Annual and lunar-synchronized ovarian activity in two rabbitfish species in the Chuuk lagoon, Micronesia

ABSTRACT:   This study examined the annual and the lunar cycles of ovarian activity in the forktail rabbitfish Siganus argenteus (Quoy & Gaimard, 1825) and the spiny rabbitfish Siganus spinus (Linnaeus, 1758), which were collected from the Chuuk lagoon, Federated States of Micronesia. Gonadosomatic index (GSI) increased in May and June for S. argenteus . For S. spinus , GSI increased in March, and from July to September. During these periods, the ovaries of these species contained oocytes at the tertiary yolk stage or the maturation stage, suggesting that these months are the reproductive season of the two species. During the reproductive season, weekly collection of the fish according to the lunar phase revealed that high GSI occurred around the last quarter moon for S. argenteus and the new moon for S. spinus . In the ovaries, oocytes developed synchronously, and postovulatory follicles, an indicator of spawning, were observed after the respective moon phase, suggesting that these species are restricted lunar-synchronized spawners. Comparisons of the reproductive activity of the two rabbitfishes in the Chuuk lagoon with that in Okinawa waters revealed that there is a geographic difference in the reproductive activity between habitats. However, the lunar phase for exertion of synchronous gonadal maturation and spawning is common in both regions.     

Histological observations of seasonal reproductive and lunar-related spawning cycles in the female honeycomb grouper Epinephelus merra in Okinawan waters

Seasonal reproductive and lunar-related spawning cycles of the female honeycomb grouper Epinephelus merra inhabiting Okinawan waters were examined by histological observation of ovaries. Gonadosomatic index (GSI) increased beginning in May and peaked in June. Histological observations revealed that many oocytes laden with yolk were present in the ovaries from May to August. From September to October, ovaries were occupied by immature oocytes. These results suggest that the reproductive season of E.   merra lasts for 4 months from May through August in Okinawan waters. When the fish were collected according to the lunar cycle, GSI increased with the approach of the full moon. Oocytes at various development stages were observed from the first quarter to the full moon. Fresh ovulatory follicles were present in the ovaries around the last quarter moon. These results suggest that E.   merra has a lunar spawning cycle and spawns between the full moon and the last quarter moon. Ovarian features of the fish collected around the last quarter moon were different among individuals; some fish had many oocytes at the tertiary yolk stage in the ovaries, while the ovaries of the others were occupied by the oocytes at the peri-nucleolus and the oil droplet stages. This observation suggests that a minor release of eggs occurs in this species before or after a major spawning lunar day. Oocytes at the migratory nucleus and the maturation stages were not observed in any ovarian samples. This may mean that maturation of oocytes is related to the spawning behavior of this species and makes rapid progress in the process of aggregation at the spawning sites.     

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.     

Oogenesis and lipids in gonad and liver of daubed shanny (Leptoclinus maculatus) females from Svalbard waters

Oocyte and liver histomorphology of the daubed shanny (Leptoclinus maculatus) from Isfjorden and Kongsfjorden in Svalbard were investigated during three Arctic seasons: summer (July), autumn (October) and winter (April). Three oocyte developmental phases were observed: primary growth phase, secondary growth phase and maturation phase. We observed four different developmental stages: (1) perinucleolus stage with cortical alveolus formation, (2) lipid droplets formation, (3) vitellogenesis stage and (4) maturation. Late maturation stage of oocytes in the ovaries was from the autumn season. Females accumulated lipids in liver (up to 35.2?% dw) and deposited large amounts of lipids into gonads (up to 52.2?% dw) during maturation. Lipid classes in female gonads changed seasonally, with relative increase in cholesterol during summer and depletion of storage lipids (triacylglycerols and wax esters/cholesterol esters) during the winter. Lipid composition in liver changed during oocyte development and spawning, as neutral lipids were transferred to developing oocytes during summer to autumn. During winter, storage lipids were depleted during starvation. Based on the increase in gonadosomatic index (GSI) with length and observed maturation stages, females seem to mature at a length of about 125-130?mm. The GSI and hepatosomatic index of large females sampled in autumn (September-October) were significantly higher than for females in late winter (April) and spring (May). These results indicate that spawning takes place during winter in Isfjorden and that energy reserves stored in the liver are utilized by females during gonadal development and reproduction.     

Aspects of the reproductive biology of the sharpsnout seabream Diplodus puntazzo (Cetti, 1777). I. Gametogenesis and gonadal cycle in captivity during the third year of life

A histological study was made of the reproductive cycle of captive sharpsnout seabream Diplodus puntazzo during the 3rd year of life. All specimens contained both ovarian and testicular tissue. Ovarian tissue prevailed in 64 out of 120 fish sampled throughout one year. The ovary underwent a long resting phase from October to August, during which time it contained oogonia, primary growth phase (PGP) and occasional yolk vesicle stage oocytes. Intense ovarian development took place in September leading to the formation of advanced vitellogenic oocytes. Final maturation and spawning were not achieved in any of the fish. The testicular area in the predominantly female gonads contained only spermatogonia and was found to be histologically normal in 76% of individuals, but severely regressed in the remaining fish. The testicular portion was found to be dominant in 56 out of 120 fish sampled throughout one year. These underwent a resting phase from November to July, a maturing/pre-spawning phase in August, and a spawning phase with spontaneous sperm release in September to October, as in the natural environment. The ovarian portion in the functional male gonads contained only oogonia and oocytes which did not develop beyond the perinucleolus stage at any point during the reproductive cycle. Apart from the pre-spawning/spawning phase, during which the gonadosomatic index (GSI) was comparable in the two groups, the GSI values were approximately ten-fold higher in those fish in which the ovary predominated than in those in which the testis predominated.     

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.     

Maturation and spawning of the small penaeid shrimp Metapenaeopsis dalei in Tosa Bay, Pacific coast of southern Japan

SUMMARY: Seasonal changes in the percentage of mature female Metapenaeopsis dalei were studied histologically, and the annual cycle of maturation and spawning of this species was discussed. Specimens were collected at night by a beam trawler in Tosa Bay (33°N, 133°E) during the period from April 1995 to March 1996. All individuals had a gonado somatic index [ GSI = 100 (gonado weight/body weight)] of higher than 8, and 66.7% of those individuals with a GSI of 6–8 had oocytes in the late phase of the prematuration stage after germinal vesicle shrinking and migrating to the margin of the oocyte or had oocytes in the maturation stage. Such individuals with developed oocytes appeared in April, June, July, August, October, November and March. Individuals with a GSI above 6 appeared throughout the year, except during September and February. Individuals with ovulated oocytes were sampled in March when the water temperature near the bottom depths was lowest (15.4°C) during the year, being similar to February (15.1°C). These facts indicate that maturation occurs all year-round and suggests that spawning in the Metapenaeopsis dalei population in Tosa Bay occurs all year-round. This is the first report of year-round maturation in penaeid shrimps in Japanese waters.     

Lunar cycles and reproductive activity in reef fishes with particular attention to rabbitfishes

Cues from the moon influence synchrony in growth, feeding, migration, behaviour and reproduction of many reef fishes. Compared with comprehensive studies on the annual and daily activities of fish, few physiological studies have paid attention to the importance of lunar cues in reproductive activities. We review mutual and interesting relationships between fish reproduction and environmental changes induced by the moon, with particular emphasis on the reproductive activity of the rabbitfishes (Siganidae). Rabbitfish species exhibit, in nature, a definitive reproductive season, which differs among the tropical areas. During the reproductive season, synchronous spawning of rabbitfish is associated with a particular lunar phase. The lunar phase used by the respective species is similar in different regions on the earth. Histological observations revealed that gonads develop synchronously towards a peak around the spawning lunar phase, after which the gonads return to spent condition. Concomitant with gonadal development, sex steroid hormones were produced under the influence of gonadotropin (GtH). Injections of human chronic gonadotropin (hCG) to the fish that are undergoing active spermatogenesis accelerated testicular maturation. These results suggest that hormonal response in maturing the gonads in rabbitfish is under the regulation of GtH, and that pituitary secretion of GtH according to the lunar cycle accounts for the lunar rhythm in gonadal development. We speculate that the cues from the moon can be recognized by the higher parts of the hypothalamus–pituitary–gonadal axis. Possible relationships between exogenous environmental factors and the lunar‐reproductive rhythm are also discussed.     

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.     

Reproductive cycle of yellow sea bream <Emphasis Type="Italic">Dentex tumifrons</Emphasis> in Wakasa Bay,the Sea of Japan off central Honshu

ABSTRACT:   To determine the spawning season and reproductive cycle of the yellow sea bream, Dentex tumifrons , in Wakasa Bay, in the Sea of Japan off central Honshu, seasonal change in the gonadosomatic index ( GSI ) was examined and histological observations of both ovaries and testes were conducted. The female GSI gradually increased from May, maintained a high level between August and October and then rapidly decreased. The histological observations of the ovary showed that vitellogenesis began from May and developed until September. Spent fish began to be observed in October and all the fish collected in December were spent. There was only one peak in the seasonal change in GSI of males and females in Wakasa Bay. Thus, yellow sea bream spawn only in autumn in Wakasa Bay. Differences in the reproductive cycle and number of spawning seasons were found between the two different latitudinal areas, Wakasa Bay and the East China Sea (low latitudinal area) where the spawning seasons were spring and autumn. An increase in water temperature is an important factor to initiate gonadal maturation (recrudescence) and is terminated by the short day-length in Wakasa Bay.     

Effect of temperature and photoperiod on the reproductive condition and performance of a tropical damselfish <Emphasis Type="Italic">Chrysiptera cyanea</Emphasis> during different phases of the reproductive season

Effects of temperature and photoperiod on the reproductive activity of a reef associated tropical damselfish Chrysiptera cyanea were evaluated under three phases with different environmental patterns, phase I (April–May; increasing water temperature and photoperiod), phase II (June–July; increasing water temperature and peak/decreasing photoperiod), and phase III (August–September; peak/decreasing water temperature and decreasing photoperiod). When the fish were reared at 20, 25, or 30°C under natural photoperiod, the reproductive conditions differed within and among the phases depending on experimental temperature and environmental patterns. From phases I through III, ovaries with vitellogenic oocytes were notable only at 25°C, whereas regressing and immature oocytes were noticed at 20 and 30°C. The fish underwent active spawning at 25°C, whereas no or few spawnings were observed at other temperatures. In phase III, there was a resultant prevention of decrease in the gonadosomatic index and disappearance of vitellogenic oocytes in the ovaries of fish under a long photoperiod (LD14:10) compared to those under a short photoperiod (LD10:14). These results indicate that a long photoperiod with a suitable range of water temperature is a principal determinant in continuity of reproductive activity and performance, and that a high temperature has a negative impact on their ovarian development.     

Solar and lunar influences on the spawning activity of Pacific bluefin tuna (Thunnus orientalis) in the south‐western North Pacific spawning ground

Pacific bluefin tuna (Thunnus orientalis) migrate to the south‐western North Pacific spawning grounds (area off Taiwan and the Ryukyu Islands) from mid‐April to early July. Reproductive traits of the species in this area have been studied for some time; however, temporal changes in spawning activity during this season are not well understood. In this study, the spawning fraction (proportion of females with post‐ovulatory follicles to total mature females) in relation to solar calendar date and lunar day was investigated using a generalized linear model. Sampling was conducted almost every day throughout the fishing season at Ishigaki Fishing Port (24°21′N, 124°09′E), southern Japan between 2012 and 2014, and a total of 212 ovaries were histologically observed. Spawning fraction continued to increase from the beginning to the end of the season. This indicates that the peak season of occurrence in the area and the peak of spawning activity did not co‐occur. Spawning fraction also changed with the lunar day and significantly increased around the new moon. Eggs and early larvae hatched around the new moon may have reduced the predation risk during night‐time. These findings improve the current knowledge of reproductive biology and resource evaluation of Pacific bluefin tuna and indicate that spawning activity is not constant, and has two or three peaks in each season.     

Annual reproductive cycle of the greasyback shrimp Metapenaeus ensis in Ise Bay,Japan

The greasyback shrimp Metapenaeus ensis is widely distributed along the coast of India and the West Pacific where it is an important fisheries species. We have examined seasonal changes in ovarian development, spermatogenesis, and mating of Me. ensis in histological studies and by external observations on specimens collected in Ise Bay, its northernmost habitat. Ovaries were found to be previtellogenic from February to May, with the first signs of development being the accumulation of yolk in oocytes in late May. Ovarian shadow ratios were high during the period late July to mid-September. The formation of cortical rods in the peripheries of oocytes and germinal vesicle breakdown were observed in ovaries from late June to September. Male shrimps had sperm in the testes during the period early June to early October, and female shrimps had spermatophores in spermatheca after early July. In late July, some post-spawn female shrimps had exogenous vitellogenic oocytes in their ovaries, indicating that ovarian development had been repeated in preparation for the next spawning. Ovarian shadow ratios, which were positively correlated with gonadosomatic indices and ovarian development, seem to be a useful marker to determine ovarian development. Our results indicate that mating in Me. ensis started in early July and that the spawning season ranged from July to September with more than two cycles of spawning in Ise Bay.

     

Maturation and spawning of <Emphasis Type="Italic">Spratelloides gracilis</Emphasis> Clupeidae in temperate waters off Cape Shionomisaki,central Japan

ABSTRACT:   The reproductive ecology of Spratelloides gracilis was investigated in the temperate waters off Cape Shionomisaki, central Japan. Cape Shionomisaki is located at the northern margin of the distribution range of this species. Females of S. gracilis with gonadosomatic index (GSI) ≥ 4.0 were defined as mature based on the relationship between GSI and the histological maturity phases of their ovaries. More than 50% of females greater than 60 mm standard length (SL) were mature. Hatch dates of larvae and juveniles collected in the study area were determined by otolith daily ring counts and found to extend from April to November. The size at maturity of females (60 mm SL) and the spawning season of S. gracilis in the temperate waters off Cape Shionomisaki (April–November) was larger and shorter, respectively, than those in tropical waters in the western Pacific. The reproductive traits observed for S. gracilis off Cape Shionomisaki appear to be adaptive to northern temperate waters with seasonal changes in environmental conditions.     

Comparing histology and gonadosomatic index for determining spawning condition of small-bodied riverine fishes

Abstract –  We compared gonadosomatic index (GSI) and histological analysis of ovaries for identifying reproductive periods of fishes to determine the validity of using GSI in future studies. Four small-bodied riverine species were examined in our comparison of the two methods. Mean GSI was significantly different between all histological stages for suckermouth minnow and red shiner. Mean GSI was significantly different between most stages for slenderhead darter; whereas stages 3 and 6 were not significantly different, the time period when these stages are present would allow fisheries biologists to distinguish between the two stages. Mean GSI was not significantly different for many histological stages in stonecat. Difficulties in distinguishing between histological stages and GSI associated with stonecat illustrate potential problems obtaining appropriate sample sizes from species that move to alternative habitats to spawn. We suggest that GSI would be a useful tool in identifying mature ovaries in many small-bodied, multiple-spawning fishes. This information could be combined with data from histology during mature periods to pinpoint specific spawning events.     

Analysis of germ cell proliferation, apoptosis, and androgenesis in the Lake Van fish (Chalcalburnus tarichi) during testicular development

In the present study, the testis histology, gonadosomatic index (GSI), germ cell proliferation and apoptosis, and the plasma 11-ketotestosterone (11-KT) and testosterone (T) levels of male Chalcalburnus tarichi were analyzed. According to the histological examinations of the specimens that were caught between February 2009 and January 2010, three testicular stages were determined. Those stages were as follows: (1) recrudescence or prespawning (July–April), (2) spawning (May–June), and (3) postspawning (July). It was observed that the GSI increased gradually, starting from the recrudescence stage, and it reached peak values at the spawning stage, while the lowest values were in the postspawning. Germ cell proliferation in the testis was detected using a proliferating cell nuclear antigen (PCNA), and germ cell apoptosis was detected by transferase dUTP nick end labeling staining. The germ cell PCNA and apoptosis index values were calculated. It was indicated that germ cell proliferation was observed in all of the testicular stages. The highest germ cell PCNA index (PI) levels were detected in July, August, and September, which then dropped in October and stabilized between February and April. The lowest PI values were detected in the spawning stage (May–June). Germ cell apoptosis was observed in all of the months, and the highest apoptotic index values were detected in August, September, October, May, and June. Plasma 11-KT and T levels were at their highest levels in May and June, and it was detected as stabile in the other months. There was a correlation between GSI, PI, and plasma androgen levels. In conclusion, the present data illustrate testicular development stages for C. tarichi and show changes in the level of GSI and sex steroid biosynthesis through spermatogenesis.     

细鳞鲴卵巢发育的组织学观察

采用组织学方法对细鳞鲴卵巢周年变化和卵母细胞发育进行了观察研究。结果表明,细鳞鲴卵巢发育分为6个时期,卵母细胞发育分5个时相,从第Ⅲ时相卵母细胞开始表现出种的特异性。3月卵巢处于产前发育阶段,4-7月为繁殖期,5-6月为繁殖盛期,8月卵巢基本修整完毕,9-10月为Ⅱ′期发育,11月至翌年2月以Ⅲ期卵巢越冬。细鳞鲴的产卵方式为短期分批同步产卵类型,在一个生殖周期内一般产卵2~3次。     

Maturation and reproductive cycle of female armorhead <Emphasis Type="Italic">Pseudopentaceros wheeleri</Emphasis> from the southern Emperor—northern Hawaiian Ridge Seamounts

ABSTRACT:   The stage of ovarian development and annual reproductive cycle of female armorhead Pseudopentaceros wheeleri collected from seamounts of the southern Emperor–northern Hawaiian Ridge in 1993 and 1995–1996 was investigated through use of the gonadal somatic index ( GSI ) and ovarian histology. The stages of oocyte development were classified into eight developmental stages (perinucleolus, cortical alveolus, oil droplet, early yolk globule, late yolk globule, migratory nucleolus, prematuration, and maturation) based on histological characteristics. Oocytes of different size and developmental stage were present within ovaries during the spawning season. Oocyte development appears to be asynchronous and armorhead apparently spawn several times during the spawning season. The stage of the most developed oocyte was used to classify the stage of ovarian maturation. The GSI increased gradually with ovarian development. Oocytes in the perinucleolus, cortical alveolus, and oil droplet stages were present in ovaries throughout the year. Early and late yolk globule stages appeared during August–September indicating that yolk formation begins during late summer. The migratory nucleolus through maturation stages were detected during November–January. Post ovulatory follicles were present during November–March, and GSI values rapidly decreased in February. Results indicate that spawning occurs during November–February and peaks during December–January.     

Reproductive biology of <Emphasis Type="Italic">Sillago aeolus</Emphasis> in Okinawa Island,Japan

ABSTRACT:   A total of 414 fish (female, 59.3–275.0 mm and male, 61.0–220.0 mm standard length) were collected from December 2000 to March 2002 around Okinawa Island, Japan, for the determination of sex, spawning season, maturity and fecundity. Monthly changes in the gonadosomatic index (GSI) exhibited similar trends for both sexes and the mean GSI maintained a high level between February and May. Furthermore, the percentage frequency of hydrated oocytes and the spermatozoic activity suggested that main spawning occurred between February and May. Some hydrated oocytes were found throughout the year, with a GSI value greater than 1.0, suggesting that sporadic spawning occurred. Length at first maturity was determined for females and males as 120 and 113 mm standard length, respectively. Almost 50% and 100% males were matured at the end of their 0 and 1 year of age group, respectively. In contrast, no females were found to be mature at 0+ age group, and almost 60% of females were mature at 1+ age group. At ages over 2 years, all males and females were found to be mature. Batch fecundity (BF) of 33 females was related to standard length, and the relationship between standard length and BF was expressed by the exponential equation: BF = 269.5e^0.020954SL.     

Spawning of the Temperate Sea Cucumber,Australostichopus mollis (Levin)

The spawning of sea cucumbers is related to the interaction of environmental cues and reproductive maturity. Groups of Australostichopus mollis were collected every 2 wk during the summer reproductive season from mid‐October to early February. They were observed for spawning in the hatchery during heat‐shock trials conducted 3–5 C above ambient seawater temperature. Lunar periodicity existed with spawning being most prominent in the week following a full moon. In the week prior to a spawning event, there was also a decrease in ambient incoming seawater temperature. More than 75% individuals spawned during most trials in which spawning occurred. In total, 40% of the 270 individuals spawned during the reproductive season. Reliable spawners were females with a yellow gonad color and large numbers of vitellogenic oocytes, and males with large numbers of spermatocytes and an absence of motile spermatozoa. Furthermore, the percentage germinal vesicle breakdown of oocytes exposed to starfish radial nerve extract compared to seawater was greater for the more orange‐colored gonad of nonspawners. Gonad color is useful in determining the likelihood of spawning over a 2‐wk period in the presence of a cue. Sea cucumbers held for short periods in the hatchery during the reproductive season maintain a natural rhythm of spawning that can be monitored using visual indices and augmented using heat shock.