized and incubated in total darkness. First-fed alevins and resulting parr were kept under continuous light until an age of 0+ and 1+ years, respectively. Some 1+ charr were kept as controls under a continuous short-day photoperiod (6L:18D) from autumn until the end of the experiment the following July. Charr aged 0+ and 1+ years old were exposed to a short-day photoperiod from October until January and a simulated natural photoperiod for 80°N from January until the end of the experiments. Challenge tests demonstrated a size-dependent seawater tolerance for charr with a body length less than 18 cm. Fish smaller than 12 cm did not survive the 96-h test period. The larger charr kept under simulated natural photoperiod developed increased hypoosmoregulatory capacity. Charr kept under short-day treatment showed a slight, short-lived increase in seawater tolerance. A 7-days seawater challenge test at the end of the experiment (July) demonstrated that the anticipatory seawater preparation in charr is influenced by photoperiod. We conclude that offspring from anadromous high-Arctic charr must achieve a threshold body size (>25 cm) before they can respond to photoperiod signals which trigger the development of the hypoosmoregulatory capacity typical for smoltifying salmonids.     

Synchronizing Effect of Photoperiod on the Dual Phasing of Demand-Feeding Rhythms in Sea Bass

Under natural environmental conditions, sea bass feeding rhythms are nocturnal in winter and diurnal the rest of the year. In this paper we describe the effect of contracting and expanding photoperiods and two skeleton photoperiods (SP) on the dual feeding rhythms of sea bass (Dicentrarchus labrax L.). To this end, twelve animals were held individually with access to self-feeders. First, the lights on and lights off were progressively delayed and advanced respectively by one hour in group 1 (G1), and conversely in group 2 (G2), so that the fish were exposed from a light/dark (LD) 12L:12D cycle to 2:22 LD (G1) and DL (G2) cycles and finally 0.25:23.75 LD (G1) and DL (G2). In the second experiment two SP's were used involving two light pulses separated by 12 hours, each pulse lasting 0.25 hours during the first two weeks and one hour during the succeeding two weeks. The results showed that diurnal and nocturnal sea bass tended to confine their feeding phase following the contraction of the LD cycle. Both SP's failed to simulate a complete photoperiod. In conclusion, the LD cycle appeared to drive the daily feeding rhythms but, the photoperiod length did not itself control the inversions of nocturnal and diurnal fish, so that other factors, in addition to photoperiod, may be involved in the control of the annual rhythms of phase inversions in sea bass.     

The influence of previous feeding regime on the compensatory growth response of maturing and immature Arctic charr, Salvelinus alpinus

Alternating periods of food deprivation with those of unlimited provision of food depressed the growth of Arctic charr, Salvelinus alpinus , below that of controls. Fish that were deprived of food and then fed on alternate weeks (1:1) were larger than those that were exposed to periods of 1 5- or 3-week deprivation and feeding (1·5:1·5 or 3:3). On receiving excess food supplies following 24 weeks on the restricted feeding regimes the previously-restricted fish grew more rapidly than the controls. The greatest compensatory growth was displayed after the 3:3 regime, followed by the 1·5: 1·5 and then the 1:1 feeding regime. At the termination of the experiment there were no significant differences in body weight between fish fed according to the different regimes during the period that food restriction was imposed. Growth patterns of the immature males and females were similar, but mature males were significantly lighter than the immature fish by the end of the experiment. Both immature and maturing fish displayed a compensatory growth response on return to adequate feeding. Beginning food restriction in May did not influence the proportions of male fish ( c . 60%) which were mature in the autumn.     

Daily patterns of mRNA expression of two core circadian regulatory proteins, Clock2 and Per1, and two appetite-regulating peptides, OX and NPY, in goldfish (Carassius auratus)

The aim of this study was to examine the daily hypothalamic mRNA expression profiles for two core circadian regulatory proteins, CLOCK2 and PER1, and for two neuropeptides that regulate wakefulness and food intake, OX and NPY, in goldfish. The profiles were determined for fish at different nutritional states (i.e. fed or unfed on sampling day) and held at different photoperiods (i.e. 16L:8D photoperiod vs. constant light LL). Our results show that under a 16L:8D photoperiod, both fed and unfed goldfish exhibit clear antiphasic daily rhythms of hypothalamic Clock2 and Per1 mRNA expression levels, whereas under LL, daily Clock2 rhythms are seen in both fed and unfed fish while significant rhythms of Per1 mRNA expression only persist in unfed fish. In fish held under 16L:8D, but not under LL, there was significantly higher Per1 expression in fed fish at feeding time than in unfed fish. Daily variations in hypothalamic OX mRNA expression levels with peaks observed prior to both feeding time and the onset of darkness, were displayed under a 16L:8D photoperiod, whereas exposure to LL resulted in lower expression levels with no significant daily variations. Fish held under LL, but not under 16L:8D, showed significant daily variations in NPY mRNA expression with a peak prior to feeding time. Taken together, our results suggest that the mRNA expression of both appetite-regulating and circadian proteins display daily variations and that these patterns can be affected by external cues such as feeding and photoperiod.     

Regulation by Photoperiod of Seasonal Changes in Body Mass and Reproductive Function in Gray Mouse Lemurs (Microcebus murinus): Differential Responses by Sex

Microcebus murinus exhibits highly seasonal biological rhythms to cope with extreme seasonality in availability of resources. To study the role of daylength on seasonal changes in body mass and reproductive function, we exposed male and female gray mouse lemurs to natural, constant, or alternating light cycles for 2 years under constant environmental conditions. When exposed to either constant short (SD: 10 h light/day), long (LD: 14 h light/day), or intermediate (ID: 12 h light/day) daylength, males and females maintained a constant body mass with no spontaneous cyclic variation. We only observed typical seasonal body mass changes in subjects exposed to alternating periods of SD and LD, the weight gain being triggered by SD, whereas weight loss occurred under LD. Reproductive activity in females proceeded from an endogenous rhythm that was expressed under constant daylengths. In contrast, changes in reproductive activity in males depended on daylength variation. In both sexes, SD and LD have direct inhibitory or stimulatory effects on reproductive activity. In females, daylength regulates breeding season by synchronizing an endogenous sexual rhythm with the season, whereas in males, the perception of a critical photoperiod is used to determine the subsequent onset or arrest of their breeding season. These sexual differences in the effect of daylength could be related to sex-specific differences in reproductive constraints.     

Seasonal changes in some plasma hormones in pigeons from different environments

Seasonal variation in the plasma concentration of lutropin (LH), follitropin (FSH), prolactin (PRL), thyroxine (T4), triiodothyronine (T3) and corticosterone (B) were measured in the pigeon by RIA methods. Pigeons were maintained indoors under constant ambient temperature (Ta) and simulated natural daylight (LD), 12:12 L:D regimens or outdoors exposed to seasonal variations in temperature and photoperiod at Oulu, Finland. Only slight changes of gonadotropins (LH, FSH) were observed throughout the year, without any clear photosensitive or photorefractory period. In the indoor (natural LD) group, LH stayed elevated from May until October. Interdependence between the circannual hormonal fluctuation and photoperiod could not be shown, although the amplitude of FSH, T4 and T3 fluctuation of pigeons maintained in laboratory conditions were greater than that of natural LD and outdoor pigeons, whose circannual rhythms were similar. A high concentration of plasma PRL in autumn and the peak value of B in winter for all groups are thought to be correlated to lipid metabolism. Two peaks, the first in winter and the second in autumn, observed in T4 and T3 hormone profiles, may be due to molting of the pigeons.     

The size of lipid depots-a factor contributing to the control of food intake in Arctic charr,Salvelinus alpinus?

Food intake of Arctic charr was greatest in the fish with reduced lipid depots. It is suggested that appetite declines as lipid accumulates and energy reserves become repleted, such that energy reserves are then maintained close to some set-point.