Feeding Rhythms Research Articles

The seasonal distribution, diel vertical distribution and feeding behavior of Paraeuchaeta concinna in the shallow subtropical coastal waters of eastern Hong Kong

BackgroundPredatory copepods of the family Euchaetidae are widely distributed in polar, temperate, subtropical and tropical oceans. Paraeuchaeta concinna is the most abundant Euchaetidae in the subtropical coastal seas of Hong Kong and southern China. However, compared to Euchaetidae species in temperate and polar regions, relatively little information is available on the ecology of P. concinna and other Euchaetidae species in the subtropical oceans. This paper provides information on the seasonal abundance of P. concinna in the coastal seas of eastern Hong Kong. The diel vertical distribution of P. concinna, feeding behavior, and predation impact on mesozooplankton in eastern Hong Kong were also investigated.ResultsP. concinna is most abundant in winter and spring. Their abundance decreases shoreward, and densities are generally higher in the open waters of eastern Hong Kong than in the inner parts of Mirs Bay and Tolo Harbour. P. concinna exhibits both diel vertical migration and diel feeding rhythms in Mirs Bay. P. concinna females show strong preference for the copepods of the genera Acrocalanus, Paracalanus, and Parvocalanus, and remove ~4% of their standing stocks daily.ConclusionsThe low abundance of P. concinna during most of the year suggests it is not indigenous to coastal seas of eastern Hong Kong. P. concinna performs diel vertical migration, most likely as a strategy to avoid visual predation. Gut content analysis showed that Acrocalanus, Paracalanus, and Parvocalanus are highly preferred prey of P. concinna. A daily predation impact of ~4% of the standing stocks of Acrocalanus, Paracalanus, and Parvocalanus suggests that P. concinna may play an important role in regulating the populations of these small copepods in Mirs Bay, especially during winter and spring.

Peroxisome proliferator-activated receptor α (PPARα) activation advances locomotor activity and feeding daily rhythms in mice

Peroxisome proliferator-activated receptors (PPARs) are key mediators of energy homeostasis, and lipid and glucose metabolism that exhibit circadian expression. PPAR activating drugs are used clinically as lipid and glucose-lowering drugs. We evaluated the effect of long-term (11 weeks) PPARα and PPARγ activation using bezafibrate and rosiglitazone, respectively, on metabolism, locomotor activity and feeding rhythms of non-obese mice. We found that bezafibrate, but not rosiglitazone, led to no weight gain and a slight weight loss with reduced epididymal fat pads. Although rosiglitazone had a minor effect on 24-h food intake rhythm, bezafibrate treatment was accompanied by increased amplitude and an advanced acrophase of the 24-h feeding rhythm. Similarly, unlike rosiglitazone, bezafibrate treatment was accompanied by a significantly advanced acrophase of locomotor activity rhythm under constant darkness conditions. As disrupted circadian rhythms lead to obesity, PPARα activation can serve as a clinical target for the modulation of both circadian rhythms and metabolism.

The Use of Self-Feeders in Carp ( Cyprinus carpio ) Cultured Production

SUMMARY In aquaculture there is a need to better understand feeding rhythms in order to facilitate a good match between the timing of feed distributio n and fish biological rhythms. Further, feeding the fish at the appropriate time may reduce feed wastage in aquaculture systems. The aim of the present paper is to evaluate the use of self-feeders in carp culture production. The basic idea with self-feeders is tha t the fish themselves control the feeding level, which is thereby set by their feeding motiva tion. To determine the limitations of the technique this work has focused on characterizing: (1) how self-feeding activity is related to food demand and (2) how the self-service food suppl y is related to growth and feed conversion ratios. For the feeding system to function correctly, carp must first learn how to operate it. Carp reared in cage in groups of 100 individuals re quire about 12 days reaching a stable level of self-feeding. Under large-scale rearing conditio ns (e.g. in cages with group sizes of 10002000 fish), however, learning seems to be of minor importance for the ability of fish to operate the system. When reared in small tanks in g roups of up to about 300 fish, self-feeding activity in carp is strongly influenced by the deve lopment of dominance hierarchies. Under such situations, a small number of fish will domina te the activation of the trigger and thereby have a disproportionately greater influence on the food supply of the group as a whole. Carp fed using the demand feeding technique and restricted rations had the best-feed conversion, with a mean value of 1.08 during the ex periment (feed conversion=kg food supplied/kg weight gain). The feeding of carp using the unrestricted demand feeding technique resulted in a feed conversion of 1.29 and using restricted timer-controlled feeding it was 1.16. The reward level (amount of food received in respon se to one trigger actuation) is the single most important factor requiring proper adjus tment in order to optimize growth and feed conversion ratios when using self-feeding systems. High-density conditions reduce the selffeeding activity of carp, and the recommended maximum rearing density is about 30 kg m 3 . An evaluation of growth and feed conversion data in dicates that self-feeders have the potential to function well with carp under commerci al rearing conditions.

Circadian expression of clock and putative clock-controlled genes in skeletal muscle of the zebrafish

To identify circadian patterns of gene expression in skeletal muscle, adult male zebrafish were acclimated for 2 wk to a 12:12-h light-dark photoperiod and then exposed to continuous darkness for 86 h with ad libitum feeding. The increase in gut food content associated with the subjective light period was much diminished by the third cycle, enabling feeding and circadian rhythms to be distinguished. Expression of zebrafish paralogs of mammalian transcriptional activators of the circadian mechanism (bmal1, clock1, and rora) followed a rhythmic pattern with a ∼24-h periodicity. Peak expression of rora paralogs occurred at the beginning of the subjective light period [Zeitgeber time (ZT)07 and ZT02 for roraa and rorab], whereas the highest expression of bmal1 and clock paralogs occurred 12 h later (ZT13-15 and ZT16 for bmal and clock paralogs). Expression of the transcriptional repressors cry1a, per1a/1b, per2, per3, nr1d2a/2b, and nr1d1 also followed a circadian pattern with peak expression at ZT0-02. Expression of the two paralogs of cry2 occurred in phase with clock1a/1b. Duplicated genes had a high correlation of expression except for paralogs of clock1, nr1d2, and per1, with cry1b showing no circadian pattern. The highest expression difference was 9.2-fold for the activator bmal1b and 51.7-fold for the repressor per1a. Out of 32 candidate clock-controlled genes, only myf6, igfbp3, igfbp5b, and hsf2 showed circadian expression patterns. Igfbp3, igfbp5b, and myf6 were expressed in phase with clock1a/1b and had an average of twofold change in expression from peak to trough, whereas hsf2 transcripts were expressed in phase with cry1a and had a 7.2-fold-change in expression. The changes in expression of clock and clock-controlled genes observed during continuous darkness were also observed at similar ZTs in fish exposed to a normal photoperiod in a separate control experiment. The role of circadian clocks in regulating muscle maintenance and growth are discussed.

Effect of size grading on sea bass (Dicentrarchus labrax) juvenile self-feeding behaviour, social structure and culture performance

This study aims to test the influence of size grading on self-feeding behaviour, social structure (measured by the percentage of triggering acts per individual), growth performances, and blood physiological variables of individ- ually passive integrated transponder (PIT)-tagged sea bass juveniles, using a computerized on-demand feeding system coupled with a PIT tag monitoring device. Three consecutive periods of 27 days each were compared: a first period (P1) before grading (6 tanks of 100 fish; 40.2 ± 8.9 g) followed by a second period (P2) after grading. The protocol applied aimed to create two groups of fish of similar mean weight but with either a low or a high coefficient of variation of weight (CVw) corresponding to an imposed difference in social disruption (Tlow: CVw ~ 10%, 3 tanks of 60 fish each with social disruption; Thigh: CVw ~ 20%, 3 tanks of 60 fish each, without social disruption). Tlow and Thigh groups were studied over P2, and an additional 27-day period under identical conditions (P3). The grading protocol used and/or time modified the social structure when comparing P 1a ndP2. Thereafter, during P 2a ndP3, no difference could be observed in growth performances, feed demand, or physiological variables between Tlow and Thigh groups. Feeding rhythms and social structures were similar in both groups. In conclusion, such grading practice only transiently modifies feed de- mand behaviour and social structure built around the self-feeder, without further improvement in individual growth performances in sea bass.

Circadian integration of sleep-wake and feeding requires NPY receptor-expressing neurons in the mediobasal hypothalamus

Sleep and feeding rhythms are highly coordinated across the circadian cycle, but the brain sites responsible for this coordination are unknown. We examined the role of neuropeptide Y (NPY) receptor-expressing neurons in the mediobasal hypothalamus (MBH) in this process by injecting the targeted toxin, NPY-saporin (NPY-SAP), into the arcuate nucleus (Arc). NPY-SAP-lesioned rats were initially hyperphagic, became obese, exhibited sustained disruption of circadian feeding patterns, and had abnormal circadian distribution of sleep-wake patterns. Total amounts of rapid eye movement sleep (REMS) and non-REMS (NREMS) were not altered by NPY-SAP lesions, but a peak amount of REMS was permanently displaced to the dark period, and circadian variation in NREMS was eliminated. The phase reversal of REMS to the dark period by the lesion suggests that REMS timing is independently linked to the function of MBH NPY receptor-expressing neurons and is not dependent on NREMS pattern, which was altered but not phase reversed by the lesion. Sleep-wake patterns were altered in controls by restricting feeding to the light period, but were not altered in NPY-SAP rats by restricting feeding to either the light or dark period, indicating that disturbed sleep-wake patterns in lesioned rats were not secondary to changes in food intake. Sleep abnormalities persisted even after hyperphagia abated during the static phase of the lesion. Results suggest that the MBH is required for the essential task of integrating sleep-wake and feeding rhythms, a function that allows animals to accommodate changeable patterns of food availability. NPY receptor-expressing neurons are key components of this integrative function.

Quantitative Expression Profile of Distinct Functional Regions in the Adult Mouse Brain

The adult mammalian brain is composed of distinct regions with specialized roles including regulation of circadian clocks, feeding, sleep/awake, and seasonal rhythms. To find quantitative differences of expression among such various brain regions, we conducted the BrainStars (B*) project, in which we profiled the genome-wide expression of ∼50 small brain regions, including sensory centers, and centers for motion, time, memory, fear, and feeding. To avoid confounds from temporal differences in gene expression, we sampled each region every 4 hours for 24 hours, and pooled the samples for DNA-microarray assays. Therefore, we focused on spatial differences in gene expression. We used informatics to identify candidate genes with expression changes showing high or low expression in specific regions. We also identified candidate genes with stable expression across brain regions that can be used as new internal control genes, and ligand-receptor interactions of neurohormones and neurotransmitters. Through these analyses, we found 8,159 multi-state genes, 2,212 regional marker gene candidates for 44 small brain regions, 915 internal control gene candidates, and 23,864 inferred ligand-receptor interactions. We also found that these sets include well-known genes as well as novel candidate genes that might be related to specific functions in brain regions. We used our findings to develop an integrated database (http://brainstars.org/) for exploring genome-wide expression in the adult mouse brain, and have made this database openly accessible. These new resources will help accelerate the functional analysis of the mammalian brain and the elucidation of its regulatory network systems.

Seasonal Feeding Rhythm Associated with Fasting Period ofPangasianodon gigas: Long-Term Monitoring in an Aquarium

The Mekong giant catfish Pangasianodon gigas is endemic to the Mekong River basin, and is recognized as endangered species, largely due to overfishing and development of the river basin. We monitored food intake of P. gigas in a stable environment in an aquarium over a 6-year period and analyzed their feeding rhythm and fasting periods. The daily food intake for each fish was recorded from 18 June 2004 to 17 June 2010. The feeding rhythm or pattern was determined by the fast Fourier transform (FFT) analysis. The FFT analysis revealed that different cycles of feeding rhythm (168.8, 313.1, and 365.3 days) in three catfishes and no observable cycles in two catfishes. However, three catfishes showed subordinate peaks with approximately 365 days (365.3 days for all). These suggest that, at least, four of five catfish had have approximately 365-days feeding cycle. We also showed that all catfish undergo long-term fasting periods (> 20 days). Of note, the feeding/fasting pattern coincides with the wet/dry seasons in Thailand, which also corresponds to the abundance of the catfish food resource (Cladophora spp.). We found that P. gigas exhibit a seasonal feeding rhythm that is synchronized by food availability. Furthermore, we found that the seasonal feeding rhythm was gradually dampened over time, suggesting that the observed seasonal feeding rhythm with long-term fasting of the catfish is likely controlled by an endogenous clock system. To our knowledge, this is the first case of quantification of the seasonal feeding rhythm with fasting periods in teleost fish.

Does feeding time affect fish welfare?

Increased aquaculture production has raised concerns about managing protocols to safeguard the welfare of farmed fish, as consumers demand responsible aquaculture practices to provide 'welfare friendly' products. Feeding is one of the largest production cost in a fish farm and can be one of the biggest stressors for fish. Under farming conditions, fish are challenged with artificial diets and feeding regimes, and inadequate feeding conditions cause stress, alteration of normal behavioural patterns, poor performance and eventually diseases and death, which are by no means acceptable neither economically nor ethically. This review aims to highlight the impact of feeding rhythms and feeding time upon physiological and behavioural welfare indicators, which show circadian rhythms as well. Therefore, all these variables should be considered when designing feeding strategies in farming conditions and assessing the welfare state of cultured fish.

Examining the daily feeding rhythms of amago Oncorhynchus masou masou using self-feeding systems

Knowledge of circadian feeding rhythms in farmed fish species can help farmers determine the optimal feeding times to maximise feed consumption and minimise feed wastage. This study examined i) the circadian feeding rhythms, ii) the inter-day variability in feed demanded and iii) feed wastage of amago, Oncorhynchus masou masou, fed using self-feeding systems. Three replicate groups of 16 fish were held under a 12:12 light:dark cycle at 16 °C for 56 days. After a 28-day self-feeder acclimation period all three groups had become competent self-feeders and the treatment period ran from day 28 to day 56. Under the experimental light and temperature regime utilised amago appear to be visual self-feeders, actuating self-feeders almost exclusively during the light phase (99.9% of actuations). All three groups exhibited a distinct diurnal feeding rhythm within the light phase and demonstrated significant ( P < 0.05) crepuscular peaks in feed demand. In addition, one group also displayed a significant peak at midday. Daily ration varied both within and between groups but no clear rhythmicity was observed in these variations. Feed waste was very low (always < 2%) for each group. The results of this study suggest that farmers can optimise daily feed consumption by feeding amago exclusively during the light phase, specifically at dawn and dusk, with a possible extra meal at midday.

Characterization of melanocortin 4 receptor in Snakeskin Gourami and its expression in relation to daily feed intake and short-term fasting

In this study, melanocortin 4 receptor ( MC4R) was characterized in Snakeskin Gourami ( Trichogaster pectoralis) and designated as TpMC4R. The TpMC4R contained predicted regions that were structural features of MC4R subtypes of vertebrates. In addition, phylogenetic analyses showed that TpMC4R were in MC4R orthologues and closely related to piscine MC4Rs. The TpMC4R transcripts were detected in embryos at all developmental stages. Further, its mRNA was detectable in unfertilized eggs, suggesting that TpMC4R could be classified as maternal mRNA. Using real-time RT-PCR, graded expression at each central and peripheral tissue was demonstrated. Localization of TpMC4R expression in the brain was performed by in situ hybridization. An experiment was conducted to determine the expression profile of TpMC4R during daily feeding in each region of the brain. Fish were fed twice a day at 10:00 and 16:00, and the level of TpMC4R expression was analyzed at 9:00, 11:00, 13:00 and 15:00. The expression level of TpMC4R was significantly reduced at 15:00 compared to that at all previous times (9:00, 11:00 and 13:00). Moreover, significantly higher expression levels of TpMC4R were observed at 18- and 24-h fasting periods. The finding of variation in MC4R expression level during daily feeding and fasting period revealed some direct and/or indirect relations of the MC4R expression to circadian feeding rhythm and short-term food deprivation in fish.

Copepod feeding in a coastal area of active tidal mixing: diel and monthly variations of grazing impacts on phytoplankton biomass

AbstractThis study examined monthly feeding rates and grazing impact on phytoplankton biomass, as well as diel feeding rhythms of four key copepod species in a tidally well mixed estuary (Asan Bay, Korean Peninsula). Monthly ingestion rates estimated based on gut pigment analysis were closely associated with their peak densities, but not with phytoplankton biomass, implying high ingestion may be related to reproductive output for population growth. The three smaller copepods, Acartia hongi, Acartia pacifica and Paracalanus parvus, showed feeding preference for smaller phytoplankton (&lt;20 μm) with higher clearance rates, whereas the larger Calanus sinicus preferred larger phytoplankton. Acartia pacifica and P. parvus showed distinct increased nocturnal feeding rates as measured with gut fluorescence, whereas A. hongi showed no significant day–night differences. Copepod diel feeding patterns were not associated with food quantity, and endogenous physiological rhythm might be hypothesized as responsible for the observed diel feeding patterns. Grazing impact on phytoplankton biomass by the four copepods in the estuary was on average 8% (range 0.2–29.8%) of the phytoplankton standing stock, similar to values reported in other coastal waters. Very high copepod abundances but low daily carbon ration (&lt;20% for all copepods) provided by feeding on phytoplankton indicate that copepods also grazed on other non‐phytoplankton foods in Asan Bay.

Comparative characteristics of food supply of Pacific salmon (Oncorhynchus spp.) in the Bering Sea from 2002 to 2006

Based on complex epipelagic surveys in the western Bering Sea, a comparative analysis of food supply of Pacific salmon (Oncorhynchus spp.) was conducted in summer and fall from 2002 to 2006. Nine indirect indices of food supply used in the study were as follows: feeding similarity, width of the feeding spectrum, diet feeding ration, diet feeding rhythms, fraction of accessory food in the ration, growth rate of the fish, abundance of food resources, and abundance of salmon. The food supply of salmon is lower in summer 2003 and fall 2006 in comparison to the food supply in other years of the study. However, well expressed feeding selectivity, consumption of prey items of certain type, and small proportion of accessory food (copepods and chaetognaths) prevailed in plankton, suggests the presence of sufficient food resources for Pacific salmon in the western Bering Sea.

Metabolic Cycles Are Linked to the Cardiovascular Diurnal Rhythm in Rats with Essential Hypertension

BackgroundThe loss of diurnal rhythm in blood pressure (BP) is an important predictor of end-organ damage in hypertensive and diabetic patients. Recent evidence has suggested that two major physiological circadian rhythms, the metabolic and cardiovascular rhythms, are subject to regulation by overlapping molecular pathways, indicating that dysregulation of metabolic cycles could desynchronize the normal diurnal rhythm of BP with the daily light/dark cycle. However, little is known about the impact of changes in metabolic cycles on BP diurnal rhythm.Methodology/Principal FindingsTo test the hypothesis that feeding-fasting cycles could affect the diurnal pattern of BP, we used spontaneously hypertensive rats (SHR) which develop essential hypertension with disrupted diurnal BP rhythms and examined whether abnormal BP rhythms in SHR were caused by alteration in the daily feeding rhythm. We found that SHR exhibit attenuated feeding rhythm which accompanies disrupted rhythms in metabolic gene expression not only in metabolic tissues but also in cardiovascular tissues. More importantly, the correction of abnormal feeding rhythms in SHR restored the daily BP rhythm and was accompanied by changes in the timing of expression of key circadian and metabolic genes in cardiovascular tissues.Conclusions/SignificanceThese results indicate that the metabolic cycle is an important determinant of the cardiovascular diurnal rhythm and that disrupted BP rhythms in hypertensive patients can be normalized by manipulating feeding cycles.

Self-feeding behavior changes induced by a first and a second generation of domestication or selection for growth in the European sea bass,Dicentrarchus labrax

Among the strategies that can be used to improve fish welfare in a rearing environment, domestication and/or selective breeding was proposed to minimize fish responsiveness to husbandry practices. To verify this hypothesis on a recently domesticated species, the sea bass Dicentrarchus labrax, two experiments were realized, each using two populations differing according to their level of domestication or selection. For the first experiment, we used one population produced from wild parents (Wild; initial body mass: 106 ± 3 g), and one population from parents selected for growth for one generation (Selected 1; initial body mass: 129 ± 4 g). For the second experiment, we used one population produced from parents domesticated for two generations (Domesticated; initial body mass: 72 ± 3g ), and one produced from parents selected for growth for two generations (Selected 2; initial body mass: 89 ± 4 g). The first experiment was carried out over 112 days with 240 fish (60 fish per tank, 120 fish per population), and the second one over 84 days with 200 fish (50 fish per tank, 100 fish per population). Two variables, self-feeding behavior and growth performance, were measured over the time of the experiments. After a control period, the fish were submitted twice, at three-week intervals, to an acute stress treatment consisting of draining the tank and leaving the fish out of water for one minute. Both self-feeding behavior and growth performance were altered by the acute stress treatment. During the first post-stress period, the Domesticated and Selected (1 and 2) groups showed more pronounced post-stress exposure responses than the Wild fish: they modified their feeding rhythm, their feed intake, and their growth rate. During the second post-stress period, feeding rhythm was still affected (being more diurnal with a well defined peak), but the feed intake and growth rate results showed that the Domesticated and Wild groups seemed less affected than the Selected (1 and 2) populations, which continued to express a high post-stress response. According to these results, it can be concluded that: (1) an application of two acute stress treatments, at three-week intervals, modified fish feeding behavior and growth performance; (2) the domestication process seemed to improve fish adaptation abilities to this kind of stress; and (3) the process of selection for growth led to a final, better growth, but did not seem to improve fish acute stress tolerance.

Histaminergic Mechanisms for Modulation of Memory Systems

Encoding for several memory types requires neural changes and the activity of distinct regions across the brain. These areas receive broad projections originating in nuclei located in the brainstem which are capable of modulating the activity of a particular area. The histaminergic system is one of the major modulatory systems, and it regulates basic homeostatic and higher functions including arousal, circadian, and feeding rhythms, and cognition. There is now evidence that histamine can modulate learning in different types of behavioral tasks, but the exact course of modulation and its mechanisms are controversial. In the present paper we review the involvement of the histaminergic system and the effects histaminergic receptor agonists/antagonists have on the performance of tasks associated with the main memory types as well as evidence provided by studies with knockout models. Thus, we aim to summarize the possible effects histamine has on modulation of circuits involved in memory formation.

Circadian Rhythms of Self-feeding and Locomotor Activity in Zebrafish (Danio Rerio)

To investigate daily feeding rhythms in zebrafish, the authors have developed a new self-feeding system with an infrared photocell acting as a food-demand sensor, which lets small-size fish such as zebrafish trigger a self-feeder. In this paper, the authors used eight groups of 20 fish. Locomotor activity rhythms were also investigated by means of infrared sensors. Under a 12 h:12 h light (L)-dark (D) cycle, zebrafish showed a clear nocturnal feeding pattern (88.0% of the total daily food-demands occurring in the dark phase), concentrated during the last 4 h of the dark phase. In contrast, locomotor activity was mostly diurnal (88.2% of total daily activity occurring in the light phase). Moreover, both feeding and locomotor rhythms were endogenously driven, as they persisted under free-running conditions. The average period length (τ) of the locomotor and feeding rhythms was shorter (τ = 22.9 h) and longer (τ = 24.6 h) than 24 h, respectively. During the time that food availability was restricted, fish could only feed during ZT0–ZT12 or ZT12–ZT16. This resulted in feeding activity being significantly modified according to feeding time, whereas the locomotor activity pattern remained synchronized to the LD cycle and did not change during this trial. These findings revealed an independent phasing between locomotor and feeding activities (which were mostly nocturnal or diurnal, respectively), thus supporting the concept of multioscillatory control of circadian rhythmicity in zebrafish. (Author correspondence: javisan@um.es)

Cholecystokinin (CCK) in Atlantic herring (Clupea harengus L.) — Ontogeny and effects of feeding and diurnal rhythms

Neural and alimentary cholecystokinin (CCK) levels in Atlantic herring, Clupea harengus, were analyzed from hatching to 40days after hatching (DAH). The head compartment representing the neural pool was quantitatively dominant (>80% of the total CCK content) while the digestive tract pool represented 6–10%. During ontogeny the CCK level in whole larvae increased almost 15-fold from 0 to 40 DAH, being particularly marked from 14 to 20 DAH. Larvae of 24 to 26 DAH were examined for potential occurrence of a circadian rhythm and to analyze the effects of feeding. Fed and fasted larvae were significantly different, where fed larvae showed higher CCK levels. There were large fluctuations in CCK levels analyzed at 3h intervals without an apparent diurnal pattern. Shorter sampling intervals of 1h in the morning when lights were switched gradually on and food was offered to the larvae demonstrated a marked drop in the relative gut CCK levels and a concurrent increase in the CCK carcass to gut ratio, 1h after introduction of food followed by a return to prefeeding levels after 2h. This response probably results from a release and re-synthesis of CCK in the gut after initiation of feeding. Taken together, these results support earlier reports that CCK participates in the regulation of digestive processes in herring larvae, but CCK does not seem to have a circadian rhythm independent of feeding.

Diurnal rhythm of feeding of larvae of little oilfish Comephorus dybowski (Comephoridae) in Baikal

Diurnal rhythm of feeding of larvae of little oilfish Comephorus dybowski (Comephoridae) in Baikal

High-fat diet-induced obesity in animal models

Epidemiological studies have shown a positive relationship between dietary fat intake and obesity. Since rats and mice show a similar relationship, they are considered an appropriate model for studying dietary obesity. The present paper describes the history of using high-fat diets to induce obesity in animals, aims to clarify the consequences of changing the amount and type of dietary fats on weight gain, body composition and adipose tissue cellularity, and explores the contribution of genetics and sex, as well as the biochemical basis and the roles of hormones such as leptin, insulin and ghrelin in animal models of dietary obesity. The major factors that contribute to dietary obesity - hyperphagia, energy density and post-ingestive effects of the dietary fat - are discussed. Other factors that affect dietary obesity including feeding rhythmicity, social factors and stress are highlighted. Finally, we comment on the reversibility of high-fat diet-induced obesity.