Apparent semi-lunar spawning rhythmicity in a brackish cardinalfish

The purpose of the present study was to examine the lunar-related spawning rhythmicity of the amboina cardinalfish Apogon amboinensis, which is a euryhaline species inhabiting mangrove creeks in the Indo-Pacific area. During the reproductive season, the gonado-somatic index increased towards and peaked within a week of the first and last quarter moon. Histological observations of the ovaries also showed development of yolk-laden oocytes towards the first and last quarter moon; postovulatory follicles, an indicator of spawning, appeared around these lunar phases. Fish with immature oocytes in the ovary were also collected in the same lunar phases, suggesting that at least two fish populations with different oocyte development stages exist at any given time. The levels of two steroid hormones secreted from the ovarian pieces into a culture medium with human chorionic gonadotropin were measured using enzyme-linked immunosorbent assay (ELISA). The level of oestradiol-17β increased around the new and full moon periods. On the other hand, 17α,20β-dihydroxy-4-pregnen-3-one levels increased around the first and last quarter moon, suggesting that the fish are actively undergoing vitellogenesis and final oocyte maturation around the respective lunar phase. These results suggest that with the 1 month ovarian development process, A . amboinensis exhibits a semi-lunar spawning pattern with peaks around the first and last quarter moon. When A . amboinensis were reared under laboratory conditions without the tidal stimuli, mouth-brooding was initiated in 13 of 20 males within a week of the first and last quarter moon. The possibility of a lunar-related endogenous rhythm in A . amboinensis is discussed.     

Sexual reproduction of Acropora reef corals at Moorea, French Polynesia

Little information is available on reproductive processes among corals in isolated central Pacific reef regions, including French Polynesia. This study examined the timing and mode of sexual reproduction for Acropora reef corals at Moorea. Spawning was observed and/or inferred in 110 Acropora colonies, representing 12 species, following full moon periods in September through November 2002. Gamete release was observed and inferred in four species of Acropora between 9 and 13 nights after the full moon (nAFM) in September 2002. Twelve Acropora spp. spawned gametes between 5 and 10 nAFM in October 2002, with six species spawning 7 nAFM and four species spawning 9 nAFM. In November 2002, spawning of egg and sperm bundles was observed and inferred in 27 colonies of Acropora austera, 6 nAFM. These are the first detailed records of spawning by Acropora corals in French Polynesia.     

Reproductive life history of the introduced peacock grouper Cephalopholis argus in Hawaii

This research investigated the reproductive biology (sex ratio, hermaphroditic pattern, size and age at maturity) of Cephalopholis argus, known locally in Hawaii by its Tahitian name roi. The results suggest that C. argus exhibits monandric protogyny (female gonad differentiation with female to male sex change) with females reaching sexual maturity at 1.2 years (95% c.i .: 0.6, 1.6) and 20.0 cm total length (L_T; 95% c.i .: 19.6, 21.2). The female to male sex ratio was 3.9:1. The average age and L_T at sex change was 11.5 years (95% c.i .: 11.1, 12.9) and 39.9 cm (95% c.i .: 39.5, 41.2), respectively. Current information on spawning seasonality of this species is incomplete, but based on the occurrence of spawning capable and actively spawning females, spawning probably takes place from May to October. Evidence of lunar spawning periodicity was found, with an increased proportion of spawning capable and actively spawning females, and an increased female gonado‐somatic index during first quarter and full‐moon phases. This information fills a valuable information gap in Hawaii and across the species' native range.     

Reproductive characteristics and gamete development of the soft coral Sclerophytum cf. heterospiculatum in Okinawa Island,Japan

Sexual reproduction data are important to understand how organisms can replenish their populations and proliferate on coral reefs. Despite the importance of such data, the reproductive characteristics of most soft coral species are still unknown. Here, we examined the reproductive strategies of a species from the often-dominant genus Sclerophytum in a coral reef on subtropical Okinawa Island, Japan. DNA barcoding and histological examinations of the tissues were conducted to confirm colony conspecificity and identify reproductive characteristics, respectively, between March 2020 and March 2021. Results indicated that the studied species, identified as Sclerophytum cf. heterospiculatum, exhibits gonochorism with longer oogenesis and shorter spermatogenesis. Female colonies produced immature oocytes throughout the year, with mature oocytes observed from late July to early September, and thus, extended spawning is likely characteristic of this species. In male colonies, spermatogenesis took place over ~5 months, with spermaries present from April through August. Mature spermaries were noted beginning in July and the inferred peak of sperm release was between late August and early September, which suggests that spermatogenesis duration was ~5 months. The largest mean oocyte and spermary sizes (628.45 ± 61.36 and 240.04 ± 49.49 μm, respectively) were both recorded in August. Gamete spawning presumably occurred during the summer season, which suggests seasonality in reproduction as influenced by changes in seawater temperature. However, the proximate cue for exact dates of spawning could be the lunar period because the inferred release of spawning materials seemed to occur between full moon and last-quarter moon phases in both the months of August and September. The results of this study represent the first detailed report of reproductive characteristics of the genus Sclerophytum in Japan.     

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.     

Lunar synchronization of the monthly reproductive rhythm in the sea urchin Centrostephanus coronatus Verrill

The monthly reproductive rhythm in the diadematid sea urchin Centrostephanus coronatus Verrill at Santa Catalina Island, California, was studied in the summer of 1973 and the results are compared with data for the summer of 1969. In the summer of 1973 the more extreme spring tides coincided with the new moon, while in the summer of 1969 the more extreme spring tides coincided with the full moon. The reproductive rhythm in both years was closely synchronized with lunar phases and not with the monthly tidal cycles; spawning occurred near the third lunar quarter in both years. These observations suggest that this monthly reproductive rhythm is synchronized by monthly changes in moonlight, and not by monthly tidal changes.     

Reproductive Ecology of Pterapogon kauderni, an Endemic Apogonid from Indonesia with Direct Development

Pterapogon kauderni does not have secondary sexual dimorphism, and has an equal sex ratio (50.8% males:49.2% females). Females first mature at a length of about 34mm. Data from both laboratory-bred and wild-collected eggs and embryos are not consistent with the presence of differential reproductive allocation in this species. Analysis from clutches brooded by wild-collected males shows a significant intra-clutch and among-clutch variation in egg size. Mean individual egg size (diameter, volume, or weight) is not correlated with the size (standard length, head length, or lower jaw length) of the males brooding those eggs. P. kauderni has a lunar reproductive cycle, with a major spawning peak during full moon and a smaller peak during the last quarter. Similarly, it has a major juvenile release (settlement) peak at full moon, with a minor peak at new moon. However, one population, which is located in a site with distinct environmental conditions and which was sampled a year earlier, shows a different reproductive pattern, last quarter being the phase where most of spawn and release events take place.     

Pair formation in the herbivorous rabbitfish Siganus doliatus

This study investigated the basis of pair formation in the abundant herbivorous rabbitfish Siganus doliatus on Orpheus Island, Great Barrier Reef. Pair formation was the most common social system in S. doliatus, with 67·4% of all individuals occurring in pairs. Pairs were stable (i.e. individuals remained with the same partner throughout the study) and pair members were found within 5 m of each other 82·9% of the time. Of the examined pairs, 25% were homosexual resulting in a proportion of heterosexual pairs (75%) that was significantly lower than expected if pairs were formed solely for reproductive reasons. Therefore, although reproduction appears to be the main driver of pair formation in S. doliatus, other factors are likely to influence this behaviour. The high density of individuals on the reef crest (5·7 ± 0·9 individuals 200 m^?2; mean ± s.e .) and extensively overlapping home ranges of pairs indicated that the defence of territories plays no role in pair formation. Instead, it appears that pair formation in S. doliatus is driven, in part, by other, non‐reproductive, ecological factors. It is suggested that pair formation allows for increased vigilance against predation and enables S. doliatus to execute a novel feeding behaviour.     

Physiological effects of the lunar cycle on the spawning of a coral reef fish,Abudefduf Vaigiensis: in vivo and in vitro trait

The aim of the present study was to investigate the lunar cycle effects of the spawning of Audefduf vaigiensis through in vivo and in vitro analysis. For this purpose, the indices of GSI, serum levels of sex steroids, including testosterone (T), 17α-hydroxyprogesterone (OHP), 17α, 20β-dihydroxyprogesterone (DHP), and 11-keto-testosterone (11-KT) as well as the germinal vesicle breakdown (GVBD) were measured. The sampling pattern was weekly, based on the moon cycles as the new moon (NM), the first quarter (FQ), the full moon (FM), and the last quarter (LQ). In females, the highest in vivo values of the GSI index were obtained in FQ and LQ, and in males, this value was significantly higher in LQ than NM. The highest in vivo level of OHP in females was observed in FQ, whereas in males was obtained in FM. In both sexes, the in vivo serum levels of DHP were obtained in LQ. In males, the level of 11-KT were at the peak in NM. In vitro analysis showed the highest rate of GVBD in LQ. Moreover, the in vitro levels of T, OHP, and DHP were significantly higher in LQ compare to NM in both sexes. However, in males, the in vitro levels of 11-KT was significantly higher in NM than LQ. These cyclical changes obtained from in vivo plasma steroid hormones and in vitro data on GVBD suggested that lunar periodicity is a major external regulator that synchronized ovarian and testicular activity of A. vaigiensis with emphasis on spawning phenomenon.

     

Reproductive activity in the checkered snapper, Lutjanus decussatus, off Ishigaki Island, Okinawa

The checkered snapper, Lutjanus decussatus, is an important species for fisheries in the Okinawan region. This study estimated the reproduction of this lutjanid species in the waters around Ishigaki Island. The main spawning season was estimated to be between June and October, since oocytes at the maturation stage and/or postovulatory follicles were found during the study period. In the main spawning season, high gonadosomatic index values were found around the time of the last quarter moon for each month from June to September. It is suggested that L. decussatus is a lunar-synchronized spawner off Ishigaki Island.     

Perception and possible utilization of moonlight intensity for reproductive activities in a lunar-synchronized spawner, the golden rabbitfish

Rabbitfishes are known to spawn synchronously around the species-specific lunar phase. It is considered that they perceive and utilize cues from the moon in order to be synchronized gonadal development and spawning with the lunar cycle. Using the golden rabbitfish, Siganus guttatus, which spawns synchronously around the first quarter moon during the reproductive season, we measured the fluctuation of melatonin levels and examined the response of the fish to moonlight intensity. Daily fluctuation of melatonin concentration in the blood of golden rabbitfish showed low levels during daytime and high levels during night-time, suggesting that melatonin functions in the perception and utilization of photoperiod. Plasma melatonin concentration at the new moon was higher than that at the full moon. When the fish were exposed to moonlight at midnight of the both moon phases, the melatonin concentrations decreased to the control levels. These results show that the fish possibly perceive moonlight intensity and plasma melatonin fluctuates according to 'lightness' at a point of night. At the first spawning period (experiment was started one month before the spawning), the fish reared under natural conditions spawned at the expected spawning dates, whereas the fish reared under the constant darkness and lightness of night did not spawn. At the second spawning period (experiment was started 2 weeks before the spawning), the fish reared under the conditions of natural and constant darkness of night spawned but not that of constant lightness of night. It is possible that night conditions are related to synchronous gonadal development and spawning in the golden rabbitfish.     

Moonlighting? - Consequences of lunar cues on anuran reproductive activity

While the influence of environmental variables, particularly temperature and rainfall, on the breeding behavior of amphibians is widely recognized, relatively few studies have addressed how the moon affects amphibian behavior. Yet, the lunar cycle provides several rhythmic temporal cues that animals could use to time important group events such as spawning, and the substantial changes in light levels associated with the different moon phases may also affect the behavior of nocturnal frogs. Using seven years of field observation data, we tested for lunar effects on the reproductive activity of male and female Eastern Gray Treefrogs (Hyla versicolor). We found that chorusing and breeding activity was statistically more likely to occur around the first quarter of the moon and during intermediately bright nights, but that reproductive activity also occurred during various other times during the lunar cycle. We discuss these findings in relation to the two main hypotheses of lunar effects on animals: predator avoidance and temporal synchronization of breeding.     

Release of planula larvae, settlement and development of Siderastrea stellata Verrill, 1868 (Anthozoa, Scleractinia)

We herein provide the first observations on planulation, larval development, and metamorphosis of Siderastrea stellata, an endemic reef-building species that occurs along the northeastern and southeastern coasts of Brazil. The release and settlement of larvae were observed in two distinct periods. The first started 3 days after collection on January 28 during the last quarter, whereas the second started 2 months later, on April 10 during the change from new moon to the first quarter. Planulation continued throughout approximately 48 h. Brooded larvae released from the mouth contained zooxanthellae, and underwent settlement after 48 h. Newly extruded larvae stayed in close contact with parental polyps. Fusion was observed among larvae from the same colony. The first septal cycle was formed by day 2–3, while the third cycle of exosepta became evident 15 days after protosepta development. The development of the corallite of primary polyp was slow, and after 9 months of analyses no evidence of budding was obtained, this indicating that colonial development is likely to be a late event in the S. stellata life history.     

Lunar-related reproductive behaviour in the badger (Meles meles)

Cyclicity in behaviours, including reproduction, in relation to the lunar cycle is widely documented in some phyla, but weak or unknown in Class Mammalia. In this paper we present long-term video surveillance data of wild Eurasian badgers Meles meles, which reveal a strong correlation between reproductive behaviour and the lunar cycle. Squat marking and raised-leg urination, which increase in frequency at times of reproductive activity, showed maxima around day 22 of the lunar cycle (i.e. new moon). These findings were supported by observations of matings, together with published records, which showed significantly higher occurrence in the lunar dark phase (last quarter to first quarter). We propose that the lunar cycle has the potential to act as a regulator of the reproductive cycle in the badger.     

Reproductive Cycle and Developmental Processes During Embryogenesis of Clavularia hamra (Cnidaria,Octocorallia)

Clavularia hamra Gohar, 1948 is a common octocoral on the reefs of the Gulf of Eilat (northern Red Sea). Reproductive biology of C. hamra was studied for two years. Direct observations of spawning were conducted in situ and in aquaria. Cleavage of eggs and further embryo metamorphosis into mature planulae were examined by scanning electron microscopy and histological sections. Clavularia hamra is dioecious. Young oocytes appear annually in September, gradually grow in size and attain maturity within 11 months. The main spawning event of the population is highly synchronized, occurring on a single night each year between the last quarter and the new moon in mid summer. The released orange eggs are held together by mucus and remain attached amongst the polyps on the outside of the female colonies. Twelve hours after spawning, the young embryos have blastomeres of equal size with numerous microvilli on their external surface. Due to unequal cleavage, bizarre embryos are also formed. By 48 h a blastopore is visible, indicating that a gastrula is developing. Eight days after spawning mature planulae are observed. The external mode of embryo development on the surface of the parent colony reduces dispersal of the planulae. However, this reproductive feature enhances formation of locally dense populations of C. hamra, with distinct habitat preferences.     

Ecological Aspects of the Downstream Migration of Introduced European Eels in the Uono River, Japan

We examined the species composition, timing of downstream migration, and biological characteristics of eels using catches at three commercial weirs from 1996 to 1998 in the Uono River, Niigata Prefecture, Japan, which is located farther north in the Japan Sea than where most Japanese eels, Anguilla japonica, recruit. Analyses of a sub-sample of the 292 eels caught in the weirs found that 93.6% were introduced European eels, Anguilla anguilla, that were sexually maturing silver phase eels. Their average age based on otolith annuli was 10.2 years, indicating a relatively high average growth rate of 6.3 cm year^–1. Catch records in 1996 and 1997 indicated that downstream migration occurred sporadically from the middle of August to the end of November and that catches generally coincided with abrupt increases in water discharge and drops in water temperature. The highest catches in both years occurred between the last quarter and new moon. These findings were similar to studies on this species in Europe and indicate that A. anguilla can grow rapidly, begin maturation, and start downstream migration far from its native range. This discovery of introduced eels initiating their spawning migration at the same time as A. japonica raises concerns about the potential impact of interbreeding between species and the possible effects on the fishery resources of A. japonica.     

Mass spawning of Caesio teres (Pisces: Caesionidae) at Enewetak Atoll,Marshall Islands

Synopsis Mass spawning of Caesio teres occurred between March and August, 1983 on a reef emerging from deep water just inside the East Channel of Enewetak Atoll, Marshall Islands. Aggregations and spawning were observed from one day before until three days after the full moon. Spawning aggregations were not observed during the new or quarter moons. Spawning commenced after high tide, when the current began to flow out the pass from lagoon to ocean. The spawning aggregation of close to 1000 individuals migrated to the spawning site. Spawning occurred when the aggregate ascended to near the water's surface. Subgroups dashed horizontally within the aggregate, releasing a highly visible gamete cloud. Predation on spawning adults was not observed. Predation on spawned eggs was noted. The eggs of C. teres are described. Mid-Pacific Research Laboratory, Enewetak Atoll, Republic of the Marshall Islands Present address: Motupore Island Research Station, P.O. Box 320, University of Papua New Guinea, Papua New Guinea     

Lunar and daily spawning rhythms of Senegal sole Solea senegalensis

A periodicity of 29 days was observed in spawning rhythms in Senegal sole Solea senegalensis , with an acrophase around the last quarter and the new moon. In both spring and autumn, a very marked nocturnal spawning rhythm was registered, with spawning beginning after dusk and the acrophase occurring around 2300 hours. When the photoperiod was artificially extended (from 10L:14D to 14L:10D), S. senegalensis synchronized to the new photoperiod: spawning took place after the new 'dusk', the beginning gradually shifting from 2100 to 2300 hours and the acrophase from 2325 to 0032 hours. Under continuous light conditions, fish sustained rhythmicity for 2 days, with an acrophase at 2249 hours, which suggested the existence of an endogenous pacemaker controlling the daily spawning rhythm. These findings provided new insights for better understanding the reproductive physiology of this species and for optimizing the timing protocols of egg collection and larvae production in S. senegalensis aquaculture.     

Lunar synchronization of spawning in sea bass, Lates calcarifer (Bloch): effect of luteinizing hormone-releasing hormone analogue (LHRHa) treatment

Based on egg collection records, spontaneous spawning activity of sea bass, Lates calcarifer (Bloch), reared in floating net cages followed a semilunar cycle. The peak of multiple spawnings coincided with declining spring tides of quarter moon periods. Maximum diameter of intra-ovarian, ripe oocytes (0.51–0.55 mm) occurred in synchrony with the quarter moon periods. Smaller oocytes (0.44–0.47 mm) were sampled during the new and full moon periods. Two structural analogues of luteinizing hormone-releasing hormone (LHRHa) (des-Gly¹⁰, d -Ala⁶-LHRH ethylamide and d -Ala⁶, Pro⁹-Nethylamide-LHRH), in pelleted or dissolved form, induced mature female sea bass with a mean egg diameter of at least 0.40 mm to spawn at any day during the lunar cycle. The onset of spontaneous and LHRHa-induced spawnings occurred during low tides in the evening until dawn (from 19.00 to 05.00 hours). These results demonstrate that LHRHa can effectively induce mature sea bass to spawn independent of the highly predictable semilunar spawning rhythm. In addition, the occurrence of both spontaneous and hormone-induced spawnings at a precise period of the day suggest a tidal and diurnal cue entraining spawning of mature female sea bass.