Food Intake In Fish Research Articles

Evidence of a metabolic fatty acid-sensing system in the hypothalamus and Brockmann bodies of rainbow trout: implications in food intake regulation

Enhanced lipid levels inhibit food intake in fish but no studies have characterized the possible mechanisms involved. We hypothesize that the presence of fatty acid (FA)-sensing mechanisms could be related to the control of food intake. Accordingly, we evaluated in the hypothalamus, hindbrain, and Brockmann bodies (BB) of rainbow trout changes in parameters related to fatty acid metabolism, transport of FA, nuclear receptors, and transcription factors involved in lipid metabolism, and components of the K(ATP) channel after intraperitoneal administration of different doses of oleic acid (long-chain fatty acid, LCFA) or octanoic acid (medium-chain fatty acid, MCFA). The increase in circulating LCFA or MCFA levels elicited an inhibition in food intake and induced in the hypothalamus a response compatible with fatty acid sensing in which fatty acid metabolism, binding to cluster of differentiation 36 (CD36), and mitochondrial activity are apparently involved, which is similar to that suggested in mammals except for the apparent capacity of rainbow trout to detect changes in MCFA levels. Changes in those hypothalamic pathways can be related to the control of food intake, since food intake was inhibited when FA metabolism was perturbed (using fatty acid synthase or acetyl-CoA carboxylase inhibitors) and changes in mRNA levels of specific neuropeptides such as neuropeptide Y and proopiomelancortin were also noticed. This response seems to be exclusive for the hypothalamus, since the other center controlling food intake (hindbrain) was unaffected by treatments. The results obtained in BB suggest that at least two of the components of a putative fatty acid-sensing system (based on fatty acid metabolism and binding to CD36) could be present. Therefore, the present study provides, for the first time in fish, evidence for a specific role for FA (MCFA and LCFA) as metabolic signals in hypothalamus and BB, where the detection of those FA can be associated with the control of food intake and hormone release.

Macronutrient-induced differences in food intake relate with hepatic oxidative metabolism and hypothalamic regulatory neuropeptides in rainbow trout (Oncorhynchus mykiss)

This study examines how dietary macronutrient-induced changes in voluntary food intake (FI) relate to changes in markers of hepatic oxidative metabolism and in the expression of FI regulatory neuropeptides in a teleost model, the rainbow trout. Rainbow trout were fed for 6weeks with one of four iso-energetic diets (2×2 factorial design), containing either a high (HP, ~500g·kg−1DM) or a low (LP, ~250g·kg−1DM) protein level (PL) with, at each PL, fat (diets HP-F and LP-F) being substituted by an iso-energetic amount of gelatinized corn starch (diets HP-St and LP-St) as non-protein energy source (ES). Irrespective of the dietary PL, FI (g·kg−0.8·d−1) and digestible energy intake (DEI, kJ·kg−0.8·d−1) were significantly (P<0.05) reduced by the iso-energetic replacement of fat by starch as non-protein ES. Interestingly, trout fed these St-diets had higher gene expression of markers of hepatic oxidative phosphorylation (OxPhos), i.e. ubiquinol-cytochrome c reductase subunit 2 (UCR2) and cytochrome oxidase subunit 4 (COX4) and of aerobic oxidative capacity (CS, citrate synthase), which paralleled glucokinase (GK) transcription. This positive relation suggests that glucose phosphorylation and markers of mitochondrial OxPhos are linked at the hepatic level and possibly triggered the observed reduction in FI. Moreover, trout displaying the reduced FI had higher cocaine amphetamine regulator transcript (CART) mRNA in hypothalamus, whereas neuropeptide Y (NPY) mRNA did not follow the macronutrient-induced changes in FI. Further studies are needed to unravel the mechanisms by which diet-induced changes in hepatic metabolism inform central feeding centers involved in the regulation of FI in fish.

The comparative endocrinology of feeding in fish: Insights and challenges

Studying the endocrine regulation of food intake in fish can be challenging due to the diversity in appetite-regulating hormones and the diversity within the fish group itself. Studies show that although the structure of the hormones is relatively conserved among vertebrates, their functions might vary between fish and mammals as well as among fish species. In addition, feeding behavior and the action of appetite regulators can be largely modulated by the feeding and reproductive status of the fish as well as the environment in which they evolve. This review gives a brief perspective of the endocrine regulation of feeding in fish, some of the methods used, and challenges encountered when using a comparative approach.

Behavioral effect of neuropeptides related to feeding regulation in fish

The hypothalamus, limbic system, and brainstem play an important role in the regulation of instinctive behavior. Many kinds of hypothalamic neuropeptides, such as orexin, ghrelin, neuropeptide Y, melanin-concentrating hormone, pituitary adenylate cyclase-activating polypeptide, corticotropin-releasing hormone, and diazepam-binding inhibitor-derived peptides, including the octadecaneuropeptide, have been implicated in the regulation of appetite and energy homeostasis in various models, including rodents and goldfish. Several of these neuropeptides also influence locomotor or psychomotor activity in rats and mice. The aim of this paper is to review the current knowledge on the psychophysiological effects of neuropeptides involved in the regulation of food intake in fish, and to examine their significance from a comparative point of view.

Stress alters food intake and glucosensing response in hypothalamus, hindbrain, liver, and Brockmann bodies of rainbow trout

In fish food intake is altered under stress conditions, and in a fish teleost model like rainbow trout food intake is associated with the activity of the glucosensor systems. Thus, we aimed to evaluate the possible interaction of stress with the response of glucosensor mechanisms in rainbow trout. Thus, we subjected rainbow trout (via intraperitoneal injections) to normoglycaemic (control), hypoglycaemic (4 mg.kg -1 bovine insulin) or hyperglycaemic (500 mg.kg -1 glucose body mass) conditions for 5 days under normal stocking density (NSD, 10 kg fish mass·m -3) or stress conditions induced by high stocking density (HSD, 70 kg fish mass·m -3). The experimental design was appropriate since hypoglycemia and hyperglycemia were observed in fish under NSD whereas in normoglycaemic fish HSD induced changes in stress-related parameters similar to those reported in fish literature, such as increased levels of cortisol and glucose in plasma and decreased levels of glycogen in liver. Food intake did not respond to changes in plasma glucose levels in fish under HSD conditions, in contrast with the decreased food intake observed when glucose levels increased in fish under NSD conditions. Moreover, the changes with the increase in plasma glucose levels in parameters involved in glucosensing in liver, Brockmann bodies (BB), hypothalamus, and hindbrain of fish in NSD either disappeared (DHAP and GAP levels, and GK, PK, and GPase activities in liver; glucose, DHAP and GAP levels in BB; glucose and DHAP levels, and GK and PK activities in hypothalamus; glycogen and DHAP levels, and GSase activity in hindbrain) or changed (cortisol levels in plasma; glycogen and GAP levels, and GSase and FBPase activities in liver; GK and PK activities in BB; GK and PK activities in hindbrain) in fish under HSD. Those changes suggest for the first time in fish the existence of an interaction between glucosensing capacity and stress. The readjustment in the activity of glucosensor systems is also associated with changes in food intake resulting in an inability of the fish to compensate with changes in food intake those of circulating glucose levels as observed in fish under non-stressed conditions.

Anandamide and AM251, via water, modulate food intake at central and peripheral level in fish

The endocannabinoid system is a major regulator of food intake in many animal species. Studies conducted so far have mostly focused on mammals, and, therefore, in this study, the role of the endocannabinoid system in food intake in the sea bream Sparus aurata was investigated. The effect of different doses of the endocannabinoid anandamide (AEA), administered via water, was evaluated after different exposure times (30, 60 and 120 min) at both physiological and molecular levels. The results obtained indicate that fish exposed to AEA via water present ∼1000-fold higher levels of AEA in both the brain and liver, which correlated with a significant increase in food intake and with the elevation of cannabinoid receptor 1 (CB 1) and neuropeptide Y (NPY) mRNA levels in the brain. A peripheral effect of AEA was also observed, since a time-dependent increase in hepatic CB 1 mRNA and protein levels was detected. These effects were attenuated by the administration, again via water, of a selective cannabinoid CB 1 receptor antagonist (AM251). These findings indicate that the endocannabinoid AEA, at doses that stimulate food intake in fish, concomitantly stimulates the expression of the orexigenic peptide NPY as well that of its own receptor, thereby potentially enhancing its effect on food consumption. In agreement with a role of AEA in food intake in S. aurata, we found increased brain levels of both this and the other endocannabinoid, 2-arachidonoylglycerol (2-AG), following food deprivation.

The goldfish (Carassius auratus) as a model for neuroendocrine signaling

Goldfish (Carassius auratus) are excellent model organisms for the neuroendocrine signaling and the regulation of reproduction in vertebrates. Goldfish also serve as useful model organisms in numerous other fields. In contrast to mammals, teleost fish do not have a median eminence; the anterior pituitary is innervated by numerous neuronal cell types and thus, pituitary hormone release is directly regulated. Here we briefly describe the neuroendocrine control of luteinizing hormone. Stimulation by gonadotropin-releasing hormone and a multitude of classical neurotransmitters and neuropeptides is opposed by the potent inhibitory actions of dopamine. The stimulatory actions of gamma-aminobutyric acid and serotonin are also discussed. We will focus on the development of a cDNA microarray composed of carp and goldfish sequences which has allowed us to examine neurotransmitter-regulated gene expression in the neuroendocrine brain and to investigate potential genomic interactions between these key neurotransmitter systems. We observed that isotocin (fish homologue of oxytocin) and activins are regulated by multiple neurotransmitters, which is discussed in light of their roles in reproduction in other species. We have also found that many novel and uncharacterized goldfish expressed sequence tags in the brain are also regulated by neurotransmitters. Their sites of production and whether they play a role in neuroendocrine signaling and control of reproduction remain to be determined. The transcriptomic tools developed to study reproduction could also be used to advance our understanding of neuroendocrine-immune interactions and the relationship between growth and food intake in fish.

Nonlinear time series analysis of food intake in the dab and the rainbow trout

Evidence suggests that dab and rainbow trout are able to quickly adjust their food intake to an appropriate level when offered novel diets. In addition day-to-day and meal-to-meal food intake varies greatly and meal timing is plastic. Why this is the case is not clear: Food intake in fish is influenced by many factors, however the hierarchy and mechanisms by which these interact is not yet fully understood. A model of food intake may be helpful to understand these phenomena; to determine model type it is necessary to understand the qualitative nature of food intake. Food intake can be regarded as an autoregressive (AR) time series, as the amount of food eaten at time t will be influenced by previous meals, and this allows food intake to be considered using time series analyses. Here, time series data were analysed using nonlinear techniques to obtain qualitative information from which evidence for the hierarchy of mechanisms controlling food intake may be drawn. Time series were obtained for a group of dab and individuals and a group of rainbow trout for analysis. Surrogate data sets were generated to test several null hypotheses describing linear processes and all proved significantly different to the real data, suggesting nonlinear dynamics. Examination of topography and recurrence diagrams suggested that all series were deterministic and non-stationary. The point correlation dimension (PD2i) suggested low-dimensional dynamics. Our findings suggest therefore that any model of appetite should create output that is deterministic, non-stationary, low-dimensional and having nonlinear dynamics.

Functions of melanin‐concentrating hormone in fish

Melanin-concentrating hormone (MCH) was originally discovered in fish, in which it causes aggregation or concentration of melanin granules in melanophores, thus regulating body color. MCH is a cyclic neuropeptide synthesized as a preprohormone in the hypothalamus of all vertebrates. Mammalian MCH plays an important role as a neurotransmitter or neuromodulator in regulating food intake and energy homeostasis. MCH signaling system may involve in regulating food intake also in fish. This neuropeptide binds to G-protein-coupled seven transmembrane receptor[s] to mediate its functions. This article reviews MCH and MCH receptor signaling systems in body color change and food intake in fish.

Food Intake in Fish

Food Intake in Fish

Voluntary food intake in fish, COST 827 Workshop, Reykjavik, Iceland

Voluntary food intake in fish, COST 827 Workshop, Reykjavik, Iceland

Appetite-Suppressing Effects of Urotensin I and Corticotropin-Releasing Hormone in Goldfish (Carassius auratus)

Fish urotensin I (UI), a member of the corticotropin-releasing hormone (CRH) family of peptides, is a potent inhibitor of food intake in mammals, yet the role of UI in the control of food intake in fish is not known. Therefore, to determine the acute effects of UI on appetite relative to those of CRH, goldfish were given intracerebroventricular (i.c.v.) injections of carp/goldfish UI and rat/human CRH (0.2–200 ng/g) and food intake was assessed for a 2-hour period after the injection. UI and CRH both suppressed food intake in a dose-related manner and UI (ED₅₀ = 3.8 ng/g) was significantly more potent than CRH (ED₅₀ = 43.1 ng/g). Pretreatment with the CRH receptor antagonist, α-helical CRH_(9–41), reversed the reduction in food intake induced by i.c.v. UI and CRH. To assess whether endogenous UI and CRH modulate fish appetite, goldfish were given intraperitoneal implants of the glucocorticoid receptor antagonist, RU-486 (50 and 100 µg/g), or the cortisol synthesis inhibitor, metyrapone (100 and 200 µg/g), and food intake was monitored over the following 72 h. Fish treated with either RU-486 or metyrapone were characterized by a sustained and dose-dependent reduction in food intake. Pretreatment with i.c.v. implants of α-helical CRH_(9–41) partially reversed the appetite-suppressing effects of RU-486 and metyrapone. In a parallel experiment, the effects of RU-486 (100 µg/g) and metyrapone (200 µg/g) intraperitoneal implants on brain UI and CRH gene expression were assessed. Relative to sham-implanted controls, fish treated with RU-486 or metyrapone had elevated UI mRNA levels in the hypothalamus and CRH mRNA levels in the telencephalon-preoptic brain region. Together, these results suggest that UI is a potent anorectic peptide in the brain of goldfish and that endogenous CRH-related peptides can play a physiological role in the control of fish appetite.

Brain regulation of growth hormone secretion and food intake in fish

Growth in fish is regulated by the brain neuroendocrine—growth hormone (GH)— insulin-like growth factor axis (Peter and Marchant, 1995; Peng and Peter, 1997). However, growth cannot be realized without adequate food intake. A question to be answered in fish is whether there is any connection between the regulation of food intake and the brain neuroendocrine — GH — insulin-like growth factor axis. An additional question of relevance to aquaculture is whether the brain neuroendocrine — GH — insulin-like growth factor axis and food intake can be manipulated to stimulate faster growth rates of farmed fish?

What hormones may regulate food intake in fish?

Resume This is an ovcmicw of thc hormoncs which may be involved in food intake control in fish, and some hypothetical pathways of thcir action arc givcn based on mammalian knowledge. Most of the observed effects of these hormones may result from four types of mechanisms, each hormone acting by one or several as follows: (1) hormones could have a direct effect on central nervous system centres, associated with food intake behaviour or via vagal afferent neurons; (2) an indirect effect may occur via the gut which slows gastrointestinal transit, thus rcsulting in stomach distention which activates vagal afferent neurons; (3) they could have an indirect cffcct, acting dircctly on intermediary metabolism via glucose, free fatty acids or amino acids mohilization or storage; (4) the last possible pathway is an indirect effect by modifying directly or indirectly secretions of other hormones involved in food intake control. Some of thesc hormones (CCK, PYY, glucagon, adrenalin) act as short-term factors which regulate meal ingestion and are generally inhibitory factors. On thc othcr hand, other hormones (GH, TH, and leptin) require more time to modify food intake behaviour, and appcar as stored calorie rcgulators. However, the orientation of hormones to short-terin or to long-term action is not always clear as it has been noted for insulin and glucocorticoids, and may depend on the hormonal and metabolite environment.

Pronounced Seasonal Differences in Appetite of Atlantic Salmon Parr, Salmo salar: Effects of Nutritional State and Life-History Strategy

1. External environmental influences (such as temperature and photoperiod) affect rates of food intake in fish. In species with variable life-history patterns, individual appetite might vary with the developmental strategy adopted in response to differing nutritional requirements. There may also have been selection for appetite to vary with the anticipated natural availability of food. 2. This study examines how appetite in Atlantic salmon parr varies seasonally, and how this seasonal variation is influenced by (a) diet quality, (b) nutritional status of fish and (c) sexual maturation in male parr. 3. All fish showed a marked peak in food intake in May of their second summer followed by a sudden loss of appetite (measured both as appetitive behaviour and as actual food intake); this anorexia was unrelated to temperature and may be an adaptation to anticipated seasonal variation in natural food availability. 4. Fish compensated for a reduction in the fat content of the diet by increasing their intake rate (after a period of reduced appetite). Early in the winter, fish with a low lipid content had an enhanced appetite, but this response disappeared as the winter progressed, probably because the need to maintain energy reserves diminishes as the winter progresses. 5. Sexual maturation in males had no consistent effect on appetite, although there was some evidence for a reduced intake a few months prior to spawning.

Bombesin-like immunoreactivity in the forebrain and pituitary and regulation of anterior pituitary hormone release by bombesin in goldfish.

The presence and distribution of bombesin (BBS)/gastrin-releasing peptide (GRP)-like immunoreactivity (IR) was examined in the goldfish pituitary and forebrain. BBS/GRP-like IR nerve fibres were consistently observed throughout the pituitary neurointermediate lobe (NIL); occasionally, BBS/GRP-like material was localized in cells and few fibres within the pars distalis. Within the goldfish forebrain, sparse, fine-beaded BBS/GRP-like IR fibres and few perikarya were detected in the preoptic hypothalamus. BBS/GRP-like IR material was also present in the ventro-posterior hypothalamus and the hypothalamic inferior lobes, and, in particular, within the nucleus lateral tuberis pars anterioris (NLTa) and nucleus lateral tuberis pars posterioris (NLTp), nucleus anterior tuberis (NAT), nucleus recessus lateralis (NRL), nucleus recessus posterioris (NRP), and the nucleus diffusus lobi inferioris (NDLI). Several BBS/GRP-like IR perikarya were observed in periventricular regions of the NLT, NRL, and NRP. Finally, BBS/GRP-like IR material was detected in the nucleus habenularis, the nucleus rotundus, several thalamic nuclei, and the optic tectum of the dorso-posterior diencephalon. The presence of BBS/GRP-like IR material within the preoptic hypothalamus, hypophysial stalk, and in the pituitary suggests that BBS-like peptides may regulate pituitary hormone release in fish. Perifusion of goldfish pituitary fragments with initial pulses of 0.1, 10, 100 or 1,000 nM BBS stimulated both growth hormone (GH) and gonadotropin (GtH-II) release. Repeated pulses of the same dose of BBS generally stimulated GH and GtH-II release to a similar magnitude. These studies provide initial evidence that BBS/GRP-like peptides are present within the central nervous system of teleost fish. The anatomical distribution of BBS/GRP-like IR in goldfish hypothalamic feeding center supports our previous report indicating a role for BBS in the central regulation of food intake in fish. Additionally, the presence of BBS/GRP-like IR material in the pituitary and brain areas associated with the regulation of anterior pituitary hormone secretion, as well as evidence demonstrating a direct action of BBS at the level of the goldfish pituitary to modify GH and GtH-II secretion, indicates that BBS/GRP-like peptides likely act to regulate pituitary hormone release in teleosts.

Neuropeptide Regulation of Feeding and Growth Hormone Secretion in Fish

In goldfish bombesin (BBS)/gastrin-releasing peptide (GRP)-like and cholecystokinin (CCK)/gastrin-likc immunoreactive (IR) peptidcs are present in the pituitary, and ventro-posterior hypothalamus and hypothalamic inferior lobes of the brain feeding centre. Receptor autoradiography studies in goldfish indicate BBS/GRP and CCK/ gastrin specific binding sites in similar pituitary and brain areas. BBS and sulfated CCK8 inhibit food intake in goldfish when administered either intraperitoneally (ip) or into the brain third ventricle (icv), and act concomitantly to elevate serum growth hormone (GH). BBS and CCK also stimulate GH release from perifused goldfish pituitary fragments. Overall, BBS and CCK have potent satiety effects in goldfish, and may provide links to the neuroendocrine system for postprandial GH regulation. Other neuroendocrine factors involved in the regulation of GH secretion, including neuropeptide Y, gonadotropin-releasing hormone and GH-releasing hormone may also play a role in altering food intake in fish.

Diethylpropion decreases food intake in fish

Daily food intake of 5 specimens ofHaplochromis burtoni, measured in a 30-min feeding session, was reduced by the application of water solutions of 2 and 4 mg/l diethylpropion (2-diethylamino-propiophenon).

An hypothesis on the control of food intake in fish

An hypothesis on the control of voluntary food intake (appetite) in fish is presented. According to the hypothesis, only two parameters are necessary to design a feeding regime which might result in maximum growth of fish in an aquaculture system. The necessary parameters are maximum voluntary food intake in one meal, and evacuation rate of the stomach. This hypothesis is discussed in relation to empirical data.