External and internal controls of lunar-related reproductive rhythms in fishes

Evidence that the woman's ovarian cycle is driven by an internal circamonthly timing system

The ovarian cycle has a well-established circa-monthly rhythm, but the mechanisms involved in its regularity are unknown. Is the rhythmicity driven by an endogenous clock-like timer or by other internal or external processes? Here, using two large epidemiological datasets (26,912 cycles from 2303 European women and 4786 cycles from 721 North American women), analyzed with time series and circular statistics, we find evidence that the rhythmic characteristics of the menstrual cycle are more likely to be explained by an endogenous clock-like driving mechanism than by any other internal or external process. We also show that the menstrual cycle is weakly but significantly influenced by the 29.5-day lunar cycle and that the phase alignment between the two cycles differs between the European and the North American populations. Given the need to find efficient treatments of subfertility in women, our results should be confirmed in larger populations, and chronobiological approaches to optimize the ovulatory cycle should be evaluated.

Does exposure to moonlight affect day/night changes in melatonin and metabolic parameters in Amazonian fish?

Lunar cycle modulates the rhythmic activity patterns of many animals, including fish. The effect of the moonlight cycle on daily melatonin and metabolic parameters was evaluated in matrinxã (Brycon amazonicus) subjected to external natural lighting. Eighty juvenile were distributed in 4 tanks of 1m3 (20 fish/tank) and divided into two groups. One group was exposed to the full moon and the other group to the new moon for 30 days, which corresponds to the duration of the lunar period. At the end of the lunar phase, 6 fish from each group were anesthetized to collect blood, tissue and eye samples at midday and midnight. The comparison between the light and dark periods revealed a significant increase in plasma and ocular melatonin in the last period. However, there was no significant difference for plasma melatonin between moons. Ocular melatonin presented higher concentrations during the new moon. Glucose, total proteins, cortisol, liver glutathione and gill lipid peroxidation were higher in the full moon compared to in the new moon. Plasma triglyceride was higher during the night for the full moon, and the opposite was found for the new moon. Total cholesterol values were higher at night regardless the moon phase. Glutathione in the gills and lipid peroxidation in the liver showed no significant differences. These results highlight the importance of considering both the day and lunar cycles for melatonin and metabolic parameters in species of commercial interest and susceptible to stressful situations in rearing conditions.

A community genomics approach to natural hybridization

Hybridization is a complicated, oft-misunderstood process. Once deemed unnatural and uncommon, hybridization is now recognized as ubiquitous among species. But hybridization rates within and among communities are poorly understood despite the relevance to ecology, evolution and conservation. To clarify, we examined hybridization across 75 freshwater fish communities within the Ozarks of the North American Interior Highlands (USA) by single nucleotide polymorphism (SNP) genotyping 33 species (N = 2865 individuals; double-digest restriction site-associated DNA sequencing (ddRAD)). We found evidence of hybridization (70 putative hybrids; 2.4% of individuals) among 18 species-pairs involving 73% (24/33) of study species, with the majority being concentrated within one family (Leuciscidae/minnows; 15 species; 66 hybrids). Interspecific genetic exchange-or introgression-was evident from 24 backcrossed individuals (10/18 species-pairs). Hybrids occurred within 42 of 75 communities (56%). Four selected environmental variables (species richness, protected area extent, precipitation (May and annually)) exhibited 73-78% accuracy in predicting hybrid occurrence via random forest classification. Our community-level assessment identified hybridization as spatially widespread and environmentally dependent (albeit predominantly within one diverse, omnipresent family). Our approach provides a more holistic survey of natural hybridization by testing a wide range of species-pairs, thus contrasting with more conventional evaluations.

Reproductive condition of the black-lip pearl oyster Pinctada margaritifera during the lunar phase

This study analyzed the relationship between the lunar phase and the reproductive cycle of Pinctada margaritifera inhabiting Weno Island, Chuuk Lagoon, Micronesia. We measured indicators of maturity (gonadosomatic index [GSI] and sexual maturation-related genes) and investigated changes in the gonadal maturity stages (GMS) of P. margaritifera over lunar cycle. GSI was higher around the full moon. GMS of P. margaritifera were classified as the early gametogenesis stage, ripe and spawning stage, and spent and degenerating stage. A large percentage of oysters was observed in the ripe and spawning stage at the first quarter moon in female and the full moon in male as well as in the spent and degenerating stages at the third quarter moon in both sexes. In addition, the expression of doublesex- and mab-3-related transcription factor 2 (DMRT2) in the male P. margaritifera black-lip pearl oyster was the highest during the full and third quarter moon phases, whereas no difference in expression was observed with the lunar phase in females. In contrast, the expression of vitellogenin (VTG) was the highest in female P. margaritifera during the first and third quarters. No difference in expression was observed according to the lunar phase in males. The results suggest that the lunar phase directly affects the expression of sexually mature gonads in P. margaritifera black-lip pearl oyster.

The evolution of monogamy in cichlids and marine reef fishes

Although several hypotheses have been proposed to explain the emergence of social monogamy, its origin is still intensely debated. Monogamy has many potential drivers, but evolutionary causality among them remains unclear. Using phylogenetic comparative methods within a Bayesian framework we explored the evolution of monogamy in cichlids and in marine reef fishes because, while both groups are characterised by unusually high incidence of social monogamy, they face very different ecological challenges. For each group, we examined four classic hypotheses that explain the evolution of monogamy: female dispersal, male mate guarding, female–female intolerance, and the biparental care hypotheses. We also explored whether the ecological traits of diet and shelter use are evolutionarily coupled with these hypotheses or with monogamy. First, we found that the evolution of monogamy was predicted by male territoriality in cichlids and simultaneous male and female territoriality in marine reef fishes. We suggest that these results provide support for the male mate guarding hypothesis in cichlids and female–female intolerance hypothesis in marine reef fishes. Second, we demonstrate clear evidence against the biparental care hypothesis, as biparental care was a consequence, not a cause, of monogamy in our analyses. Third, as female dispersal drove the loss of monogamy in both cichlids and marine reef fishes, this suggests the female dispersal hypothesis is not driving the evolution of monogamy in either group. These findings in two highly-monogamous fish taxa largely support prior findings from primate and bird comparative studies and provide novel large-scale evidence for a link between mate guarding and the evolution of monogamy.

Endogenous rhythm variation and adaptation to the tidal environment in the freshwater snail, Semisulcospira reiniana

Organisms have endogenous timekeeping system(s) to coordinate their biological processes with environmental cycles, allowing adaptation to external rhythmic changes in their environment. The change in endogenous rhythms could contribute to range expansion in a novel rhythmic environment. We hypothesized that populations of the freshwater snail near estuaries show a circatidal rhythm to synchronize with the tidal cycle. We compared the behavioral and gene expression rhythms between non-tidal and tidal populations of the freshwater snail, Semisulcospira reiniana. Individuals inhabiting tidal areas exhibited a rhythmic activity pattern coordinated with the tidal cycle under both field and laboratory conditions, but individuals inhabiting upstream non-tidal areas showed a circadian activity pattern. The proportion of circadian oscillating genes was greater in non-tidal than in tidal individuals, while that of circatidal oscillating genes was greater in tidal than in non-tidal individuals. Additionally, transcriptome-wide population genetic analyses revealed that these two adjacent populations can be clearly distinguished genetically, though the genetic distance was very small. Our results provide evidence of the shift in an endogenous rhythm via range expansion to a novel rhythmic environment. The changes in a small number of genes and/or phenotypic plasticity may contribute to the difference in the endogenous rhythms between non-tidal and tidal populations.

Tidal effects on periodical variations in the occurrence of singing humpback whales in coastal waters of Chichijima Island, Ogasawara, Japan

Marine organisms inhabiting coastal waters are known to be driven by periodic cycles such as diel, tidal, and seasonal changes. Humpback whales (Megaptera novaeangliae) breed in shallow and warm coastal waters, with males singing complex songs during the breeding season. To investigate periodic variations in humpback whale singing activities, we conducted fixed passive acoustic monitoring in the Ogasawara (Bonin) Islands, Japan, from winter to spring during 2016-2018. The singing activity and individual number of singers were observed throughout the day and night using a very long baseline passive acoustic array. The occurrence of singers peaked before sunrise and in the evening and was reduced during the daytime. The frequency of song reception depended on the tidal phase. A generalised additive model demonstrated that the occurrence of singers increased during the flood tide and decreased during the ebb tide in the waters west of Chichijima Island. These results suggest that the singing behaviour of humpback whales in breeding areas is affected by the diel and tidal cycles. Male humpback whales may change their behaviour or singing location depending on the strength and direction of the tidal current, considering that the selection of a stable location is beneficial for singing whales.

Lunar Cycle Influences Production of Tilapia (Oreochromis spp) Eggs in an Intensive Outdoor Production System in the Tropics

A robust body of evidence has demonstrated that the lunar cycle plays an important role in the reproduction of fish living in natural environments. However, little is known about the influence of the moon on tilapia reproductive activity in intensive fish farming systems. This study aims to evaluate the influence of the lunar cycle on the reproductive performance of tilapias in an intensive outdoor tropical production system in Latin America. Records of two tilapia strains (Nile tilapia [Oreochromis niloticus; n = 75] and Red tilapia [Oreochromis spp.; n = 1335]) reared in concrete tanks in a commercial fish farm were analyzed. Over a 3-year period, 60,136 captures were made in intervals of 12 to 14 days and 6,600 females were manually spawned. The number of females spawned and the volume of eggs collected from each tank (n = 9) were recorded. Data was analyzed by the general linear model and means were compared by least squares means method. A very slight or no variation was observed when the lunar cycle was split into two halves (crescent and waning). The proportions of females spawned and the volume of eggs per spawned female and per female in the tank varied considerably across the eight periods of the lunar cycle, with greater values in the waning than in the crescent phase. A significantly greater proportion of tilapia spawned and yielded more eggs around the full moon than around the new moon and remaining days of the lunar cycle. The moon cycle affected the reproductive activity of tilapia, which were more reproductively active around the full moon and most of the waning phase.

Multiyear trend in reproduction underpins interannual variation in gametogenic development of an Antarctic urchin

Ecosystems and their biota operate on cyclic rhythms, often entrained by predictable, small-scale changes in their natural environment. Recording and understanding these rhythms can detangle the effect of human induced shifts in the climate state from natural fluctuations. In this study, we assess long-term patterns of reproductive investment in the Antarctic sea urchin, Sterechinus neumayeri, in relation to changes in the environment to identify drivers of reproductive processes. Polar marine biota are sensitive to small changes in their environment and so serve as a barometer whose responses likely mirror effects that will be seen on a wider global scale in future climate change scenarios. Our results indicate that seasonal reproductive periodicity in the urchin is underpinned by a multiyear trend in reproductive investment beyond and in addition to, the previously reported 18-24 month gametogenic cycle. Our model provides evidence that annual reproductive investment could be regulated by an endogenous rhythm since environmental factors only accounted for a small proportion of the residual variation in gonad index. This research highlights a need for multiyear datasets and the combination of biological time series data with large-scale climate metrics that encapsulate multi-factorial climate state shifts, rather than using single explanatory variables to inform changes in biological processes.

Bioresilience to Mercury Chloride of the Brine Shrimp Artemia Salina after Treatment with Homeopathic Mercurius Corrosivus

INTRODUCTION

 Finding solutions to mitigate the impact of pollution on living systems is a matter of great interest. Homeopathic preparations of toxic substances have been described in the literature as attenuation factors for intoxication. Herein, an experimental study using Artemia salina and mercury chloride was developed as a model to identify aspects related to bioresilience.

AIMS

 The aim of the study was to describe the effects of homeopathic Mercurius corrosivus (MC) on Artemia salina cysts hatching and on mercury bioavailability.

METHODS

 Artemia salina cysts were exposed to 5.0 µg/mL of mercury chloride during the hatching phase. MC potencies (6cH, 30cH, and 200cH) were prepared in sterile purified water and poured into artificial sea water. Different controls were used (non-challenged cysts and challenged cysts treated with water, succussed water, and Ethilicum 1cH). Four series of nine experiments were performed to evaluate the percentage of cyst hatching. Soluble total mercury (THg) levels and precipitated mercury content were also evaluated. Solvatochromic dyes were used to check for eventual physicochemical markers of MC biological activity.

RESULTS

 Significant delay (p < 0.0001) in cyst hatching was observed only after treatment with MC 30cH, compared with controls. This result was associated with an increase of THg concentration in water (p = 0.0018) and of chlorine/oxygen ratio (p < 0.0001) in suspended micraggregates, suggesting changes in mercury bioavailability. A specific interaction of MC 30cH with the solvatochromic dye ET33 (p = 0.0017) was found.

CONCLUSION

 Changes in hatching rate and possible changes in Hg bioavailability are postulated as protective effects of MC 30cH on Artemia salina, by improving its natural bioresilience processes.

Opsins and gonadal circadian rhythm in the swordfish (Xiphias gladius) ovary: Their potential roles in puberty and reproductive seasonality

Circadian rhythm is well known to play a pivotal role in reproduction but the presence of a gonadal circadian rhythm is opening a lot of questions about a local regulation of reproduction. In the present study, we first set to identify the key genes driving circadian rhythmicity from the gonadal transcriptome of the swordfish, a commercially relevant species undergoing overfishing, and we then investigated whether their transcriptional activity was influenced by the maturation stage. Finally, we explored whether seasonality had the ability to modulate the expression of these genes. Interestingly, we identified a wide number of circadian rhythm related genes in the transcriptome of the swordfish gonad including, among the others, clock, bmal1, cry2 and per2, which have been found to be differentially expressed between sexually immature and mature individuals sampled during the breeding season. This differential modulation was also found for melatonin biosynthesis genes (mel1b, asmt and tph1) as well as opsin genes (opsin4, tmt opsin, parapinopsin, VA opsin, rho and sws), known to be the primary receptors of light stimuli. These differences were not observed between mature and immature individuals when considering the non-breeding season suggesting that, despite the molecular machinery of mature gonads is able to respond to signals driving ovarian maturation, these signals are not present hence highlighting the potential role of seasonality in modulating the gonadal circadian rhythm. These results confirm the presence of a gonadal circadian rhythm in the swordfish and open new interesting questions about its role in driving puberty onset.

Does estrogen regulate vitellogenin synthesis in corals?

Most broadcast spawner corals have a vitellogenic phase that lasts at least 6 months. It is established that estrogen regulates vitellogenin synthesis in vertebrates. Although some research have been conducted on the physiological role of sex steroids in corals, little is known about their involvement in oocyte development. This study aimed to detect steroid hormones - progesterone, testosterone, and estradiol-17β (E2) - in Acropora tenuis and study the relationships between vitellogenesis/vitellogenin synthesis and these steroids. This study also investigated the effect of E2 on vitellogenin synthesis in corals and identified steroidogenic enzymes in A. tenuis genome. Branches from tagged coral colonies were collected monthly from March to November. Histological observations showed that oocytes were vitellogenic from March to May (Stage IV and V), but not in June, and that gonads were occupied by immature oocytes in September (Stage I). Real-time qPCR revealed that vitellogenin (vg1 and vg2) transcript levels in coral branches were high in April and May, implying that corals actively underwent vitellogenesis during these months, and spawned before June. Liquid chromatography-mass spectrometry revealed that E2 could be detected in coral branches in March, April, and May, but not in June, whereas testosterone and progesterone did not fluctuate much in the same months. Immersing branches in E2-containing seawater failed to increase vitellogenin transcript levels. The results indicate that E2 is involved in oogenesis but does not positively regulate vitellogenin synthesis. Steroidogenic enzymes (except CYP19A) were identified in A. tenuis, suggesting that corals may endogenously synthesize progestogens and androgens from cholesterol.

Verification of differentially expressed genes in relation to hydrostatic pressure in the brain of two wrasse species with high-tide preference in spawning

Fish that inhabit shallow water are exposed to periodic changes in tidal cues, including hydrostatic pressure (HP). The present study aimed at verifying differentially expressed genes (DEGs) in the brain of the threespot wrasse Halichoeres trimaculatus (tropical species) and the honbera wrasse Halichoeres tenuispinis (temperate species), both of which were exposed to HP at 30 kPa (possible high-tide stimuli in the field) or 1 kPa (low tide) for 3 or 6 h. A de novo assembly yielded 174,710 contigs (63,530 contigs were annotated) from the brain of threespot wrasse. Following RNA sequencing, quantitative PCR confirmed DEGs that were upregulated [AT atypical cadherin 2 (FAT2)] and downregulated [neuronal leucine-rich repeat protein 3 (LRRN3), dual specificity tyrosine phosphorylation-regulated kinase 1 (DYRK), mitogen-activated protein kinase kinase 1 (MAP2K1) and phosphoinositide 3 kinase (PI3K)]. The effect of HP on the transcription of these DEGs (except for MAP2K1) disappeared within 6 h, suggesting that HP is a transitory stimulus occurring at the beginning of the tidal cycle. Similar DEG transcription was observed in the brain of honbera wrasse maintained under HP for 6 h. In situ hybridization of the brain of the threespot wrasse revealed that strong signals of MPA2K1 were seen in the telencephalon, diencephalon and pituitary, whereas those of PI3K were seen in the telencephalon, diencephalon and medulla oblongata. This result suggests that these kinases are involved in sensory function (telencephalon), somatic and visceral function (medullar oblongata) and the neuroendocrine system (diencephalon and pituitary), all of which were related to changes in HP stimuli. Following HP exposure, the transcription of c-fos increased in the pituitary of honbera wrasse, suggesting that external stimuli directly or indirectly activate hormone synthesis at the hypothalamic-pituitary-gonadal axis. It is concluded that HP alters gene expression in relation to neural development and function in the central nervous system and plays a role in exerting tidal-related reproduction and feeding in wrasses.

Moonlight is a key entrainer of lunar clock in the brain of the tropical grouper with full moon preference

Background

Many animals in coral reefs exhibit lunar cycles in their reproduction, showing synchronous gametogenesis and spawning at a particular moon phase. How these lunar reproductive cycles are endogenously regulated remains unknown, although changes in moonlight between the new moon and full moon are likely involved in this rhythmic event.

Results

This study evaluated the possible role of cryptochrome (cry1, cry2, cry3) in phase shifting and setting in the honeycomb grouper Epinephelus merra, which is a typical lunar spawner with full moon preference. qPCR analysis revealed that when fish were reared under alternating light-dark conditions, the transcript levels of cry1 and cry2, but not of cry3, in the diencephalon and pituitary gland showed daily variations. Weekly collection at midnight showed increases in the transcript levels of cry1 and cry2 in the diencephalon, but not the pituitary gland, from the first quarter moon through the last quarter moon. In comparison to the new moon, these transcript levels were significantly lower at all other sampling times. The artificial full moon conditions for 1 month resulted in increased cry transcript levels in both tissues at 2 (cry1) or 2 and 4 (cry2) weeks after the initiation of full moon conditions.

Conclusions

These results indicate the importance of transient changes in “brightness at night” in the response to moonlight for the phase shift and of “darkness at night” during the new moon for the phase set to the determined moon phase. We concluded that the moon phase-dependent oscillation of clock genes plays a role in lunar cycle-dependent behaviors in fish.

Molecular cloning of insulin-like growth factor 3 (igf3) and its expression in the tissues of a female damselfish, Chrysiptera cyanea, in relation to seasonal and food-manipulated reproduction

Food availability is a permissive determinant that drives gonadal activity in fish. The present study aimed to clarify the interactions between reproductive and nutritive statuses in the sapphire devil (Chrysiptera cyanea), a tropical damselfish with a long-day preference for reproduction. Insulin-like growth factor 3 (IGF3), a novel IGF that likely plays a role in gonadal maturation, was closely monitored in the sapphire devil. The cDNA of sapphire devil igf3 had an open reading frame of 443 base pairs (146 amino acid residues). Phylogenetic analyses revealed that sapphire devil IGF3 was clustered within the teleost IGF3 family. The transcript levels of sapphire devil igf3 increased in the brain, liver, and ovary of the fish during the late vitellogenic phase, suggesting that it plays a role in reproduction. Immersion of the fish in seawater containing estradiol-17β suppressed transcript levels of sapphire devil igf3 in the liver, but not in the brain, suggesting that intensive protein synthesis in relation to vitellogenesis negatively impacts somatic metabolism in this tissue. When fish were reared with high or low food under conditions of photoperiod (LD = 14:10) and temperature (at 25-28 °C) during the non-reproductive season, ovarian development was induced in high-food fish. Furthermore, prior to ovarian development in the high-food fish, the transcript levels of sapphire devil igf3 increased in the brain, liver, and ovary. These results indicated crosstalk between the reproductive and growth networks and suggested that a metabolic shift, from growth mode to reproductive mode, occurs in peripheral tissues when nutritive status is improved under suitable conditions of photoperiod and water temperature.

Can skyglow reduce nocturnal melatonin concentrations in Eurasian perch?

Artificial light at night (ALAN) changes the natural rhythm of light and darkness and can impair the biorhythms of animals, for example the nocturnal melatonin production of vertebrates, which serves as a proxy for daily physiological rhythms. Freshwater fish are exposed to ALAN in large urban and suburban areas in the form of direct light or in the form of skyglow, a diffuse brightening of the night sky through the scattered light reflected by clouds, atmospheric molecules, and particles in the air. However, investigations on the sensitivity of melatonin production of fish towards low intensities of ALAN in the range of typical skyglow are rare. Therefore, we exposed Eurasian perch (Perca fluviatilis) to nocturnal illumination levels of 0.01 lx, 0.1 lx and 1 lx and a control group with dark nights and daylight intensities of 2900 lx in all groups. After ten days of exposure to the experimental conditions, tank water was non-invasively sampled every 3 h over a 24 h period and melatonin was measured by ELISA. Melatonin was gradually reduced in all treatments with increasing intensity of ALAN whereas rhythmicity was maintained in all treatment groups although at 1 lx not all evaluated parameters confirmed rhythmicity. These results show a high sensitivity of Eurasian perch towards ALAN indicating that low light intensities of 0.01 lx and 0.1 lx as they occur in urban and suburban areas in the form of skyglow can affect the physiology of Eurasian perch. Furthermore, we highlight how this may impact perch in their sensitivity towards lunar rhythms and the role of skyglow for biorhythms of temperate freshwater fish.

Daily variation of D2 dopamine receptor transcription in the brain of the Japanese eel Anguilla japonica and its regulation with dopamine and melatonin

Dopamine plays a crucial role in controlling reproduction in eels, and its action is mediated through D2-type dopamine receptors. D2A and D2B receptors in the Japanese eel Anguilla japonica were cloned and characterized in the present study. Attention (daily expression patterns in the brain and endogenous regulation) was paid to D2B receptor because it is considered to play a crucial role in eel reproduction. The cDNAs of D2A and D2B receptors had open reading frames comprising 456 and 454 amino acid residues, respectively, which were phylogenetically clustered with those of other teleost species. Both receptors were highly expressed in the brain. D2B receptor transcript levels exhibited high day/low night variation in the midbrain and pituitary, suggesting that its transcription in these tissues is regulated in a daily manner, possibly under influence of melatonin. Intraperitoneal injection of dopamine downregulated D2B receptor transcription significantly in the midbrain and moderately in the pituitary within 1 h, but upregulated its transcription in the forebrain. Co-injection of dopamine with its antagonist (domperidone) reversed the effect of dopamine in the pituitary and forebrain, but not in the midbrain, suggesting that the effect of dopamine on D2B receptor transcription differs among brain regions. The same treatment with melatonin resulted in decreased D2B receptor transcription in the midbrain. These findings indicate that dopamine and melatonin have key roles in the daily variation in D2B receptor transcription in the brain of Japanese eel, and that they are related to a daily base secretion of hormones in the hypothalamic-pituitary-gonadal axis in this species.

Involvement of melatonin in transducing moon-related signals into the reproductive network of the female honeycomb grouper Epinephelus merra

Most groupers (genus Epinephelus) inhabiting tropical and subtropical waters exhibit lunar-related reproductive cycles. Their gametes develop synchronously toward and are released around the species-selected moon phase. Periodical changes in cues from the moon are likely used as zeitgeber, and the hypothalamic-pituitary-gonadal (HPG) axis may be activated after cues are perceived by the sensory organ and transduced as internal signals. The objective of this study was to examine weekly changes in mRNA expression profiles of gonadotropin-releasing hormones (gnrh1 and gnrh2) and the β-subunit of gonadotropins (fshβ and lhβ) during the spawning season (May to June) of the female honeycomb grouper Epinephelus merra, which spawns around the full moon period. When mature females were collected based on the lunar cycle, the gonadosomatic index peaked around the full moon. Ovarian histology revealed that oocytes laden with yolk developed toward the full moon and, subsequently, ovulatory follicles appeared around the last quarter moon, confirming lunar-related spawning with a full moon preference. Real-time quantitative polymerase chain reaction analyses revealed high abundances of fshβ and lhβ toward the first quarter moon, whereas concentrations of gnrh1 and gnrh2 increased around the last quarter moon and the first quarter moon, respectively, suggesting that transcription levels of these hormones fluctuate with the lunar cycle. The measurement of melatonin in the eye around the new moon and the full moon revealed that the ocular melatonin content was higher around the new moon than around the full moon, suggesting that the honeycomb grouper can perceive changes in moonlight. In addition, implantation of an osmotic pump containing melatonin into the body cavity of E. merra reduced the transcription levels of gonadotropins, suggesting that melatonin negatively affects hormonal synthesis at the HPG axis. We concluded that melatonin plays an essential role in transducing periodical changes in moonlight and that decreases in melatonin levels from the new moon to the full moon activate the HPG axis for entrainment of gonadal development and spawning.

Lunar influences in the diet habits and selectivity of larval clingfish Gobiesox marmoratus

The influence of the lunar cycle on the feeding habits, feeding success and selectivity was tested in situ on larval stages of the clingfish Gobiesox marmoratus (Gobiesocidae). Gobiesox marmoratus larvae and their prey were collected in the water column during the lunar cycle in austral spring 2015 and 2016, in shallow waters (<30 m depth) of El Quisco, central Chile. Feeding incidence was high (80-100%) throughout the moon cycle. The diet was composed of 32 prey items, being gastropod larvae and invertebrate eggs the most important. Prey composition varied among lunar phases with the lowest prey richness during new moon. During 2016, G. marmoratus larvae ingested the lowest number, but the largest prey during new moon. In spring 2015, there were no significant changes in the abundance of each prey taxon in the water column among moon phases, but in spring 2016 there were significant differences in the abundance of cypris and copepod nauplii, particularly between full and new moon. Feeding selectivity index showed that gastropod larvae were positively selected throughout the lunar cycle during spring 2015. In spring 2016, invertebrate eggs were selectively ingested in full moon and third quarter, but at a new moon G. marmoratus larvae selected gastropod larvae. Mean temperature of the water column and its vertical gradient and nocturnal cloud cover influences the feeding success of larval G. marmoratus. Lunar illumination favoured only an increase of richness of prey items. Therefore, nocturnal cloud cover precludes a greater influence of lunar illumination in the larval trophic ecology of this crypto-benthic fish.

Acoustic accelerometry reveals diel activity patterns in premigratory Port Jackson sharks

Distinguishing the factors that influence activity within a species advances understanding of their behavior and ecology. Continuous observation in the marine environment is not feasible but biotelemetry devices provide an opportunity for detailed analysis of movements and activity patterns. This study investigated the detail that calibration of accelerometers measuring root mean square (RMS) acceleration with video footage can add to understanding the activity patterns of male and female Port Jackson sharks (Heterodontus portusjacksoni) in a captive environment. Linear regression was used to relate RMS acceleration output to time-matched behavior captured on video to quantify diel activity patterns. To validate captive data, diel patterns from captive sharks were compared with diel movement data from free-ranging sharks using passive acoustic tracking. The RMS acceleration data showed captive sharks exhibited nocturnal diel patterns peaking during the late evening before midnight and decreasing before sunrise. Correlation analysis revealed that captive animals displayed similar activity patterns to free-ranging sharks. The timing of wild shark departures for migration in the late breeding season corresponded with elevated diel activity at night within the captive individuals, suggesting a form of migratory restlessness in captivity. By directly relating RMS acceleration output to activity level, we show that sex, time of day, and sex-specific seasonal behavior all influenced activity levels. This study contributes to a growing body of evidence that RMS acceleration data are a promising method to determine activity patterns of cryptic marine animals and can provide more detailed information when validated in captivity.

Effects of Different Light Spectra on the Oocyte Maturation in Grass Puffer Takifugu niphobles

In order to examine the effects of four different light spectra (white, red, green, and blue) on the oocyte maturation, the change of reproductive parameters, via brain-pituitary-gonad (BPG) axis in grass puffer, were investigated. After exposure four different light spectra for 7 weeks, the abundance of gonadotropin-releasing hormone (GnRH) mRNA which is a type of seabream (sbGnRH) and two different subunit of gonadotropin hormones mRNAs, follicle-stimulating hormone (fshβ) mRNA and luteinizing hormone (lhβ) mRNA, were analyzed in the brain and pituitary. Histological analysis showed that the mature oocyte ratio in the green spectrum was higher than other light spectra-exposed groups. Gonadosomatic index (GSI) and oocyte developmental stage were also investigated in the gonad based on histological observations. GSI value with the presence of yolk stage oocytes was significantly increased in the green spectrum-exposed group when compared to that of the other light-exposed groups (white, red, and blue) (p˂0.05). The abundances of sbGnRH mRNA and fshβ mRNA in the green spectrum-exposed group were also significant higher than those of the other light spectra-exposed groups (p˂0.05). These results indicate that the maturation of oocyte in grass puffer can be accelerated by exposure to the spectrum of green. To better understand the molecular mechanism for the maturation of oocyte in grass puffer, further study examining the relationship between oocyte development and its related genes is required.

Moonlight controls lunar-phase-dependency and regular oscillation of clock gene expressions in a lunar-synchronized spawner fish, Goldlined spinefoot

Goldlined spinefoot, Siganus guttatus, inhabits tropical and subtropical waters and synchronizes its spawning around the first quarter moon likely using an hourglass-like lunar timer. In previous studies, we have found that clock genes (Cryptochrome3 and Period1) could play the role of state variable in the diencephalon when determining the lunar phase for spawning. Here, we identified three Cry, two Per, two Clock, and two Bmal genes in S. guttatus and investigated their expression patterns in the diencephalon and pituitary gland. We further evaluated the effect on their expression patterns by daily interruptions of moonlight stimuli for 1 lunar cycle beginning at the new moon. It significantly modified the expression patterns in many of the examined clock(-related) genes including Cry3 in the diencephalon and/or pituitary gland. Acute interruptions of moonlight around the waxing gibbous moon upregulated nocturnal expressions of Cry1b and Cry2 in the diencephalon and pituitary gland, respectively, but did not affect expression levels of the other clock genes. These results highlighted the importance of repetitive moonlight illumination for stable or lunar-phase-specific daily expression of clock genes in the next lunar cycle that may be important for the lunar-phase-synchronized spawning on the next first quarter moon.

Patterns of biophonic periodicity on coral reefs in the Great Barrier Reef

The coral reefs surrounding Lizard Island in the Great Barrier Reef have a diverse soundscape that contains an array of bioacoustic phenomena, notably choruses produced by fishes. Six fish choruses identified around Lizard Island exhibited distinctive spatial and temporal patterns from 2014 to 2016. Several choruses displayed site fidelity, indicating that particular sites may represent important habitat for fish species, such as fish spawning aggregations sites. The choruses displayed a broad range of periodicities, from diel to annual, which provides new insights into the ecology of vocalising reef fish species and the surrounding ecosystem. All choruses were affected by one or more environmental variables including temperature and moonlight, the latter of which had a significant influence on the timing and received sound levels. These findings highlight the utility of passive acoustic tools for long-term monitoring and management of coral reefs, which is highly relevant in light of recent global disturbance events, particularly coral bleaching.

Coupling spectral analysis and hidden Markov models for the segmentation of behavioural patterns

BACKGROUND

Movement pattern variations are reflective of behavioural switches, likely associated with different life history traits in response to the animals' abiotic and biotic environment. Detecting these can provide rich information on the underlying processes driving animal movement patterns. However, extracting these signals from movement time series, requires tools that objectively extract, describe and quantify these behaviours. The inference of behavioural modes from movement patterns has been mainly addressed through hidden Markov models. Until now, the metrics implemented in these models did not allow to characterize cyclic patterns directly from the raw time series. To address these challenges, we developed an approach to i) extract new metrics of cyclic behaviours and activity levels from a time-frequency analysis of movement time series, ii) implement the spectral signatures of these cyclic patterns and activity levels into a HMM framework to identify and classify latent behavioural states.

RESULTS

To illustrate our approach, we applied it to 40 high-resolution European sea bass depth time series. Our results showed that the fish had different activity regimes, which were also associated (or not) with the spectral signature of different environmental cycles. Tidal rhythms were observed when animals tended to be less active and dived shallower. Conversely, animals exhibited a diurnal behaviour when more active and deeper in the water column. The different behaviours were well defined and occurred at similar periods throughout the annual cycle amongst individuals, suggesting these behaviours are likely related to seasonal functional behaviours (e.g. feeding, migrating and spawning).

CONCLUSIONS

The innovative aspects of our method lie within the combined use of powerful, but generic, mathematical tools (spectral analysis and hidden Markov Models) to extract complex behaviours from 1-D movement time series. It is fully automated which makes it suitable for analyzing large datasets. HMMs also offer the flexibility to include any additional variable in the segmentation process (e.g. environmental features, location coordinates). Thus, our method could be widely applied in the bio-logging community and contribute to prime issues in movement ecology (e.g. habitat requirements and selection, site fidelity and dispersal) that are crucial to inform mitigation, management and conservation strategies.

An Overview of Monthly Rhythms and Clocks

Organisms have evolved to cope with geophysical cycles of different period lengths. In this review, we focus on the adaptations of animals to the lunar cycle, specifically, on the occurrence of biological rhythms with monthly (circalunar) or semi-monthly (circasemilunar) period lengths. Systematic experimental investigation, starting in the early twentieth century, has allowed scientists to distinguish between mythological belief and scientific facts concerning the influence of the lunar cycle on animals. These studies revealed that marine animals of various taxa exhibit circalunar or circasemilunar reproductive rhythms. Some of these rely on endogenous oscillators (circalunar or circasemilunar clocks), whereas others are directly driven by external cues, such as the changes in nocturnal illuminance. We review current insight in the molecular and cellular mechanisms involved in circalunar rhythms, focusing on recent work in corals, annelid worms, midges, and fishes. In several of these model systems, the transcript levels of some core circadian clock genes are affected by both light and endogenous circalunar oscillations. How these and other molecular changes relate to the changes in physiology or behavior over the lunar cycle remains to be determined. We further review the possible relevance of circalunar rhythms for terrestrial species, with a particular focus on mammalian reproduction. Studies on circalunar rhythms of conception or birth rates extend to humans, where the lunar cycle was suggested to also affect sleep and mental health. While these reports remain controversial, factors like the increase in "light pollution" by artificial light might contribute to discrepancies between studies. We finally discuss the existence of circalunar oscillations in mammalian physiology. We speculate that these oscillations could be the remnant of ancient circalunar oscillators that were secondarily uncoupled from a natural entrainment mechanism, but still maintained relevance for structuring the timing of reproduction or physiology. The analysis and comparison of circalunar rhythms and clocks are currently challenging due to the heterogeneity of samples concerning species diversity, environmental conditions, and chronobiological conditions. We suggest that future research will benefit from the development of standardized experimental paradigms, and common principles for recording and reporting environmental conditions, especially light spectra and intensities.

Light- and circadian-controlled genes respond to a broad light spectrum in Puffer Fish-derived Fugu eye cells

Some cell lines retain intrinsic phototransduction pathways to control the expression of light-regulated genes such as the circadian clock gene. Here we investigated the photosensitivity of a Fugu eye, a cell line established from the eye of Takifugu rubripes, to examine whether such a photosensitive nature is present. Microarray analysis identified 15 genes that showed blue light-dependent change at the transcript level. We investigated temporal profiles of the light-induced genes, as well as Cry and Per, under light-dark, constant light (LL), and constant dark (DD) conditions by quantitative RT-PCR. Transcript levels of Per1a and Per3 genes showed circadian rhythmic changes under both LL and DD conditions, while those of Cry genes were controlled by light. All genes examined, including DNA-damage response genes and photolyase genes, were upregulated not only by blue light but also green and red light, implying the contribution of multiple photopigments. The present study is the first to identify a photosensitive clock cell line originating from a marine fish. These findings may help to characterize the molecular mechanisms underlying photic synchronization of the physiological states of fishes to not only daily light-dark cycles but also to various marine environmental cycles such as the lunar or semi-lunar cycle.

Subspecies delineation amid phenotypic, geographic and genetic discordance in a songbird

Understanding the processes that drive divergence within and among species is a long-standing goal in evolutionary biology. Traditional approaches to assessing differentiation rely on phenotypes to identify intra- and interspecific variation, but many species express subtle morphological gradients in which boundaries among forms are unclear. This intraspecific variation may be driven by differential adaptation to local conditions and may thereby reflect the evolutionary potential within a species. Here, we combine genetic and morphological data to evaluate intraspecific variation within the Nelson's (Ammodramus nelsoni) and salt marsh (Ammodramus caudacutus) sparrow complex, a group with populations that span considerable geographic distributions and a habitat gradient. We evaluated genetic structure among and within five putative subspecies of A. nelsoni and A. caudacutus using a reduced-representation sequencing approach to generate a panel of 1929 SNPs among 69 individuals. Although we detected morphological differences among some groups, individuals sorted along a continuous phenotypic gradient. In contrast, the genetic data identified three distinct clusters corresponding to populations that inhabit coastal salt marsh, interior freshwater marsh and coastal brackish-water marsh habitats. These patterns support the current species-level recognition but do not match the subspecies-level taxonomy within each species-a finding which may have important conservation implications. We identified loci exhibiting patterns of elevated divergence among and within these species, indicating a role for local selective pressures in driving patterns of differentiation across the complex. We conclude that this evidence for adaptive variation among subspecies warrants the consideration of evolutionary potential and genetic novelty when identifying conservation units for this group.

Increase in telencephalic dopamine and cerebellar norepinephrine contents by hydrostatic pressure in goldfish: the possible involvement in hydrostatic pressure-related locomotion

Fish are faced with a wide range of hydrostatic pressure (HP) in their natural habitats. Additionally, freshwater fish are occasionally exposed to rapid changes in HP due to heavy rainfall, flood and/or dam release. Accordingly, variations in HP are one of the most important environmental cues for fish. However, little information is available on how HP information is perceived and transmitted in the central nervous system of fish. The present study examined the effect of HP (water depth of 1.3 m) on the quantities of monoamines and their metabolites in the telencephalon, optic tectum, diencephalon, cerebellum (including partial mesencephalon) and vagal lobe (including medulla oblongata) of the goldfish, Carassius auratus, using high-performance liquid chromatography. HP affected monoamine and metabolite contents in restricted brain regions, including the telencephalon, cerebellum and vagal lobe. In particular, HP significantly increased the levels of dopamine (DA) in the telencephalon at 15 min and that of norepinephrine (NE) in the cerebellum at 30 min. In addition, HP also significantly increased locomotor activity at 15 and 30 min after HP treatment. It is possible that HP indirectly induces locomotion in goldfish via telencephalic DA and cerebellar NE neuronal activity.

Multispecies spawning sites for fishes on a low-latitude coral reef: spatial and temporal patterns

Spawning sites used by one or more species were located by intensively searching nearshore coral reefs of Kimbe Bay (New Britain, Papua New Guinea). Once identified, the spawning sites were surveyed repeatedly within fixed 5 m radius circular areas, for  > 2000 h of observations ranging from before dawn to after dusk spanning 190 days between July 2001 and May 2004. A total of 38 spawning sites were identified on the seven study reefs distributed at an average of one site every 60 m of reef edge. Pelagic spawning was observed in 41 fish species from six families. On three intensively studied reefs, all 17 spawning sites identified were used by at least three species, with a maximum of 30 different species observed spawning at a single site. Spawning was observed during every month of the study, on all days of the lunar month, at all states of the tide and at most hours of the day studied. Nevertheless, the majority of species were observed spawning on proportionately more days from December to April, on more days around the new moon and in association with higher tides. The strongest temporal association, however, was with species-specific diel spawning times spanning < 3 h for most species. While dawn spawning, afternoon spawning and dusk spawning species were differentiated, the time of spawning for the striated surgeonfish Ctenochaetus striatus also differed significantly among sites. The large number of species spawning at the same restricted locations during predictable times suggests that these sites are extremely important on this low-latitude coral reef.

Singing in the moonlight: dawn song performance of a diurnal bird varies with lunar phase

It is well established that the lunar cycle can affect the behaviour of nocturnal animals, but its potential to have a similar influence on diurnal species has received less research attention. Here, we demonstrate that the dawn song of a cooperative songbird, the white-browed sparrow weaver (Plocepasser mahali), varies with moon phase. When the moon was above the horizon at dawn, males began singing on average 10 min earlier, if there was a full moon compared with a new moon, resulting in a 67% mean increase in performance period and greater total song output. The lack of a difference between full and new moon dawns when the moon was below the horizon suggests that the observed effects were driven by light intensity, rather than driven by other factors associated with moon phase. Effects of the lunar cycle on twilight signalling behaviour have implications for both pure and applied animal communication research.

Impacts of moonlight on fish reproduction

The waxing and waning cycle of the moon is repeated at approximately 1-month intervals, and concomitant changes occur in the levels of moonlight and cueing signals detected by organisms on the earth. In the goldlined spinefoot Siganus guttatus, a spawner lunar-synchronized around the first quarter moon, periodic changes in moonlight are used to cue gonadal development and gamete release. Rearing of mature fish under artificial constant full moon and new moon conditions during the spawning season leads to disruption or delay of synchronous spawning around the predicted moon phase. Melatonin, an endogenous transducer of the environmental light/dark cycle, increases in the blood and in the pineal gland around the new moon period and decreases around the full moon period. In synchrony with melatonin fluctuation, melatonin receptor(s) mRNA abundance is higher during the new moon period than during the full moon. The melatonin/melatonin receptor system is likely affected by moonlight. Measurements of the expression patterns of clock genes in neural tissues demonstrate that Cryptochrome (Cry1 and Cry3) and Period (Per2) fluctuate with lunar periodicity, the former peaking in the medial part of the brain around the first quarter moon period, and the latter peaking in the pineal gland around the full moon. Some clock genes may respond to periodic changes in moon phase and appear to be involved in the generation of lunar-related rhythmicity in lunar spawners. Thus, some fish use moonlight-related periodicities as reliable information for synchronizing the timing of reproductive events.

Cloning and expression of melatonin receptors in the mudskipper Boleophthalmus pectinirostris: their role in synchronizing its semilunar spawning rhythm

The mudskipper Boleophthalmus pectinirostris, a burrow-dwelling fish inhabiting intertidal mudflats, spawns only once during the spawning season around either the first or last lunar quarters. To understand the molecular mechanisms regulating this semilunar spawning rhythm, we cloned all melatonin receptor subtypes (mtnr1a1.4, mtnr1a1.7, mtnr1b, and mtnr1c). Expression of three melatonin receptor subtypes (except mtnr1c) was found in the ovaries. In contrast, the expression of all receptor subtypes was found in the diencephalon and the pituitary. In the fully-grown follicles, only mtnr1a1.7 mRNA was detected in both the isolated follicle layers and denuded oocytes. Interestingly, the transcript levels of both mtnr1a1.4 in the diencephalon and mtnr1a1.7 in the ovary displayed two cycles within one lunar month, and peaked around the first and last lunar quarters. We used 17α,20β-dihydroxy-4-pregnen-3-one (DHP), a maturation-inducing hormone, as a biomarker to examine the involvement of melatonin receptors in the control of the spawning cycle. Melatonin significantly increased the plasma DHP level 1h post intraperitoneal injection. Melatonin also directly stimulated ovarian fragments in vitro to produce a significantly higher amount of DHP. Taken together, these results provided the first evidence that melatonin receptors were involved in the synchronization of the semilunar spawning rhythm in the female mudskipper by acting through the HPG axis and/or directly on ovarian tissues to stimulate the production of DHP.

Influence of moonlight on mRNA expression patterns of melatonin receptor subtypes in the pineal organ of a tropical fish

The goldlined spinefoot, Siganus guttatus, is a lunar-synchronized spawner, which repeatedly releases gametes around the first quarter moon during the reproductive season. A previous study reported that manipulating moonlight brightness at night disrupted synchronized spawning, suggesting involvement of this natural light source in lunar synchronization. The present study examined whether the mRNA expression pattern of melatonin receptor subtypes MT1 and Mel1c in the pineal organ of the goldlined spinefoot is related to moonlight. Real-time quantitative polymerase chain reaction analysis revealed that the abundance of MT1 and Mel1c mRNA at midnight increased during the new moon phase and decreased during the full moon phase. Exposing fish to moonlight intensity during the full moon period resulted in a decrease in Mel1c mRNA abundance within 1h. Fluctuations in the melatonin receptor genes according to changes in the moon phase agreed with those of melatonin levels in the blood. These results indicate that periodic changes in cues from the moon influence melatonin receptor mRNA expression levels. The melatonin-melatonin receptor system may play a role in predicting the moon phase through changes in night brightness.

Moonlight affects mRNA abundance of arylalkylamine N-acetyltransferase in the retina of a lunar-synchronized spawner, the goldlined spinefoot

Melatonin synthesis in the pineal gland and retina shows a rhythmic fashion with high levels at night and is controlled by a rate-limiting enzyme, arylalkylamine N-acetyltransferase (AANAT). A previous study revealed that moonlight suppresses the plasma melatonin levels of the goldlined spinefoot (Siganus guttatus), which exhibits a lunar cycle in its reproductive activity and repeats gonadal development toward and spawning around the first quarter moon. Whether the retina of this species responds to moonlight is unknown. To clarify the photoperceptive ability of this species, we aimed to clone the full-length cDNA of Aanat1 (sgAanat1) from the retina and examine its transcriptional pattern under several daylight and moonlight regimes. The full-length sgAanat1 cDNA (1,038 bp) contained a reading frame encoding a protein of 225 amino acids, which was highly homologous to AANAT1 of other teleosts. Reverse transcription-polymerase chain reaction (PCR) analysis revealed that among the tissues tested, sgAanat1 fragments were expressed exclusively in the retina. Real-time quantitative PCR analysis revealed that sgAanat1 fluctuated with high abundance at night under light-dark cycle and at subjective night under constant darkness, but not under constant light. These results suggest that sgAanat1 is regulated by both the external light signal and internal clock system. The abundance of sgAanat1 in the retina was higher at the culmination time around new moon than full moon phase. Additionally, exposing fish to brightness around the full moon period suppressed sgAanat1 mRNA abundance. Thus, moonlight is perceived by fish and has an impact on melatonin fluctuation in the retina.

Lunar-rhythmic molting in laboratory populations of the noble crayfish Astacus astacus (Crustacea, Astacidea): an experimental analysis

Juvenile noble crayfish, Astacusastacus (Crustacea, Astacidea) in the second year of age were kept in the laboratory for a twelve-month period under continuing "summer conditions" (LD 16:8, 19°C). Molting processes in this population could be synchronized by artificial moonlight cycles. Peaks of exuviations occurred at "new moons". Males showed a slightly higher degree of synchronization than females. A phase-shift of the artificial lunar cycle in relation to the natural cycle resulted in a corresponding shift of the molting cycle. This clearly demonstrates that changes in the nocturnal light regime provide the primary external information for the lunar-monthly molting rhythm. There is a first indication that lunar photic stimuli do not act directly but as a zeitgeber which entrains an endogenous molting rhythm to the lunar cycle. Moreover, the results of the long-term experiments suggest that the hibernal resting period of A. astacus in the field (no molts between October and April) may also involve some endogenous programming. Continuing artificial summer conditions can delay but not completely suppress this resting period. The adaptive significance of the phenomena and how the findings may be applied to improve the management of crowded crayfish stocks are discussed.

Moon phase influences the diet of southern Ray's bream Brama australis

Diet composition of the southern Ray's bream Brama australis was examined from stomach contents of 399 specimens sampled by bottom trawl on Chatham Rise to the east of South Island, New Zealand, over 3 years. Prey items were predominantly mesopelagic fishes and crustaceans. Multivariate analysis indicated that moon phase explained more of the diet variability than any other predictor examined. It appears likely that diet composition is influenced by a combination of changes in both tidal flows and illumination. Different combinations of prey were consumed by B. australis at different times of the lunar cycle. An influence of moon phase on feeding by fishes has rarely been reported, but it is likely that moon phase influences the diets of other species that specialize in mesopelagic prey. The most important prey group by mass for B. australis was Myctophidae (primarily Lampanyctodes hectoris), followed by Stomiiformes (primarily Maurolicus australis) and shrimps (Sergestes spp). An ontogenetic shift in diet was observed, from numerical dominance by small crustaceans including amphipods and euphausiids (with some fishes) in smaller (mass <1045 g) B. australis to pelagic teleost prey (with a few larger crustaceans) in larger (>1440 g) B. australis.

Reproductive periodicity of the sparid, Acanthopagrus pacificus, on a hierarchy of temporal scales

The reproductive periodicity of the sparid, Acanthopagrus pacificus, over four temporal scales is described. Acanthopagrus pacificus had a short spawning season between June and September, and within this, a peak reproductive period from July to early September. During the peak period there were several spawning peaks corresponding to a lunar periodicity, with intense reproductive activity on new and full moons that peaked during the period of the full moon when the tidal range was greatest. At the smallest temporal scale, spawning occurred at night on ebb tides. Because this study draws on data collected in 1991 and 1995, it provides a useful baseline against which to judge future changes in reproductive periodicity.

The lunar cycle determines availability of coral-reef fishes at fish markets

During 139 visits between March 2009 and May 2011, it was found that the availability of reef fishes at a local fish market in the Philippines was highly affected by the lunar cycle. The number of vendors selling reef fishes was significantly lower (13.4%) during third lunar quarters (full moon periods) than during the first, second and fourth lunar quarters (40.2, 25.0 and 30.0%, respectively). It is recommended that the influence of the lunar cycle on fish availability is considered when designing sampling strategies for catch surveys.

Effects of hydrostatic pressure on monoaminergic activity in the brain of a tropical wrasse, Halicoeres trimaculatus: possible implication for controlling tidal-related reproductive activity

Most wrasse species in tropical waters exhibit daily spawning synchrony with a preference for high tide. Fish perceive tidal rhythm cues through sensory organs and activate the brain-pituitary-gonadal endocrine axis for synchronous gonadal maturation, although how the tidal-related spawning cycle is controlled endogenously is not known. The purpose of this study was to examine whether hydrostatic pressure has an impact on brain monoamine levels and reproductive activities in the threespot wrasse Halichoeres trimaculatus. The contents of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), serotonin (5-HT), and 5-hydroxyindoleacetic acid (5-HIAA) in the brain were measured using high-performance liquid chromatography and an electrochemical detection system. Exposing the fish to hydrostatic pressure occurring at a 3-m depth (~30 kPa) resulted in an increase in 5-HIAA/5-HT over 3h and a decrease in DOPAC/DA over 6h. No changes in gonadosomatic index or oocyte diameter were observed between the groups when female fish were reared at 0-m and 3-m depth for 3h. Hydrostatic pressure did not alter pituitary mRNA abundance of follicle stimulating hormone-β or luteinizing hormone-β. However, in vitro culture of ovaries from pressurized fish in the presence of human chorionic gonadotropin resulted in an increase in 17α,20β-dihydroxy-4-pregnen-3-one in the medium. These results suggest that hydrostatic pressure activates oocyte maturation through brain monoaminergic activity in this tropical wrasse species.