Induction of Spawning in the Sea Cucumber Holothuria scabra (Echinodermata: Holothuroidea)

With the advent of sea cucumber aquaculture in the South Pacific region, a reliable method is needed to induce large numbers of animals to spawn in captivity. Broodstock of the sea cucumber Holothuria scabra , collected from Stradbroke Island, Moreton Bay (27°90'N, 153°24'E) Australia, during the reproductive season from October to January, were used in spawning trials. During the 1997–1998 summer between one to five weeks of captivity, 100% of animals were induced to spawn in four trials at dusk on or close to a new or full moon, using nine males and nine females contained in a Reln tank and 30 cm of filtered sea water, using a 3–5 C temperature shock. H. scabra was induced to spawn in small numbers during the 1996–1997 summer despite a marked degree of weight loss, and all animals spawned during 1997–1998 with minimal loss of weight. The difference in the number of spawned eggs between animals of similar size and mean numbers of spawned eggs in consecutive trials decreased the longer animals were held in captivity before spawning. The hatch rate of eggs was reduced significantly for broodstock held for more than one month. Hatch rate and numbers of spawned eggs are important indicators of egg viability of broodstock maintained in captivity for an extended period.     

Assessing the spawning season in common dentex (Dentex dentex) using microsatellites

A set of five variable microsatellite markers was used for the genetic characterization of two common dentex ( Dentex dentex ) broodstocks from an experimental hatchery and for the screening of the egg batches spawned during the complete spawn season in 2006. After parentage assignment, simulations were performed for the hatchery 1 broodstocks; the microsatellite set correctly assigned over 93% of descendants to parents when one parent was known and 80% when neither parent was known. Of the 261 eggs that the DNA was correctly amplified from, 254 were successfully assigned to a parental couple. More than one female or male took part (at the same point in time) in the spawning season. However, we observed 'dominant' individuals that produced high proportions of the descendants (unequal reproductive success) in all the sampling periods, although the contributions of these dominant individuals could change over time. This phenomenon reduces the effective breeding numbers, and could lead to inbreeding if this factor is not taken into account when the next parental generation is obtained. This factor should also be considered in aquaculture selection programmes because the dominant breeders may not be the most interesting individuals for commercial or productive schemes.     

Influence of diet on growth,reproduction and lipid and fatty acid composition in the sea cucumber Cucumaria frondosa

The suspension‐feeding sea cucumber Cucumaria frondosa is widely distributed in cold waters and is commercially exploited in the North Atlantic. While the species is considered to have potential for aquaculture, its feeding and reproductive biology differs markedly from that of currently cultivated sea cucumbers. Here, for the first time, the influence of food sources on the condition of C. frondosa was experimentally tested. Individuals were fed with either diatoms or fish eggs for 3 months. Specific growth rate (SGR), organ indices, fecundity, gonad maturity and profiles of lipids and fatty acids (FA) in tissues were compared among treatments and with sea cucumbers collected from the field. Individuals fed with fish eggs showed higher SGR and organ indices than all other treatments. The highest proportion of large oocytes was also found in gonad tubules of females from the fish egg treatment, although individuals fed with diatoms were the only ones in which spontaneous spawning occurred. Moreover, gonad and muscle tissues of sea cucumbers from the fish egg treatment presented the highest levels of lipids and essential FA. In contrast, non‐fed sea cucumbers showed negative SGR, relatively low female fecundity and low concentrations of lipids and FA in tissues. While the fish egg diet presented several obvious benefits, phytoplankton remains an important source of carotenoids, which are vital for vitellogenesis in echinoderms. This indicates that mixed diets rich in lipids, essential FA and carotenoids can be further investigated to optimize growth and reproductive output of this species in captivity.     

Skipped spawning in female iteroparous fishes

It is often assumed that iteroparous fishes spawn annually once reaching sexual maturity, but this is not always the case. This paper reviews available information on skipped spawning in female teleost fishes. All instances of non‐annual spawning are described as one of three types (retaining, reabsorbing, resting), depending on where in the normal spawning cycle development has been interrupted. Retaining ripe eggs is caused by conditions experienced during the spawning season (fish density, mate availability, pollution), whereas failure to start vitellogenesis (resting) or the breakdown of all oocytes that enter into vitellogenesis (reabsorbing) is caused by factors experienced prior to the spawning season (primarily temperature and poor nutrition). It is speculated that the relative shortage of data on non‐annual spawning may be because of difficulties in identifying non‐reproductive individuals. In an attempt to rectify this situation, the criteria needed to identify females undergoing the three forms of spawning omission are presented in terms of external appearance of gonads, gonad indices, and histological analysis. The energy saved by not spawning in a poor year may lead to increased survival and the probability of spawning in subsequent years. As the cumulative number of progeny gained by surviving to spawn in multiple subsequent years outweighs the number of progeny lost by not spawning in a given single year, occasional omission of spawning may constitute an adaptive trait in long‐lived iteroparous fishes.     

Reproductive characteristics of female longnose dace in the Coweeta Creek drainage, North Carolina, USA

Abstract – We examined the reproductive characteristics of 38 female longnose dace ( Rhinichthys cataractae ) from one of the southernmost populations of this species during two sampling periods in 1999 (ES=March 1999, LS=June 1999). Our data indicated that ES fish had not spawned, whereas LS fish had begun spawning. The smallest mature female captured was 56 mm SL (age 1+). Mean potential fecundity differed significantly between ES (mean±1 SD=1832±572 oocytes) and LS (mean±1 SD=775±415 oocytes) specimens. Potential fecundity was positively correlated with both standard length and somatic mass for both ES and LS specimens. Oocyte diameter frequency histograms indicated that ES specimens possessed two modes of oocytes, whereas LS fish contained two or three modes. Female longnose dace appeared to spawn more than once during a reproductive season. Oocyte number varied substantially both among individuals within periods and between periods. The number of Mode II oocytes in ES fish was positively correlated with both length and somatic mass. Female longnose dace appeared potentially capable of spawning 6+ clutches per year. GSI values for longnose dace ranged from a high of 21.4% (LS specimen) to 2.4% (ES specimen). Regression analysis demonstrated that there was no evidence of differential reproductive effort between longnose dace of different size in this population.     

Energy allocation patterns in a multiple spawning sunfish: evidence for an income‐based reproductive strategy

Timing of reproduction is an important life‐history trait that varies among species as a function of energy allocation strategy, particularly as individuals are influenced by seasonal variations prior to and during the reproductive season. This study investigated size‐ and sex‐based seasonal patterns of energy allocation in bluegill, Lepomis macrochirus (Rafinesque), a species that spawns repeatedly throughout the summer, by quantifying gonad, liver and mesenteric fat masses. Results indicate that bluegill delay production of gonad tissue until the onset of the spawning season and use an ‘income spawning’ approach. Comparisons of energetic trends with crappies, Pomoxis annularis (Rafinesque) and P. nigromaculatus (Lesueur), a confamilial species of relatively similar size and morphology that spawns in the spring, highlight the flexibility of energy allocation patterns even among relatively similar fishes and shed light on bluegill life‐history strategies.     

日本鳗鲡人工催产后亲鱼恢复培养与再催产效果

日本鳗鲡(Anguillajaponica)产后亲鱼的恢复培养全过程包括:产后亲鱼的海水淡化、诱导开口以及亲鱼培育。对2种不同淡化方式的结果比较发现,日本鳗鲡亲鱼的海水淡化方式以缓慢连续的方式较好,即每天换水1次,每次淡化量为总盐度的3%～4%,总淡化时间为1个月。淡化后的亲鱼存活率分别为:自然产卵的产后亲鱼达到100%,人工授精的产后亲鱼为86.3%,而难产的产后亲鱼则为81.5%。在各种开口驯养方式中,以水蚯蚓为开口饵料的驯养效果较好。诱导亲鱼开始摄食所需时间最短,为18d;摄食量也最大,达到平均体重的2.5%。从水蚯蚓逐步转为全人工饵料后,进行日常亲鱼培育。经18个月的恢复培养后,使产后亲鱼的平均体重雌鳗330g、雄鳗150g分别恢复到765g和470g。但2次繁殖的各项指标中,催熟率、成熟系数和性腺发育情况远远低于野生鳗,而催产率和幼苗存活率则略高于野生鳗,其原因尚有待进一步研究。     

Induced out-of-season and seasonal tank spawning and stripping of pike perch (Sander lucioperca L.)

Nine trials were carried out on the induced propagation of pike perch in out‐of‐season as well as in the natural reproduction period. From January till May, periodically, 16–20 pairs were transported to the hatchery, and acclimated to 15–16°C. The following hormonal treatments were used to induce reproduction: carp pituitary homogenate (CP) and human chorionic gonadotropin (hCG) alone or in combination; gonadotrop‐releasing hormone ‘Ovurelin’ (D‐Phe⁶‐LH‐RH) alone or with metaclopramid (MTC); and ‘Ovopel’ [containing des‐Gly¹⁰‐(D‐Ala⁶)‐LH‐RH‐ethylamide and MTC]. The effects of daylight regime, water temperature and the length of the pre‐spawning conditioning period on the reproduction performance were determined. From the 130 hormonally treated pairs, 122 either spawned in tanks or were stripped. There were no differences in the ovulation rate between out‐of‐season (93%) and seasonal (91%) propagation. The developmental stage of the eggs correlated with the latency period, which significantly declined from January till April. The latency period was the shortest in fish treated with hCG and, secondly, with CP. The germinal vesicle migration did not proceed without hormonal treatment, although in some trials breeders were kept at the spawning temperature for 1–2 weeks. The results demonstrate that the pike perch can be successfully induced to spawn about 3 months earlier than its natural spawning season, which allows a significantly prolonged yearly supply of fry.     

Notes on hatchery spawning methods for bigmouth sleeper Gobiomorus dormitor

The bigmouth sleeper Gobiomorus dormitor, a popular sport fish within its native range, offers a management alternative to exotic species currently managed for recreational fishing. Hatchery production and stocking are needed to create reservoir sport fisheries because this species usually requires access to marine environments for recruitment. Bigmouth sleepers have not been spawned previously in a hatchery, and hence we used natural, artificial and semi‐natural spawning techniques. No egg deposition or propagation resulted from natural pond spawning. Artificial spawning techniques using Ovaprim^® and Chorulon^® injections followed by hand stripping were more successful. Semi‐natural (hormone injections plus volitional spawning) spawning trials using Ovaprim^® and Chorulon^® displayed the greatest potential, and three consecutive evening injections (1.0 mL kg^?1) of Chorulon^® appeared most conducive. High‐fecundity spawning was achieved by injecting bigmouth sleeper pairs and allowing volitional spawning in aquaria with spawning cavities. Initial success in 2007–2008 was isolated to wild‐caught fish, but captive broodstock were spawned using these techniques in 2009. Eggs hatched in <20 h at 23–24 °C. The resulting larvae, 1.0–1.5 mm in length, displayed large yolk sacs, unpigmented eyes and no apparent mouth. These hatchery propagation efforts suggest that hormone‐induced semi‐natural spawning has the greatest potential for bigmouth sleeper propagation.     

The reproductive cycle of the ‘blunt’ sea urchin

The reproductive cycle of the blunt sea urchin, Sphaerechinus granularis (Lamarck), was studied in the Bay of Brest, West Brittany, from monthly samples by examining seasonal changes in gonadal index, in the stages of gonad development and in oocyte diameters. This echinoid exhibited an annual cycle of gonadal growth, with a short breeding season occurring in May and June, and a decrease in gonadal index during the winter attributed to the use of nutrient resources. Histological examinations defined long mature stages during autumn, winter and early spring, where the vitellogenic oocytes accumulated in the lumen of the gonad. Changes in oocyte diameters showed a short pre-spawning period in April and May. The brief breeding season was followed by rapid post-spawning recovery and gonad growing stages during the summer, where the gonads mainly grew through the development of nutritive tissue. The features of this reproductive cycle show that the species can be commercially exploited and these results are used to make recommendations in terms of the management of S. granularis fisheries in Brittany. The influence of temperature on the initiation of spawning was noted again. This exogenous factor could be monitored to improve gonad production and availability of mature gametes in mariculture projects. © Rapid Science Ltd. 1998     

Reproductive cycle,sexual maturity and diel-reproductive periodicity of white croaker,Pennahia argentata (Sciaenidae), in Ariake Sound,Japan

The white croaker, Pennahia argentata (Houttuyn), is abundant in demersal fish assemblages in Ariake Sound and is a commercially important species. The reproductive biology of white croaker was studied by measurement of gonadosomatic indices (GSI) and histological examination of ovaries. Ovaries were classified into one of five maturity stages based on histological data: (1) immature/resting stage; (2) developing stage; (3) maturing stage; (4) ripe/spawning stage; (5) spent stage. The spawning season lasts from April to September but most activity is observed from May to August. Age at sexual maturity was assumed to be 1 year. Postovulatory follicles coexisted with yolk stage oocytes in histological sections of ovaries indicating that white croaker is a multiple spawner, spawning more than once in a single spawning season. Judging from the diel changes in the proportion of females with ovaries containing postovulatory follicles and oocytes at maturation stage, most females spawned in the evening between 19:00 and 21:30 h.     

半滑舌鳎卵巢发育的组织学和形态数量特征研究

采用组织学方法系统研究了人工养殖条件下半滑舌鳎亲鱼卵巢的组织发育周年变化特征.结果表明,卵母细胞发育可分为6个时相,卵巢发育分为6期.卵巢不同发育时期都由不同类型的卵母细胞组成,半滑舌鳎为非同步分批多次产卵类型.周年发育过程中,6月龄前的鱼卵巢发育处于第Ⅰ期;9～12月龄卵巢可发育至第Ⅱ期;12月龄半滑舌鳎性腺可发育达到Ⅲ期,并一直保持至24月龄.3龄雌鱼达到性成熟,卵巢可发育至第Ⅳ期;随着水温和光周期的调控,卵巢发育进入成熟期(Ⅴ期),发生水合现象是卵母细胞成熟并准备排卵的信号;产卵结束后卵巢退化至第Ⅵ期,排出的卵母细胞退化吸收,以Ⅲ期卵巢越冬后,卵巢退化至Ⅱ期并持续至下一个繁殖周期.人工养殖条件下,卵巢内存在卵母细胞闭锁现象.性腺周年发育过程中,性腺指数(GSI)在性腺达到成熟期时达到峰值,产卵结束后性腺快速退化,GSI值各月份差异显著(P<0.05),亲鱼性腺重量在卵巢发育成熟过程中一直处于生长状态.亲鱼肝脏指数(HSI)在产卵前7～8月份(性腺达到成熟期前30 d左右)达到最大,表明7～8月份是性腺进行卵子发育、卵黄能量储备的重要时期,亲鱼在产卵前通过积极摄食储备体内能量,肝脏在卵母细胞卵黄积累方面具有重要的生理作用.肥满度(CF)值在繁殖盛期10～11月份达到最大,表现出与GSI类似的变化趋势.     

High variability in spawning migration of sea trout,Salmo trutta,in two northern Swedish rivers

Abstract Telemetry was used to examine spawning migration of sea trout, Salmo trutta L. (n = 126), in two rivers in northern Sweden. The spawning areas defined by radio‐tagged fish differed between the river systems. In the River Vindelälven, sea trout spawned in the main stem and 80% of tagged individuals returned to areas where hatchery‐reared juveniles had been previously stocked. In the River Piteälven, 74% of tagged sea trout ascended tributaries for spawning. Tagged fish were categorised into three groups of migratory pattern. cart (classification and regression tree) analysis indicated that distance from tagging location to spawning site (S_dist) explained the migratory patterns. Large S_dist separated fish with stepwise upstream migration from those with up‐ and downstream migrations and one‐directional direct migration. Fish tagged early in the season migrated the longest distance to spawning areas. Stocking locations and sex explained the large search behaviour up‐ and downstream in the rivers. The findings are important for the sustainable management of sea trout in the Gulf of Bothnia.     

Spawning by Captive Serranid Fishes: A Review

The current available information on spawning by serranid fishes in captivity is reviewed. Much work has been done on members of the family Serranidae because of their value as food or ornamental fish. At least 31 species have been induced to ovulate with hormones, and at least 23 species have spawned voluntarily (without chemical treatment) in captivity. Typically, a serranid female with fully-yolked oocytes will ovulate within 24–72h (usually 36–50h) after the first of 1–3 injections of 500–1,000 IU human chorionic gonadotropin/kg body weight. Similar results have been obtained for several species given 1–3 injections of 10–50μg luteinizing hormone-releasing hormone analog/kg body weight. Voluntary spawning has occurred mostly with well-fed uncrowded fish during the natural spawning season under conditions of ambient temperature and partial or total natural light. The necessary temperature range for spawning varies among species, and daylength seems to be a less important stimulus than temperature for serranids.     

Multiple spawning and related variations in female reproductive parameters of amphidromous type ayu

Adult ayu Plecoglossus altivelis were sampled from the Nezugaseki River, Yamagata Prefecture to investigate the reproductive parameters and analyze their variations related to multiple spawning. Ovarian histology (mainly based on the occurrence of postovulatory follicles) indicated that female ayu can be divided into four groups, which are considered to correspond with unspawned, once spawned, twice spawned, and three (or more) times spawned individuals. Comprehensive analysis of the ovarian state with field surveys revealed that most of the female ayu achieve second spawning and that third spawning is very common in this river. Mean relative batch fecundity (RBF) for the second, third, and fourth spawning indicated 69, 42, and 22%, respectively, of the value for the first spawning, showing a decline with the number of spawning batches. Mean gonadosomatic index (GSI) values of non-ovulating fish showed a similar decline during the main spawning period (October). Condition factor (without gonads) during autumn also decreased with the number of batches spawned, suggesting that multiple spawning is achieved partly by transfer of body mass nutrients to the ovary. Size dependency in reproductive parameters such as occurrence of the multiple spawning, RBF values, and GSI values of the unspawned fish, was not evident except for GSI values in early September (generally during the early phases of ovarian development), when larger fish had larger GSI.     

Volitional Spawning of Black Sea Bass Centropristis striata Induced with Pelleted Luteinizing Hormone Releasing Hormone-Analogue

The black sea bass is a high‐value marine serranid and is a prime candidate for intensive cultivation. Reliable methods for controlled spawning are needed to accelerate the development of hatchery technologies that result in mass production of healthy juveniles. During 1998–2001, spawning studies were conducted at The University of North Carolina at Wilmington (UNCW) and at the South Carolina Department of Natural Resources (SCDNR), Charleston, using pelleted luteinizing hormone releasing hormone analogue (LHRH‐a). From April through July 2001, 28 vitellogenic‐stage females, with mean oocyte diameters (MOD) ranging from 277–448 μm, were implanted with a 95% cholesterol‐5% cellulose pellet containing LHRH‐a (‐50 μg/kg body wt) at UNCW. In 10 individual spawning trials, females with MOD of 305–448 μm and maximum oocyte diameter × 475 μm spawned volitionally beginning 2–3 d post‐implantation (PI) and continued spawning over an average of 1.9 d (range = 1–4 d). Individual females released a mean total of 149,000 eggs (117,000 eggs/kg) with a mean buoyancy rate of 40.5% (floaters). Fertilization and hatching rates were 98% and 27.2% of floaters, respectively, yielding 14,600 yolksac larvae/female (12,600 yolksac larvae/kg body wt), and overall egg viability averaged 8.9%. In eight group spawning trials (2–3 females/group), average performance of females, including fecundity (103,800 eggs/female; 105,500 eggs/kg body wt), buoyancy rate (42.5%), fertilization and hatching rates (97.7% and 24.3% of floaters), numbers of yolksac larvae produced (10,900 yolksac larvae/female; 10,100 yolksac larvae/kg body wt), and overall egg viability (10.6%) was comparable to what was seen in individual spawning trials. From 1998–2000, a total of 58 vitellogenic stage (70% of oocytes 500 pm) females were implanted with pelleted LHRH‐a (‐50 μg/kg body wt) in nine group spawning trials (2–19 females/group) at SCDNR. Volitional spawning typically began 18–42 h PI and recurred every 1–3 d for an average duration of 9 d. Female groups released a mean of 560,000 eggs (84,000/female; 132,000/kg body wt) over the spawning period, with mean buoyancy rate of 25.7% floaters. Fertilization and hatching rates were 17.7% and 11.6 % of floaters, respectively, yielding 4,300 yolksac larvae/female (4,600 yolksac larvae/kg body wt). Overall egg viability was 2.9%. Captive wild‐caught black sea bass were induced to undergo repetitive volitional spawning by implantation of pelleted‐LHRH‐a, consistent with a multiple clutch group synchronous pattern of ovarian development. Group spawning appears to be a practical way to compensate for variable fecundity and egg viability of individual females. Research is needed to identify optimum hormone treatments and eligibility requirements.     

Spawning frequency of the Tsushima Current subpopulation of chub mackerel <Emphasis Type="Italic">Scomber japonicus</Emphasis> off Kyushu,Japan

Female Japanese chub mackerel Scomber japonicus of the Tsushima Current subpopulation were collected during the spawning season from March to May 2001. A total of 137 adult females were caught between midnight and daybreak. A considerable number of fish displayed new postovulatory follicles (POF), whereas there was no evidence of germinal vesicle breakdown or hydrated oocytes in any of the fish collected. This suggests a daily spawning synchronicity toward midnight. To estimate the spawning frequency (S), the female reproductive state was classified into four criteria based on the degenerative stage of the POFs and the developmental stage of the oocytes. To stage the POFs according to age and determine the stage duration, ovaries from S. japonicus were induced to spawn in the laboratory and were sampled 0–72 h after ovulation at appropriate intervals. The average S, which is evaluated from four different indices, was 16.9%, corresponding to the average female chub mackerel spawned every 5.9 days (8.5 times) during the 50 days.     

Spawning induced by cubifrin in the Japanese common sea cucumber <Emphasis Type="Italic">Apostichopus japonicus</Emphasis>

The neuropeptide cubifrin-I and its derivative cubifrin-L have recently been shown to be potent substances that induce in vitro oocyte maturation and spawning in the Japanese common sea cucumber Apostichopus japonicus. We have examined the reproductive behavior of A. japonicus in vivo following the injection of cubifrin-L into the body cavity with the aim of determining the practical value of using this peptide to induce spawning in the hatchery setting. The responsiveness of ovarian fragments with oocytes >155 μm in diameter to cubifrin-L in vitro was well correlated with the spawning success induced in vivo by a cubifrin-L injection. Mature sea cucumbers injected with cubifrin-L displayed sequential reproductive behaviors, which comprised climbing up the side wall of the tank toward the water surface, waving of the head, and shedding of gametes. Gamete shedding started about 60 and 80 min after the injection of cubifrin-L in males and females, respectively, and was completed almost simultaneously in the two sexes about 2 h post-injection. Repeated injections of cubifrin-L at intervals of about 10 days successfully induced multiple spawnings in males and females. These results demonstrate that cubifrin-L can be used as an effective inducer of spawning in Japanese sea cucumber cultivation.     

Sources of Vibrio bacteria in mollusc hatcheries and control methods: a case study

Results of a 1‐year intensive monitoring of Vibrio bacteria, as thiosulphate citrate billar salt sucrose (TCBS) counts, in a hatchery for molluscs, are presented. Surface seawater, well seawater, tap water from a freshwater well, microalgae system, including pasteurized well seawater, f/2 medium, starter cultures of eight micro algal species, mass‐produced microalgae and compressed air were studied as possible sources of Vibrio. Additionally, recently collected broodstock of the catarina scallop Argopecten ventricosus (Sowerby II 1842) was also subjected for investigation for their possible role in discharging Vibrio during spawning. Efficiency of a cartridge–ultraviolet (UV)‐filtration system and of a steam gun employed for sterilizing tanks, hoses and utensils was also determined. Results indicated that Vibrio were present in surface seawater throughout the year. In well seawater these bacteria were only found during the first 5 months soon after construction of the well and before commencement of continuous operations, but not after this period. Vibrio was never detected in pasteurized well seawater, f/2 medium, starter cultures of microalgae and compressed air. However, mass‐produced microalgae contained Vibrio, possibly as a result of the use of contaminated tap water for washing and rinsing the fibreglass culture tanks. Scallop broodstock was found to be an important source of Vibrio in the hatchery. Biopsy on female gonads of live organisms demonstrated higher numbers of colony‐forming units than male gonads. At spawning, Vibrio was released into water, producing bacterial blooms in tanks after 24 h. The cartridge–UV‐filteration system was not sufficient to eliminate the bacteria from seawater, but the steam gun proved to be a good tool to eliminate Vibrio biofilms on tank walls or tools used in the hatchery. Some recommendations are given, which could be useful for other mollusc hatcheries.     

Semilunar spawning periodicity in brackish damsel Pomacentrus taeniometopon

ABSTRACT:   Lunar-related spawning periodicity of the brackish damsel Pomacentrus taeniometopon was investigated by changes in gonadosomatic index (GSI) and ovarian histology. During the spawning season, GSI increased toward the week of the first and last quarter moon. Concomitant with increases in GSI, oocytes laden with yolk developed from the new/full moon to the first/last quarter moon. Postovulatory follicles appeared in the ovary around and after the first/last quarter moon. These results suggest that P. taeniometopon is a semilunar spawner and repeats spawnings twice a month with lunar periodicity during the spawning season. When the fish were reared under laboratory conditions without periodicity of tide, the spawning of P. taeniometopon occurred sporadically. It is likely that the fish uses tidal stimuli in the natural habitat to entrain reproductive activities.