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Circadian Rhythms in Fish
Abstract
Circadian rhythms play a critical role in fish development and daily activities. Although a major circadian "master" clock, like the SCN of mammals, has not yet been identified in fish, indirect evidence suggests that a light-entrainable oscillator is present in fish brain. Furthermore, the structural and functional design of fish circadian systems is remarkably complicated. Photosensitive CNS-related clock organs (the pineal gland and retina), peripheral photosensitive tissues with autonomic circadian clocks, and presumed food- or temperature-entrainable circadian oscillator(s) all make for complex circadian machinery that must remain well coordinated and still be able to ensure physiological adaptation to a periodically changing environment. Such a multilevel structure of partially independent oscillators may explain the high interspecies variability observed in piscine circadian systems and substantial individual plasticity in fish behaviour and physiology. Studying these features will continue to contribute to a better understanding of the principal mechanisms involved in circadian clock functions. Data accumulated so far show that rest in fish has fundamental similarities to the behavioural manifestations of sleep in higher vertebrates. Analogous to sleep in mammals, fish show a compensatory rest rebound, reducing locomotor activity and increasing arousal thresholds after a period of rest deprivation, suggesting that fish exert a homeostatic control on rest behaviour. Furthermore, rest in fish is regulated by the circadian system, because periodic reduction in locomotor activity and increase in arousal threshold are maintained in constant darkness and occur during the subjective night. These observations, together with the hypnotic effects of melatonin and sleep-inducing agents of the benzodiazepine and barbiturate families, indicate that rest behaviour in fish can be considered a sleeplike state. Studying sleep in fish may prove to be very productive in deciphering both the enigmatic function and the physiological mechanisms of sleep.
... Circadian rhythmicity helps fish to estimate time intervals and relies strongly on environmental cues (food availability and temperature) and on their synchronisation with photoperiod. Interestingly, the circadian rhythm may show intra-and interspecies variations (reviews: Frøland Steindal & Whitmore, 2019; Madrid et al., 2001;Zhdanova & Reebs, 2005); furthermore, even in the absence of any environmental cues, the biological clock autonomously oscillates with a circadian period (Zhdanova & Reebs, 2005). Fish can thus temporally ...
... Circadian rhythmicity helps fish to estimate time intervals and relies strongly on environmental cues (food availability and temperature) and on their synchronisation with photoperiod. Interestingly, the circadian rhythm may show intra-and interspecies variations (reviews: Frøland Steindal & Whitmore, 2019; Madrid et al., 2001;Zhdanova & Reebs, 2005); furthermore, even in the absence of any environmental cues, the biological clock autonomously oscillates with a circadian period (Zhdanova & Reebs, 2005). Fish can thus temporally ...
... When feed delivery is restricted to the same time every day, either under a light-dark cycle or under continuous light, fish synchronise their daily activities to this specific time period (López-Olmeda, Madrid et al., 2001;Zhdanova & Reebs, 2005). Thus, they can make temporal anticipation of feed delivery schedules, which often leads to increased locomotor activity before the forthcoming meal; this behaviour can be observed in group (Cañon Jones et al., 2012;Chapman et al., 2010;Reebs & Lague, 2000;Sánchez et al., 2009;Ferrari et al., 2016) or individually (Ali & Wootton, 2001;Holley et al., 2014). ...
While most animals have received increasing attention for their welfare, consideration for fish welfare has started more recently, particularly since the recognition that fish have emotions and complex cognitive abilities. Housing conditions in fish farms do not always meet fish ethological requirements as these conditions lack sufficient sensory and cognitive stimulations. An approach to address this issue involves enriching the rearing environment by including social, food, physical, or cognitive stimuli. Cognitive enrichment (CE) is a recent but promising concept to improve fish welfare by manipulating the predictability and controllability of their environment. It relies not only on the ability of fish to predict positive and negative events but also on their ability to perform and succeed in operant conditioning. In our present review, we identified four categories of CE: (i) feeding predictability, (ii) predictability of a negative event, (iii) operant conditioning through self-feeders, and (iv) learning experiences. Existing CEs were reviewed for their effects on behaviour, brain, zootechnical performances, and welfare in terms of physiological stress or physical integrity in the aquarium and farmed teleost fish. The review highlights unbalanced categories and the lack of adequate multidisciplinary analyses to assess the effects of these categories on fish welfare. Providing free access to self-feeders seems to be a good strategy, given its positive effects on zootechnical and physiological parameters. Other categories showed contradictory and species-dependent results; hence, further studies are required to confirm the benefits of CE on fish welfare. Finally, further investigations should also validate current CE systems and assess other strategies that may trigger positive emotions in fish.
https://authors.elsevier.com/c/1hDzQACeYFYfx
... Maintaining the circadian rhythm balance is significant for the growth, development, and immunity of fish (Zhdanova and Reebs 2005). A wide network of endogenous oscillators is known to control the circadian rhythm of vertebrates, and biological clock genes play different roles in regulating the duration of biological rhythms (Águeda et al. 2012;Herrero and Lepesant 2014). ...
... For instance, when the Syrian hamster was exposed to long photoperiod (LP) conditions, per1, per2, and per3 were found to be expressed for a longer period in the SCN, and the amplitude of the per1 peak was threefold higher than that of per3 in the pars tuberalis, suggesting that the expression of circadian pattern clock genes is sensitive to photoperiod variations (Tournier et al. 2003). Some studies have also shown that long-term photoadaptation also benefits the growth of teleost fish such as Nile tilapia (Zhdanova and Reebs 2005), meaning that fish possess unique mechanisms to adapt to long-term circadian rhythms. The light-dark (LD) cycle is the most reliable of these time cues and represents a powerful synchronizer of the central clock (Damiola et al. 2000;Stokkan et al. 2001). ...
Clock genes are essential for the daily functions of vertebrates and invertebrates and participate in a wide variety of biological functions including biochemical, physiological, and behavioral processes. Circadian clock disorders are detrimental to both humans and fish, and therefore research on the regulation of genes involved in the circadian clock has attracted increasing attention. Period 2 (per2) is an important gene whose expression is closely related to melatonin secretion, in addition to being affected by the photoperiod length. To gain more insights into the potential biological function of per2, we have cloned and expressed per2 in Amur minnow (Phoxinus lagowskii). We also analyzed melatonin content and AANAT2 gene expression under different short or long-term photoperiod conditions. In the present study, the secretion of melatonin in P. lagowskii was highest in the dark phase under short-term experiments. In the pituitary, the expression of the per2 gene was highest during the dark phase in both the 16L: 8D and 8L: 16D groups. The expression of the per2 gene in the brain was also highest during the dark phase in the 12L: 12D group. Though the expression of the per2 gene was not the highest in the dark phase for the other groups, there were no significant differences compared to the highest value. In addition, in the brain and pituitary, AANAT2 expression was highest during the light phase, except in the 8L: 16D group. Our findings suggested that Amper2 may participate in the feedback regulation of melatonin by regulating the expression of AANAT2. Fluorescence in situ hybridization analyses confirmed that per2 mRNA was expressed during the dark phase, especially in 16L: 8D group. Immunohistochemistry analyses confirmed that PER2 protein was expressed higher in 8L: 16D group. The dual luciferase experiment first validated the promotion of Wnt/β-Catenin expression by the per2 gene. Our results provide novel insights into the expression and location of per2, which contributes to a better understanding of the role of clock genes in the circadian rhythm and seasonal responses of high-latitude fish and might provide useful information of practical interest for high-latitude aquaculture.
... These biological rhythms are driven in part by external rhythms in the environment, such as the alternation of the light and dark phases, and photoperiod (duration of the light phase) (Kulczykowska et al., 2010;Kumar, 2017). Other parameters of the environment also play a synchronizing role, such as food intake, temperature and social interactions (Kulczykowska et al., 2010;Kumar, 2017;Zhdanova and Reebs, 2005). Daily rhythms (that have a 24-hour rhythm) are seen for many traits, including sleep cycle, immune system functions, glucose and lipid metabolism, as well as neurotransmitters and hormones secretion (Kumar, 2017). ...
Melatonin secretion follows a circadian pattern with a maximum level at night in many species. However, in zebrafish (Danio rerio, a diurnal fish species) large inter-individual variations in daily rhythmicity of melatonin levels are present and are associated with variation in behaviour. Melatonin secretion rhythm of proactive individuals that are more active and exploratory are of larger amplitude compared to reactive individuals. In threespine sticklebacks (Gasterosteus aculeatus), a nocturnal species, inter-individual variability of behaviour is well described. However, inter-individual variation of melatonin rhythm and its association with variation in behaviour has never been measured in this species, which would allow to test if patterns found in zebrafish can be generalized for diurnal and nocturnal species. We measured large inter-individual variation in melatonin levels and found that activity was positively correlated with plasma melatonin concentration measured at night. We did not observe any significant difference in nigh-day variation in melatonin concentration between very active and less active groups. However, we found that individuals classified as reactive based on their propensity to wall-hugging, a measure of anxiety in fish, showed large variation in melatonin between night and day, while this rhythm was not seen in proactive individuals that frequently used the center of the aquarium.Overall, our study suggests that melatonin may directly modulate behaviour in wild sticklebacks, and that while interindividual variation in melatonin rhythm may be widespread in fish, but with different pattern of variation depending on the species.
... In the present study, several genes, including arntl1a, clocka, arntl2, per2, and cry5, were involved in the circadian rhythm pathway, and all except cry5 increased as the temperature decreased. Studies of circadian rhythms in mammals and fish found that these genes formed a transcription-translation feedback loop: heterodimeric interactions of clock transcription factors (CLOCK (orthologous to fish clocka) and BMAL1 (ARNTL)) drive the transcription and translation of PERIOD1-3 (PER1-3) and CRYPTO-CHROME 1-2 (CRY1-2), which are translated into proteins and form heterodimers themselves, and are recycled from the cytoplasm back to the nucleus to inhibit BMAL1 and CLOCK (Cahill, 2002;Zhdanova and Reebs, 2006;Anea et al., 2018). Global loss of the BMAL1 or PER genes in this conserved transcription-translation feedback loop impairs vascular endothelial cell layer function, and has acute and chronic adverse effects on vascular system adaptation (Viswambharan et al., 2007;Somanath et al., 2011). ...
The tiger puffer ( Takifugu rubripes ) is an important economic fish species in northern China. However, it is a warm-temperature species, and low winter temperatures can result in high mortality in aquaculture. Understanding the mechanisms of cold resistance in tiger puffers will thus provide critical information to help cope with winter cold. In this study, we performed transcriptome analysis of livers from puffer fish kept at different temperatures (18°C, 13°C, and 8°C) to identify the key pathways and genes involved in the response to low-temperature stress. We also detected serum levels of proteases, arginine, and proline to obtain further information on the response to cold adaption. Totals of 51, 942, and 195 differentially expressed genes were identified in the 18°C vs 13°C, 18°C vs 8°C, and 13°C vs 8°C groups, respectively. Pathway analysis showed that significantly enriched pathways were mainly related to digestion, metabolism, and environmental adaptation. Most genes in the pathways related to digestion and metabolism were down-regulated, while most genes in the pathways related to environmental adaptation were up-regulated. Serum levels of proteases were significantly lower in the low-temperature groups (13°C and 8°C) compared with the control group (18°C), while arginine and proline levels were significantly higher in the 8°C group compared with the other two groups. These results suggest that low temperature caused digestive and metabolic disorders, as well as adaptive changes to low temperature in tiger puffers. On this premise, we found that some up-regulated genes in the pancreatic secretion pathway, arginine and proline metabolism pathway, and circadian rhythm pathway played important roles in the survival, growth, and development of tiger puffers under low-temperature stress. The accumulation of arginine and proline can maintain metabolism and circulation and resist cold stress. The circadian rhythm is closely related to digestion and metabolism, which is an adaptive change and plays a positive role in the resistance to low temperature. The results of this study provide new insights and a theoretical basis for the study of cold tolerance in tiger puffers.
... (b) Predicted average factorial scope for activity (FSA) for the six reef fish species across their body size range Furthermore, we quantified FSA assuming that fishes' spontaneous swimming activity follows strict circadian cycles, with all activity occurring diurnally. However, the activity patterns of reef fishes are often flexible(Zhdanova & Reebs, 2006). While, in principle, all our studied families are diurnally active, some species (e.g., Serranidae) can be nocturnally active(Mourier et al., 2016).Thus, our assumption can cause potential underestimates of FSA in C. argus and other species with more flexible circadian activity patterns. ...
Organismal metabolic rates (MRs) are the basis of energy and nutrient fluxes through ecosystems. In the marine realm, fishes are some of the most prominent consumers. However, their metabolic demand in the wild (field MR [FMR]) is poorly documented, because it is challenging to measure directly. Here, we introduce a novel approach to estimating the component of FMR associated with voluntary activity (i.e., the field active MR [AMRfield]). Our approach combines laboratory‐based respirometry, swimming speeds, and field‐based stereo‐video systems to estimate the activity of individuals. We exemplify our approach by focusing on six coral reef fish species, for which we quantified standard MR and maximum MR (SMR and MMR, respectively) in the laboratory, and body sizes and swimming speeds in the field. Based on the relationships between MR, body size, and swimming speeds, we estimate that the activity scope (i.e., the ratio between AMRfield and SMR) varies from 1.2 to 3.2 across species and body sizes. Furthermore, we illustrate that the scaling exponent for AMRfield varies across species and can substantially exceed the widely assumed value of 0.75 for SMR. Finally, by scaling organismal AMRfield estimates to the assemblage level, we show the potential effect of this variability on community metabolic demand. Our approach may improve our ability to estimate elemental fluxes mediated by a critically important group of aquatic animals through a non‐destructive, widely applicable technique. We know little about the metabolic demand of fishes in the wild. We propose a new approach to estimate active field metabolic rates by combining laboratory‐based respirometry and field‐based stereo‐video systems.
Photoperiod has a significant influence on fish. In this study, 2.5-year-old Takifugu rubripes (tiger puffer) adults were selected to evaluate the photoperiod impacts (8 h light (L):16 h dark (D), 12 L:12D, 16 L:8D) from September to January at 15–17 °C on their growth, gonadal development, and survival for a 100-day. The mortality rate of males and females tiger puffer differed among the different photoperiods, and the 8 L:16D photoperiod was not suitable for survival of males. At the end of the experiment, the body length, weight gain rate, specific growth rate and condition factor of both males and females tiger puffer were similar among the three photoperiods (P > 0.05). Higher percentage of females had developed to later developing phase and males had developed to spawning capable phase in the 12 L:12D treatment, respectively. In particular, 100% of males had testis at the spawning capable phase. The gonadosomatic index values of males and females in the 12 L:12D group were significantly higher than those in the 16 L:8D group (P < 0.05), but no significant differences between the 8 L:16D and 12 L:12D groups (P > 0.05). The serum testosterone (T) content of males and the serum estradiol-17β (E2) content of females were highest in the 12 L:12D group. The expression of aralkylamine N-acetyltransferase 1a (aanat1a) in the diencephalon/midbrain (D/M) was elevated under 12 L:12D treatment in both sex (P < 0.05). The expression level of iodothyronine deiodinase type 2 (dio2) in the saccus vasculosus in males was elevated under the 12 L:12D photoperiod (P < 0.05). The levels of gonadotropin-releasing hormone 1 (gnrh1) and gnrh3 mRNA in the D/M of females at later developing stages in the 12 L:12D treatment were significantly higher than those in of other treatment groups, and the level of gnrh3 in males under this photoperiod was significantly elevated (P < 0.05). The levels of gonadotropin-inhibiting hormone (gnih) mRNA under 12 L:12D were significantly elevated in both males and females (P < 0.05). Under this photoperiod, the levels of follicle stimulating hormone b-subunit (fshb) and luteinizing hormone b-subunit (lhb) in the pituitary gland of females at later developing stages were significantly higher than those of the other two groups (P < 0.05). The expression levels of lhb in males in the 12 L:12D and 8 L:16D photoperiods were significantly higher than that at 16 L:8D (P < 0.05). These results indicated that culture under the 12 L:12D photoperiod from September prior to the spawning season could result in accelerated gonadal development of both male and female tiger puffer.
La lumière exerce une influence majeure sur la physiologie et le comportement de la plupart des organismes. En particulier, elle synchronise les rythmes circadiens par un processus appelé photoentrainement. Chez les mammifères, le photoentrainement dépend de la rétine, et plus particulièrement d'une classe de cellules ganglionnaires de la rétine (RGCs) exprimant le photopigment mélanopsine (opn4). Ces RGCs sont intrinsèquement sensibles à la lumière bleue et sont appelés ipRGCs pour "intrinsically photosensitives RGCs". Les ipRGCs intègrent l'information lumineuse médiée par la mélanopsine avec celle provenant des photorécepteurs classiques pour contrôler le photoentrainement mais aussi le masking, un effet direct de suppression ou d'élévation de l'activité locomotrice par la lumière. Bien que les ipRGCs soient les médiateurs des effets circadiens et directs de la lumière sur le comportement des mammifères, leurs rôles chez les vertébrés non mammifères ne sont pas élucidés. Grâce à son développement externe rapide, à sa transparence et à sa capacité de manipulation génétique facile et d'analyse comportementale à haut débit, le poisson zèbre (PZ) est apparu comme un puissant modèle de vertébré diurne non mammifère pour la chronobiologie. Contrairement aux mammifères, la rétine n'est pas la seule structure photosensible chez le PZ. En particulier chez cette espèce, la glande pinéale contient des photorécepteurs et des neurones de projection (PNs, équivalent des RGCs) et peut donc recevoir une information lumineuse et la transmettre au cerveau. De plus, tous les organes adultes du PZ testés, y compris la glande pinéale, sont directement photoentraînables lorsqu'ils sont placés en culture. Il reste donc à déterminer quels sont les rôles respectifs de la photodétection périphérique (au niveau de tous les organes) et de la photodétection centrale (au niveau de structures spécialisées telles que la rétine et la glande pinéale) dans le photoentraînement. Nous nous sommes intéressé.e.s aux rôles des gènes de mélanopsine et des cellules les exprimant chez le PZ. Parmi les 5 gènes de mélanopsine présents chez cette espèce, opn4xa et opn4b sont exprimés dans les RGCs larvaires. De plus, nous avons montré qu'opn4xa est exprimé dans une sous-population de PNs. Ainsi, opn4xa définit une nouvelle population de PNs présentant une photosensibilité à la lumière bleue et verte dépendante d'opn4xa et qui fonctionne en mode LIGHT ON (Publications 1,2). Dans un second temps, nous avons cherché à comprendre la fonction des RGCs (opn4xa+ et opn4xa- - mutant lakritz -) et de la photosensibilité intrinsèque des RGCs et PN opn4xa+ (mutant opn4xa) dans l'influence directe et circadienne de la lumière sur l'activité locomotrice chez la larve de PZ. Nous avons trouvé que les RGCs sont impliqués dans le masking et la réponse locomotrice aux transitions lumineuses, mais indépendamment de la photosensibilité pilotée par opn4xa. Enfin, les mutants opn4xa-/-, lakritz-/- et opn4xa -/- ; lakritz -/- n'ont montré aucun défaut de photoentraînement à un pulse de lumière blanche administré au début de la nuit suggérant que la photodétection de la rétine (y compris celle des ipRGCs) et la photodétection pilotée par la mélanopsine opn4xa ne sont pas nécessaires au photoentraînement chez la larve de PZ (Publication 2). Ces résultats soulèvent des différences majeures dans le photoentrainement circadien chez les mammifères et le poisson zèbre.
Basic knowledge about the effect of light on fish in needed to improve their development, survival, and growth to increase aquaculture efficiency. In this study, the effects of light photoperiods (light (L): dark (D) = 12:12 and 16:8) and spectrum (full spectrum (W), blue (B) and yellow (Y)) on Takifugu rubripes larvaes were assessed from 20 to 80 days after hatching (dah). At 50 dah, the body length of larvae exposed to Y16:8 and B16:8 was significantly higher than that in the W16:8 group (P < 0.05). The wet weight of larvae reared under B16:8 was significantly higher than that under B12:12 (P < 0.05). The wet weight of larvae exposed to B12:12 was significantly higher than that in the W12:12, and the wet weight of larvae exposed to B16:8 was significantly higher than that of larvae exposed to W16:8 and Y16:8 (P < 0.05). At 80 dah, the body length and wet weight of larvae reared under 12:12 were significantly higher than those of larvae reared under 16:8 in the white and yellow LEDs groups (P < 0.05). Additionally, the biochemical composition of muscle were affected, the levels of DHA and EPA+DHA were significantly higher in the W16:8 and B16:8 groups, compared to the W12:12 and B12:12 groups, respectively (P < 0.05). Since light is the predominant signal for the entrainment of circadian oscillators and controls growth as a zeitgeber, the expression of arylalkylamine N-acetyltransferase 2 (annat2), crytochrome 2 (cry2), peroid1 (per1) and per3 in the brain were also been measured. The long photoperiod 16:8 delayed the acrophases of annat2, and blue light decreased the expression of cry2 and per3. These results provide the theoretical basis for using LED lights in aquaculture production of T. rubripes larvae.
1. The swimming activity of 6 specimens of the Pachon cave form of Astyanax mexicanus was tested with regard to its time control under various light-dark(LD)cycles and constant conditions, and it is compared to that of a river form.
2. In general, activity is entrainable by all applied LDs, but even if the amplitude of a forcing signal increases the signal energies are lower than in the river fish.
3. In case of entrainment the maximum values of surface activity correspond to the dark phases, those of bottom activity to the light phases of a LD. Flexible patterns -as often observed in the river form in the range of resonance about 24 h - are very seldom. Furthermore, disturbances of ten occur in the entrainment of one activity form, or one form runs arrhythmic while the other is still entrained.
4. The activity answers to changing environmental conditions are not as uniformly quick as in the river fish. But the system hardly needs a swing-in time to become entrained when a LD starts.
5. After transition from LD to DD (= constant darkness) the entrained rhythms disappear immediately.
6. In no LD with a period length differing from 24 h a circadian rhythm can be observed in addition to the entrained frequency.
7. These results show that the passive system of the river form has developped into an extremely passive one being unable to oscillate and thus has become simplified during regressive evolution. Concerning the circadian oscillator of the epigean ancestor, it was also subjected to regression, but it has not been completely lost. After a LD with a period length about 24 h the circadian oscillator is able to act as a stable system, clearly shown by the freerunning circadian rhythms of surface activity. But out of this range the oscillator is unable to control activity. In DD after all other LDs activity patterns are arrhythmic.
There is no information on whether the daily foraging movements of fish shoals are the result of chance, the collective will of all shoalmates, or the leadership of a few individuals. This study tested the latter possibility. Shoals of 12 golden shiners, Notemigonus crysoleucas, were trained to expect food around midday in one of the brightly lit corners of their tank. They displayed daily food-anticipatory activity by leaving the shady area of their tank and spending more and more time in the food corner up to the normal time of feeding. Past this normal time they remained in the shade, even on test days when no food was delivered. Most of these experienced individuals were then replaced by naïve ones. The resulting ratio of experienced:naïve fish could be 5:7, 3:9 or 1:11. On their own, naïve individuals would normally spend the whole day in the shade, but in all tests the experienced individual(s) were able to entrain these more numerous naïve fish out of the shade and into the brightly lit food corner at the right time of day. Entrainment was stronger in the 5:7 than in the 1:11 experiment. The test shoals never split up and were always led by the same fish, presumably the experienced individuals. These results indicate that in a strongly gregarious species, such as the golden shiner, a minority of informed individuals can lead a shoal to food, either through social facilitation of foraging movements or by eliciting following behaviour. Copyright 2000 The Association for the Study of Animal Behaviour.
We have previously shown that the testicular development of underyearling male masu salmon Oncorhynchus masou reared under a long photoperiod was accelerated by oral melatonin treatment (0.5mg melatonin/kg body weight/day), suggesting that melatonin mediates photoperiodic signaling. In this study, we further examined the effects of a disturbance in the plasma melatonin profile on gonadal development in underyearling male masu salmon by administering a higher dose of melatonin. Fish randomly selected in June were divided into two groups. They were reared under a light:dark (LD) cycle of 16:8 (lights on 04:00-20:00 hr) and fed with pellets sprayed with melatonin or vehicle twice a day at 08:30 and at 15:30 hr (7.5mg melatonin/kg body weight/day) until October. Fish were sampled on Day 0, 25, 60, 90 and 120. The plasma melatonin levels were high in the dark phase and low in the light phase in the control group, while they were constantly high with no significant change in the melatonin-treated group. Melatonin treatment had inhibitory effects on the gonadosomatic index and plasma testosterone levels. Pituitary salmon gonadotropin-releasing hormone content and luteinizing hormone content were significantly lower in the melatonin-treated group on Day 60 and 90, respectively. These results indicate that the plasma melatonin profile is important for mediating photoperiodic signals that regulate brain-pituitary-gonadal axis in underyearling precocious male masu salmon.
The influence of the eyes and pineal gland on locomotor activity rhythms of channel catfish, Ictalurus punctatus, and the extent to which varying light intensity altered these activity rhythms were evaluated. Locomotor activity was measured in normal, blinded, pinealectomized, and pinealectomized-blinded channel catfish exposed to a 12:12 light/dark photoperiod of decreasing light intensities (7,500, 175, and 0.7 lx). Normal, blinded, and pinealectomized fish exhibited nocturnal activity patterns which corresponded with the exogenous photoperiod. Fish without lateral eyes and pineal gland did not entrain to the photoperiod but had arrhythmic activity patterns. Neither treatment nor light intensity affected total locomotor activity. Blinding or pinealectomy decreased the level of dark-period activity at low light intensities, but the effect of light intensity was not observed in normal and pinealectomized-blinded fish. Normal and blinded fish under constant light or constant dark exhibited arrhythmic activity. The pineal gland functions as an extraretinal light receptor in channel catfish.
The behavior of an animal, as well as its related physiological processes, is often rhythmic. An event may take place only at a certain time of day or night or season or year corresponding to certain natural external cycles. These cycles may exert varying degrees of control; their influence may be total, with the entire response dependent on the continued presence of the stimulus, or they may act as a cue, initiating, terminating, or synchronizing a particular event which is basically internally controlled. Knowledge of the relation of the external cycle to the behavior of the animal is essential to understanding the harmony between organism and environment. It allows us to predict when and where certain events are most likely to occur as well as when an animal may be predisposed to respond to a particular stimulus. In this chapter we examine, quantitatively, daily and seasonal rhythms in swimming speed and schooling of a marine pelagic migrating species, the bluefish, Pomatomus saltatrix L., held under controlled laboratory conditions.
This chapter summarizes the evidence concerning physiological and behavioral rhythms in fish and discusses these in their appropriate context. The evidence for or against the endogenous nature of daily rhythms of activity in fish has been somewhat contradictory. The possibility of “innate timing mechanisms” and listing a “physiological clock” is one of the biological factors influencing migrations. The slow acceptance of the idea of innate timing mechanisms may also result from incorrectly placed emphasis concerning their ecological usefulness as mere daily regulators restricting certain activities to specific and appropriate times of day or night in the presence of strong periodic factors of the environment that could be sufficient to directly cause, or properly time, these activities. A more important role of the daily rhythms lies in their basic involvement in photoperiodic induction phenomena, photoperiodism. The chapter summarizes the available experimental evidence concerning rhythms in fish and relates these data to recently developed ideas and theories about biological rhythms in general. The chapter reviews the currently prevailing concepts concerning biological time measuring.