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Most circadian rhythms are under the control of a major pacemaker located in the hypothalamic suprachiasmatic nucleus. Some of these rhythms, called marker rhythms, serve to characterize the timing of the internal temporal order. A marker rhythm, (e.g., one used in chronotherapy) has to be periodic and easy to measure over long periods using non-invasive methods. The most frequent reference variables for human chronotherapy include salivary melatonin or cortisol, urinary 6-sulfatoximelatonin, actimetry and core body temperature (CBT). Recent evidence suggests that sleepiness may be more closely linked to increased peripheral skin temperature than to a core temperature drop, and that distal skin temperature seems to be correlated and phase-advanced with respect to CBT, suggesting that heat loss from the extremities may drive the circadian CBT rhythm. The aim of the present study was to evaluate whether the wrist skin temperature rhythm could be used as a possible index of the human circadian system. To this end, wrist skin temperature (WT1), as determined by a wireless data logger in healthy normal living subjects, was correlated with sleep-wake diaries and oral temperature (OT) recordings. WT and sleep habits were studied in 99 university students. Each subject wore a wireless iButton sensor attached to the inner side of a sport wristband. Our results show that the WT rhythm exhibits an inverse phase relationship with OT, and it is phase-advanced by 60 min with respect to OT. WT started to increase in association to bed time and dropped sharply after awakening. A secondary WT increase, independent of feeding, was observed in the early afternoon. In conclusion, WT wireless recording can be considered a reliable procedure to evaluate circadian rhythmicity, and an index to establish and follow the effects of chronotherapy in normal living subjects.

The use of a single diet with a well defined composition to feed fish throughout their life cycle is an oversimplification that probably does not respond to their metabolic requirements. For example, the seasonal reproduction that characterizes most fish species demands changes in nutritional requirements. Bearing this in mind, the macronutrient selection pattern was studied from January to August in twelve individually housed sea bass exposed to a constant photoperiod (12L:12D h) and temperature (23+/-0.5 degrees C). The endogenous "seasonal" effect on food and energy intake regulation and macronutrient selection was determined, using protein (P), carbohydrate (CH), and fat (F) packaged separately into gelatine capsules, a method that prevents the diet chemosensory properties at oropharyngeal level from interfering with macronutrient selection. Energy intake changed monthly, the highest values being recorded in May and June and the lowest values in March and April. The preliminary results illustrated "seasonal" changes in the sea bass macronutrient selection pattern with, which showed a predominantly proteinic selection during April (53% P, 21% CH, 25% F) and lipidic in July (35% P, 19% CH, 42% F); the increase in fat selection from May to July being statistically significant. This is the first evidence supporting the existence of an endogenous rhythm in the "seasonal" energy regulation and macronutrient selection in fish through post-ingestive mechanisms and probably involving chemosensory detection in the gut and/or post-absorptive mechanisms, although the exact mechanisms involved have yet to be clarified.

Teleost fish are able to adjust their energy intake when fed on pure macronutrient sources, although the exact mechanisms regulating macronutrient selection remain unknown. Since cholecystokinin (CCK) has been reported to modify macronutrient selection patterns in mammals, we explored the effect of CCK administered orally to European sea bass on the selection of separately encapsulated macronutrients. CCK doses of 0.05, 0.15 and 0.25 mg/kg BW administered in gelatine capsules for 5 consecutive days produced a significant inhibition of total food intake (21, 28 and 51%, respectively) at highest doses, evenly reducing the quantity of all the macronutrients ingested and, without affecting their relative proportions in the diet. Oral administration of proglumide, a non-specific CCK receptor antagonist, at doses of 5, 15 and 25 mg/kg BW, induced a quantitative total food intake increase of 2, 18 and 44%, respectively, and an increase of 52% in CH and 43% in P quantity ingested at highest dose. Co-administration of proglumide (25 mg/kg BW) and CCK (0.25 mg/kg BW) in a single preload capsule blocked the effects observed with CCK alone. In conclusion, orally administered CCK induced an anorexigenic effect on both total food and single macronutrient intake, an effect that is counteracted by the CCK antagonist proglumide.

Sharpsnout seabream fed pure macronutrient capsules were challenged to fat dilution and fat deprivation in order to investigate the effects of fat level on energy intake regulation and macronutrient selection by fish, as they lack oropharyngeal chemosensory information from the diet. During the control phase, the fish were fed three individually encapsulated macronutrients, from which they composed a diet containing 67.36% protein (P), 19.08% carbohydrates (CH) and 13.57% fat (F), in terms of macronutrient weight intake percentage. During the second phase of the experiment, a lipid content reduction in F capsules from 55.0% to 13.4% did not significantly modify this selection pattern, energy ingestion or the number of capsules ingested of each macronutrient. During the third phase, in which they were subjected to fat deprivation, starting on almost the first day, the fish increased their total energy intake and total ingested number of capsules. These results reveal that fish are capable of distinguishing and selecting each of the three macronutrients contained in gelatine capsules, and that fish selection of a balanced diet from pure macronutrients is remarkably stable. Fish are capable of sustaining their macronutrient selection pattern and energy intake with very low amounts of fat in their diets (Phase 2). A certain instability in the initial P, CH and energy intake was only observed when fat was totally deprived (Phase 3), which resulted in higher values than those observed in Phase 1. In order to examine any possible effects of diet encapsulation, digestibility assays were performed in a second experiment. The fish were divided into two experimental groups and fed the same complete commercial diet, the only difference being the way it was presented to each group (pelleted or encapsulated). No statistical differences between the experimental groups were found with regards to both apparent digestibility coefficients and fish growth.

The existence of food anticipatory activity (FAA) in animals subjected to daily feeding schedules seems to be mediated by a feeding-entrainable oscillator (FEO). Such an FEO may help in anticipating meal time and so optimizing food acquisition and nutrient utilization. In this study we investigated the existence of FAA and whether digestive enzymes, plasma cortisol, hypothalamic NPY and gastrointestinal tract (GIT) and plasma melatonin were entrained by periodic feeding in goldfish. We observed that periodically fed goldfish showed FAA in locomotor activity as well as in amylase and NPY. Alkaline protease and GIT melatonin were higher after feeding, whereas plasma cortisol levels were reduced. Plasma melatonin remained unmodified before and after meal time. These results suggested that scheduled feeding entrained both behavioral and certain physiological patterns in goldfish, FAA being of adaptive value to anticipate a meal and prepare the digestive physiology of fish.

The sea bass is a teleost that is able to regulate its energy intake by selecting from pure macronutrient sources, although the regulatory mechanisms involved in this selection are unknown. Nutrient preloads are known to reduce food intake and modify macronutrient selection patterns in mammals, but no information is available on its effects in fish. The aim of the present work was to determine the effect of orally administered macronutrient preloads of protein (P), fat (F) or carbohydrate (CH) on the subsequent macronutrient selection, using for the purpose feed consisting of CH, P or F packaged separately in gelatin capsules. The macronutrient preloads left the total food intake unaltered, but caused differential changes in the pattern of macronutrient selection. The CH preload increased the selection of CH (39%) and decreased that of P (20%), independently of the fish's previous nutritional preferences. The F preload induced an F increase (32%) and a P decrease (18%) in P-preferring fish, but not in F-preferring fish in which the macronutrient selection pattern remained unaffected. The P preload stimulated F selection by 42% in P-preferring fish, but left the macronutrient selection pattern unchanged in F-preferring fish. In conclusion, oral macronutrient preloads affected the pattern of macronutrient selection in fish, acting by post-ingestive mechanisms. The effect was influenced by the fish's previous nutritional preference and/or status, which could depend on its metabolic capacity.

Sharpsnout seabream ability for macronutrient self-selection was studied using gelatine capsules containing pure macronutrients. In particular, the existence of non-oropharyngeal chemosensory pathways involved on protein (P), fat (F) and carbohydrate (CH) selection, as well as sharpsnout seabream response to dietary protein dilution were investigated. In a sequence of experimental phases, sharpsnout seabream were fed a pelleted complete diet, an encapsulated complete diet or a combination of separately encapsulated pure macronutrients. In order to induce associative learning, capsules containing a given macronutrient were paired with a particular colour. The animals composed a diet containing 62.7% P, 21.3% CH and 16.0% F, in terms of macronutrient percentage intake, and this selection pattern was maintained throughout all experimental phases. In a second experiment, individually kept sharpsnout seabream were challenged with protein dilution. After protein capsules were diluted (from 91.9% P to 56.3% P) with cellulose, the animals increased their protein intake to compensate for dilution in such a way that their energy intake was not significantly modified (17.4 kJ/100 g BW vs. 17.6 kJ/100 g BW after dilution). These results show that sharpsnout seabream feeding on encapsulated diets are able to select and maintain a particular diet composition, as well as sustain their energy intake, without using the diet's oropharyngeal chemosensory properties. Moreover, they were also able to maintain their protein intake after dilution, which highlights the importance of this macronutrient in this omnivorous species.

Sharpsnout seabream is a marine teleost of increasing interest for Mediterranean aquaculture, but there is still a lack of information regarding its circadian organization. In this study, we have investigated sharpsnout seabream locomotor activity, feeding and plasma melatonin daily rhythms under a 12:12-h LD cycle, as well as the persistence of locomotor activity circadian rhythmicity under constant light (LL) conditions. When submitted to an LD cycle, most sharpsnout seabream displayed a diurnal locomotor pattern, with an average 74% of activity recorded during daytime. However, along the experiment 40% of fish spontaneously changed their locomotor rhythm phasing and became nocturnal. Feeding behaviour, nevertheless, remained strictly diurnal in all cases, with 97% of food demands being made during the light period. Free-running locomotor rhythms were recorded in one third of the fish kept under LL. Daily plasma melatonin levels displayed a rhythmic profile, with low daytime values (111 pg/ml) and high nighttime concentrations (791 pg/ml). Taken together, these results evidence a high degree of plasticity for sharpsnout seabream activity patterns, as well as phasing independence of locomotor and feeding rhythms. Finally, the existence of a well-defined daily rhythm of plasma melatonin was found.

Teleost fish are able to regulate their energy intake selecting from pure macronutrients sources, but the regulatory mechanisms involved in macronutrients selection remain unknown. Serotonin (5-HT) reduces food intake in mammals and fish and modifies the macronutrients selection pattern in mammals; however, no information is available about its role on macronutrients selection in fish. The aim was to determine the effect of orally administered 5-HT (0.1, 0.5 and 2.5 mg kg BW(-)(1)) into gelatine capsules on the subsequent macronutrient selection of sea bass, using for this purpose gelatine capsules including carbohydrates, protein, or lipids separately. The voluntary ingested 5-HT was released into the plasma of fish, reaching a level two times greater than the controls, 45 min after the ingestion of a capsule containing 2.5 mg kg BW(-1) of 5-HT. The indoleamine, at doses of 0.1, 0.5 and 2.5 mg kg BW(-1), produced a reduction in total food intake of 31%, 49% and 37%, respectively, compared to the baseline, modifying the macronutrient selection pattern. The percentage of fat selected was significantly reduced whereas the percentage of protein significantly increased after administration of highest dose, but no changes were observed in the proportion of carbohydrate for any 5-HT doses. In conclusion, oral administration of 5-HT affected both amount of food intake and pattern of macronutrients selected. This is the first evidence supporting a role of 5-HT as a neurohumoral mediator involved in macronutrients selection in fish.

Salinity is one of the most relevant environmental parameters in regards to fish physiology, modifying food intake and growth performance in many fish species; however, its possible effects on macronutrient selection are still unknown. The aim of this study was to determine the effects of three salinity levels (25 per thousand, 7 per thousand, and 0 per thousand) on total food intake and encapsulated macronutrient selection in a euryhaline teleost, European sea bass. A total of 40 fish (five per tank) with an average body weight of 52.4 +/- 7.1 g were used. Lowering the salinity level from 25 per thousand to 7 per thousand and 0 per thousand reduced food intake by 27% and 42%, respectively. Regarding macronutrient selection, these salinity changes significantly decreased the percentage of CH intake by 31% and 27%, while increasing that of P by 30% and 25%, respectively. Fat selection remained unaltered, with an average value of 22% for all tested salinities. Specific growth rate (SGR) and feed conversion efficiency (FCE) were affected by macronutrient selection pattern, which in turn was salinity-dependent. These results indicate a strong influence of salinity on European sea bass food intake and macronutrient selection.

Recent reports describe teleosts as being able to regulate energy intake by selecting from pure macronutrient sources, although the regulatory mechanisms involved in this selection remain unknown. The aim of the present work was to determine the effect of selective macronutrient deprivation on energy regulation and macronutrient selection, using for this purpose carbohydrate (CH), protein (P), and fat (F) packaged separately into gelatin capsules, a method that prevents the diet chemosensory properties at oropharyngeal level from interfering with macronutrient selection. Twenty-four individually housed sea bass (Dicentrarchus labrax) were subjected to two experiments: (a) two-macronutrient deprivation, and (b) one-macronutrient deprivation. In two-macronutrient deprivation, fish were fed sequentially with P, CH, or F, and in one-macronutrient deprivation, they were fed sequentially with two separately packaged macronutrients (P and CH, CH and F, or P and F). There was a rapid reduction of macronutrient intake in two-macronutrient deprivation, reaching 80% inhibition after 4, 5, and 7 days of P, CH, and F intake, respectively. In one-macronutrient deprivation, the energy intake was significantly reduced during selective F deprivation, but not with P or CH deprivation. Although the fish were being fed with only two macronutrients, the relative proportions of these macronutrients in each selective deprivation phase were the same as the baseline. These results show that in deprivation studies fish need at least F plus one other macronutrient to regulate their energy intake, and that their macronutrient selection is stable even when one is absent. In summary, fish seem to regulate energy and macronutrient selection through post-ingestive mechanisms probably involving chemosensory detection in the gut, and/or post-absorptive mechanisms.

Tench (Tinca tinca) has been described as a strictly nocturnal species whose locomotor activity rhythms, albeit strongly synchronised by light, have an endogenous nature. Aside from light, a number of other environmental factors, such as mealtime, can act as circadian system synchronisers in fish; however, there is a scarcity of information on tench feeding rhythms. This study describes daily self-feeding rhythms in tench, and analyses the role of feeding time on synchronisation of locomotor activity rhythms. Tench were able to operate string sensor-activated self-feeders, and they displayed a strictly nocturnal behavior, both under indoor and outdoor conditions. Locomotor activity remained strictly nocturnal irrespective of whether tench were fed only during the scotophase (D-feeding) or the photophase (L-feeding). However, no statistically significant differences were detected between both groups in terms of food intake or growth performance. Furthermore, unlike L-feeding, D-feeding elicited a clear anticipatory activity (FAA). When tench were given the possibility of feeding at both times of the day, they showed a clear preference for D-feeding. Finally, in fish exposed to constant darkness (DD), feeding time acted as a true zeitgeber and FAA was observed. When animals were fasted under DD conditions, locomotor activity free-run and 6 out of 12 individuals yielded significant results in the periodogram analysis. Under DD, fish resynchronised when regular food was resumed, with some tench displaying FAA. The obtained results indicated the existence of a feeding-entrainable oscillator (FEO) in tench.

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 degrees 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 synchronizing locomotor activity and melatonin rhythms in the Senegal sole, whose nocturnal habits should be taken into account for their rearing by aquaculture.

The role of the food orosensory properties on protein (P), fat (F) and carbohydrate (CH) self-selection was investigated in fish fed gelatine capsules containing pure macronutrients. A total of 40 sea bass (39.6+/-6.2 g initial body weight) distributed in eight 75-l tanks were used. In a sequence of experimental phases, sea bass were fed a pelleted complete diet, an encapsulated complete diet or a combination of separately encapsulated pure macronutrients. In order to induce associative learning, capsules containing a given macronutrient were paired with a particular colour. Our results demonstrate that fish are able to regulate food intake, so as to balance their energy intake, when they are fed a complete encapsulated diet and, therefore, without using the orosensory properties of the diet. Moreover, sea bass learn to discriminate and select among colour-coded, pure macronutrient capsules to compose a complete and balanced diet using colour as the only external cue. The composition of selected diet was 55% P, 23% CH and 22% F in terms of macronutrient percentage. The diet orosensory properties do not seem to be necessary to regulate macronutrient intake either, suggesting that an associative learning between capsule colour and content can be established through monitoring of macronutrient intake by postingestive and/or postabsorptive mechanisms. These results provide the first insight into energy and macronutrient self-selection by fish fed on gelatine capsules containing separate macronutrients.

The influence of two different fasting periods on macronutrient self-selection during refeeding was studied in sea bass. Twelve groups of three sea bass were kept under laboratory conditions with a 12:12 light-dark cycle and at 22.5 degrees C. Each aquarium was provided with three self-feeders containing three different diets made up of two macronutrients: protein-fat, protein-carbohydrate, and carbohydrate-fat. The fish were allowed to acclimatise to the diets and laboratory conditions in 4 weeks, during which they selected a baseline diet of 51% protein, 16.5% carbohydrate, and 32.5% fat, in terms of digestible energy. The fish were then deprived of food for 6 days, after which they were permitted to refeed. When food demands stabilised, they were subjected to total food deprivation for another 2 weeks. The total energy demanded from all the macronutrients increased significantly during the first day after both fasting periods. The proportion of macronutrient self-selection after fasting periods remained unchanged in respect to the baseline, except for protein energy which remained high in the two first days of refeeding after the second fasting period (the 51% of total demanded energy from protein during the baseline period rising to 60%). In short, after two short fasting periods of different length, sea bass showed a compensatory ingestion of energy, with a slightly increased demand from protein after the longest fasting period.

The pineal organ and its secretory product melatonin are regarded as synchronizers of daily rhythms to the external light/dark (LD) cycle. In fish, the pineal organ acts as a direct photoreceptor, transducing light information into neural and humoral (melatonin) signals. In the present study, we investigate a possible role for the pineal organ and melatonin in the regulation of feeding rhythms of rainbow trout, Oncorhynchus mykiss. We used individual rainbow trout placed in an insulated room at constant temperature (14 degrees C). Fish were self-fed ad lib by means of self-feeders coupled to a computer that continuously recorded demand-feeding activity. Before and after pinealectomy, the fish were exposed to a LD cycle of 16:8 h and then constant light (LL) to test the effect of pinealectomy on demand-feeding rhythms. Feeding records revealed that trout fed exclusively during daytime (96% of feeding confined to the light phase), and that removal of the pineal organ did not disrupt this daily feeding profile, with synchronization to the LD cycle persisting. Moreover, the appearance of circadian feeding rhythms was not affected by pinealectomy: most of the operated fish free-ran with an average tau longer than 24 h. Plasma melatonin rhythms persisted in the pinealectomized trout, but with small amplitude. These results suggest that the pineal may not be the site of the pacemaker that controls feeding rhythms in trout, although further research is required to study the involvement of other photoperiod-transducing systems and melatonin (of nonpineal origin) in the regulation and expression of circadian rhythms in this species.

The effect of 4-h feeding cycles on the feeding pattern of rats kept under constant light and constant darkness, was analysed. In both cases, the scheduled pattern of food-approach behavior elicited dissociation of the feeding activity into several components associated to the feeding times (CAFT), which coexisted with the previous circadian free-running rhythms. In LL rats and in the rest phase of DD animals, the CAFT was characterized by an increased number of food approaches confined exclusively to the period of food availability, with poor anticipatory activity. However, in the active phase of some DD rats, CAFT included an additional anticipatory activity. The interaction between the CAFT and the free-running rhythms involved modulation of the CAFT, depending on the free-running periodicity. After termination of the feeding-restriction schedule, some DD and LL animals retained the CAFT for at least 3 days. However, when the access to food was blocked 10 days after ending the restricted schedule, rats did not show any feeding activity associated to the previous feeding times. A spontaneous feeding pattern similar to that imposed by the previous feeding schedule emerged immediately after food deprivation in two of the DD animals. Although these results are compatible with the existence of a food-entrainable pacemaker, the existence of a multioscillatory light-entrainable pacemaker with some oscillators entrained by food pulses and others free-running may explain our results.

The objective of this research was to test the ability of rainbow trout to feed on, and select from, three "pure" macronutrient diets formulated to contain only one macronutrient (protein, fat, and carbohydrate). The three diets were offered to fish in three different self-feeders, the fish having to choose from them in order to compose a nutritionally balanced diet. A total of 12 trout (115 g initial body weight) were held individually in 57 liter tanks at a constant 14 degrees C. The results demonstrated that the trout were capable of composing their own complete diet, with a higher preference for protein than fat and carbohydrate. Food intake was regulated to balance energy intake and maintain steady growth. Trout showed a strict diurnal feeding rhythm, which free run under constant light with an endogenous period ranging from 18.2 to 27.7 h. These results provide the first insight into macronutrient self-selection in trout and valuable information on their feeding preferences, which may be taken into consideration when investigating fish nutrition, feeding regulation, and the design of adequate diets.

In the wild, both food availability and an animal's requirements may fluctuate. Given the choice to feed on different diets, animals may exhibit preferences in their selection. Although macronutrient selection has been investigated in mammals and birds, few attempts have been made to investigate dietary selection in fish. In the present study we investigate the feeding of goldfish on three "pure" macronutrient diets. Twelve single goldfish and one group of four goldfish, initially weighing 163.1 +/- 7.4 and 70.2 +/- 8.0 g, respectively, were maintained in 54-liter tanks at 20 degrees C under a 12 h:12 h light-dark (LD) cycle. Three pelleted diets were made containing 50% of each macronutrient: protein (casein + gelatin), fat (fish oil + soy oil), or carbohydrate (dextrin). All the diets included mixtures of vitamins and minerals, a binder (sodium alginate), and cellulose as a filler. During trials, three self-feeding devices delivering the protein, fat, or carbohydrate diet were installed in each aquarium. Goldfish soon learned to select from among the three diets. Overall daily food and digestible energy demands differed significantly between macronutrients. The demand for protein was lower than that for carbohydrate (16.6 and 33.7 g/kg BW/day, respectively), and the digestible energy demand for protein was lower than for fat (108.6 and 308.5 kJ/kg BW/day, respectively). Goldfish made their dietary selections on the basis of energy content, so that food demand increased to compensate for changes in the digestible energy density of the diets. Correlation analysis revealed a significant positive relationship between carbohydrate and fat demand (n = 8), whereas there were significant negative (n = 3) and positive (n = 1) relationships between protein and fat. Different daily patterns for the selection of each macronutrient were detected in some fish (i.e., carbohydrate during daytime, protein at the beginning of the night, and fat during the transition phase). In short, our results demonstrated the ability of goldfish to compose their own diet from three basic macronutrients, highlighting the complex pattern of behavior in their selection. Therefore, these new findings should be considered when studying feeding rhythms and the design of diets for fish.

The daily caloric intake and circadian pattern of macronutrient self-selection were examined in rats subjected to 3 h of food and water deprivation at the beginning or at the end of darkness. When one sole 3-h period of deprivation was applied, rats showed a compensatory response characterized by an unscheduled diurnal and nocturnal increase in the intake of the three macronutrients. However, repeated short restrictions during 15 days promoted a scheduled time-dependent feeding response, characterized by an exclusive increase in carbohydrate and fat intake and a decrease in protein intake. Repeated deprivation at the onset of dark produced a feeding response confined to the dark phase, while late dark deprivation produced both a diurnal and nocturnal increase in feeding. After 15 days of repeated restriction, rats showed no body weight variations with respect to control rats fed ad libitum. These results show that short fasting elicits a time- and macronutrient-dependent feeding response in rats, which involves reorganization of the macronutrient self-selection pattern to promote a total daily caloric compensation. These results suggest that animals principally respond to the energy deficit produced by restriction.

Daily variations of insulin, cortisol, and glucose are studied in animals adapted to two different photoperiodic regimes, with the intervals between feeding times and photoperiodic events kept constant. Data support the existence of a daily rhythm of plasma glucose which seems to be photoperiodic. In contrast, the daily patterns of insulin in sea bass seem to be mainly influenced by feeding time; however, an effect of photoperiod can not be excluded. When the digestive tract is absent of food, insulin levels are generally minimal at feeding times and maximal during the inter-meals periods, suggesting the central control of insulin secretion during short-term food deprivation. Contrarily, the nadir values of plasma cortisol were reached at midday during the inter-meal period and peak plasma levels were evident at both light onset and offset. Disruption between metabolite and hormone patterns suggest that they are under different controls. Such results could be explained under the existence of a multioscillator system, including a food entrainable oscillator in addition to the master light entrainable oscillator.

The existence of feeding rhythms implies that fish would feed better during their preferred feeding phase but reject food at any other time. In the present paper, we tested the performance of a new device for continuously collecting and detecting uneaten food pellets. The device is basically made of two parts: a pellet collector placed just under the feeder and a decanter with a sensor attached to the bottom. When a food pellet was not eaten, it was rapidly collected and transferred to the decanter, where it was detected while dropping by an infrared sensor coupled to a microcomputer. To validate this system, five groups of fifteen sea bass, Dicentrachus labrax L., were maintained under natural conditions and subjected to a daily feeding cycle (feeding rate = 2.5% of body weight) consisting of three meals of one hour duration each (0800-0900 h, 1600-1700 h and 2400-0100 h). Uneaten pellets together with demand-feeding activity were simultaneously recorded. In addition to these test tanks, "natural" demand-feeding rhythms were also investigated in five groups of sea bass maintained under an ad lib self-feeding regime. In the test tanks, when submitted to the three meal feeding cycle, sea bass showed clear time preferences for feeding, since they fed mostly during the morning and afternoon, rejecting food at night. Consequently, the profile of uneaten pellets peaked at night butt remained very low during daytime. This diurnal preference for feeding is consistent with the almost strict diurnal feeding rhythm found in the sea bass groups under ad lib self-feeding. These results revealed the usefulness of this device in estimating food utilization and its potential application in nutritional and chronobiological studies in fish.

In contrast to the common diurnal and nocturnal ways of life, some fish species have been shown to have a dual phasing behaviour. Therefore, the daily pattern of behaviour is not always rigidly confined to the light or dark phase and a diurnal fish may become nocturnal and vice versa. In the present study, the locomotor and feeding activities of single goldfish were simultaneously investigated to examine the existence of such dual behaviour. Nineteen goldfish weighing 97.2 g on average were placed individually in 35-1 glass tanks equipped with an infrared sensor and a newly developed self-feeding device. Fish were exposed to a light:dark (LD) 12:12 h cycle, constant darkness (DD), and 45:45 min LD pulses to study endogenous rhythmicity. Under LD 12:12, the daily pattern of behaviour differed between individual fish; some goldfish were diurnal and others were nocturnal. Furthermore, some of them displayed an extraordinary flexibility in phasing because they were light active but dark feeding, and vice versa. Generally, goldfish tended to be day active, although their feeding habits appeared equally distributed between light and dark phases. Under DD, goldfish showed free-running rhythms that averaged 25.3 +/- 1.8 h and 24.4 +/- 1.7 h for locomotor activity and feeding, respectively, but that were slightly shorter under LD pulses. These results indicate that the type of phasing of locomotor activity did not necessarily decide the feeding phase; much of this is explained by the fact that goldfish were self-fed. Flexibility in phasing and a certain degree of independence between locomotor and feeding activities could be seen as an adaptative response of the highly adaptable circadian system of fish.

We describe and test a programmable feeding system based on a contact eatometer, previously developed in our laboratory, consisting of a swinging grid beneath a hopper that is moved by the rat each time it wants to eat. This has not been connected to a solenoid that can block the movement of the grid to prevent access to the food. It also provides a continuous record of food approaches even during restricted periods when no food is made available, and so it is useful in studying the synchronizing role of food in the circadian rhythms of feeding behavior. The simplicity and cheapness of its construction and the effective blocking of access to food make it an ideal tool in chronobiological studies involving the simultaneous use over long periods of a large number of animals.

Sea bass, a fish species characterized by its dualistic feeding pattern, was investigated to study the synchronizing effect of light and food on the demand-feeding rhythm. Nocturnal and diurnal sea bass, both in groups and individually, were exposed to restricted-feeding (RF) and light-dark (LD) cycles of different periods. The phase relationship between both zeitgebers was also studied. The results show that food-demand rhythms synchronize to periodic food availability under constant light conditions (DD) and that there is a partial coupling between food-entrained and light-entrained activity under conflicting zeitgebers (LD 13:13 h and RF 4:20 h), suggesting the existence of a feeding entrainable oscillator (FEO) in addition to the master light entrainable oscillator (LEO). In some cases, food availability restricted to the light or dark phase contrary to that of the previous feeding phase changed a diurnal feeding pattern into nocturnal and viceversa, suggesting that food can be one of the switching factors that decides whether the circadian system of sea bass is nocturnal or diurnal. However, the fact that the feeding pattern of some fish was unrelated with the phase in which food was available suggests that other internal and/or external factors could be involved in the temporal flexibility of sea bass.

The purpose of this work is to test whether physiological factors, such as body weight or food intake, are related to the period of environmental cycles under which animals are kept. We studied body weight increase, daily food intake and efficiency (i.e. relationship between body weight increase and food intake) of 7 groups each containing 20-24 male rats. Measurements were recorded every 4 days from the day of weaning (25 days old) during 64 days. Each group of rats was kept under a symmetrical LD cycle. The period of the cycles studied were: 22, 23, 24, 25, 26, 27 and 28 hours (T22, T23 ... T28). Results show differences in the three variables studied for groups T25 and T26. These animals show an inferior body weight, less food intake and less efficiency. It would seem that the difference between the period of the external LD cycle and the endogenous period of the animals rhythm induces changes in the energetic needs of the organism.

A new contact eatometer designed and built in our laboratory is described. The system makes possible the reliable continuous recording of feeding behavior in rats from the time of weaning, without significantly affecting food intake- and growth-related variables. Improved time discrimination and reliability of records--along with the small financial outlay necessary to manufacture the device--make the system appropriate for chronobiological studies which involve the simultaneous use of a large number of animals.

A new demand feeder was designed for the automatic and accurate feeding of fish. The feeding device is microcomputer controlled and permits the continuous recording of feeding behaviour. The electromechanical feeder consists of a sliding door powered by a solenoid which provides only one weighed pellet when activated by the fish. Some preliminary results on feeding behaviour in sea bass are presented to test the efficiency of the feeder.

The effect of neonatal androgenization with testosterone propionate (TP) on growth, food intake, and feeding circadian and ultradian rhythms was studied in male and female rats. TP-female rats but not TP-male rats weighed more and ate more in adulthood than control animals injected with oil. TP administration to male rats induced few changes in the circadian organization of food intake and meal size. However, neonatal androgenization of female rats produced an approach of feeding parameters to those showed by male rats: diminished meal number and increased meal size and food intake. Moreover, the spectral analysis of meal frequency revealed that TP induced in female rats an enlargement in the 4.8 h ultradian component. Although hormone secretions produced in adult animals contribute to sexual dimorphism, it is noticeable that androgen presence during the organizational period is largely responsible for differences between sexes.