A comparison of the reproductive cycles of Modiolus modiolus (L.), Cerastoderma (=Cardium) edule (L.), and Mytilus edulis L. in Strangford Lough,Northern Ireland

Summary This paper examines the reproductive cycles of three ecologically important marine bivalves-Modiolus modiolus (L.), Cerastoderma edule (L.), and Mytilus edulis L. in Strangford Lough, Northern Ireland over a period of almost five years.Whilst Modiolus does not appear to become sexually mature until it is several years old, Mytilus and Cerastoderma can reproduce in their first and second years of life respectively. In Cerastoderma and Modiolus sexual maturity is preceded by a period of rapid somatic growth.The subtidal Modiolus population remained in a more or less fully ripe condition virtually throughout the period of this investigation suggesting that this particular population lacked any marked cyclical reproductive activity. We interpret this as evidence of slow but almost continuous release of gametes throughout much of the year, a suggestion which is supported by recruitment data. A small intertidal population of Modiolus in Belfast Lough monitored over a period of two years exhibited a much more seasonal cycle. Here spawning occurred mainly during the autumn and winter. These data suggest that localised environmental factors are exceedingly important in controlling the annual reproductive cycle of this species. Cerastoderma from the mid-tidal sand flats ripened rapidly during the spring and spawned over a relatively restricted period in the summer. In Strangford Lough Mytilus occurs predominantly in the low-shore and while it spawns mainly in the spring and summer the annual cycle is considerably more protracted and variable than in Cerastoderma.Variations in the duration of the spawning periods in these bivalves can perhaps be explained in terms of both environmental stability and the immediate physical conditions experienced by these particular populations. The reproductive strategies exhibited by Cerastoderma, Modiolus, and Mytilus in Strangford Lough are considered in relation to population stability and to the different patterns of mortality which characterise these species in their respective local habitats.     

Biochemical and energy dynamics throughout the reproductive cycle of the striped venus Chamelea gallina (Mollusca,Bivalvia)

The striped venus Chamelea gallina is an important commercial bivalve species in Europe. However, large inter-annual fluctuations in stock abundance and periodic recruitment failure threaten the biological and economic sustainability of this fishery. This study aimed to improve the knowledge of the reproductive cycle and reproductive strategies of this species from the Algarve coast (southern Portugal) in order to contribute to the establishment of management measures and to assess its potential for aquaculture. The reproductive cycle of C. gallina followed a seasonal cycle, significantly influenced by sea surface temperature and food availability. Gametogenesis took place in winter, coinciding with the phytoplankton bloom. Spawning occurred during summer, followed by a short period of sexual inactivity in autumn. Condition index did not reflect the reproductive cycle of C. gallina and generally, followed the same trend of chlorophyll a. Glycogen was positively correlated with gonadal index and chlorophyll a. High total lipid values were recorded throughout gonad ripeness and spawning, but decreased at the end of the spawning and in the rest period. The extended spawning period of C. gallina will allow larvae to be obtained for much of the year by artificial spawning of wild broodstock.     

Seasonal variation in the biochemical composition of Mytilus viridis at Ratnagiri on the West Coast of India

1. The seasonal variation in the water, protein, fat and glycogen contents of the mussel, Mytilus viridis has been studied for the year March, 1974 to March, 1975.
2. The water level increased during the monsoon season and decreased in summer.
3. The level of protein, fat and glycogen showed correlation with the reproductive cycle of the mussel.
4. The protein level was high when the mussels were mature and dropped during the breeding period.
5. During sex change from male to female in May the protein level remained high whereas during sex change from female to male in October and November it was low.
6. The fat level was high in mature mussels and declined on spawning.
7. The glycogen level was at its peak in immature mussels and low in mature.

     

The annual reproductive cycle of the freshwater mussel Dreissena polymorpha Pallas in lakes

Summary The annual development of the gonads of Dreissena polymorpha was studied at three sampling sites in two lakes over 3 and 1 1/2 years, respectively. A resting stage occurred after the last spawning in summer/autumn. Oogenesis (accompanied by multiplying segmentation of the oogonia and early growth processes of its oocytes) restarted in specimens at least 1 year old at low temperatures (below 10° C) during winter and early spring. At one location (Fühlinger See) the onset of the spawning season was correlated with an increase of water temperatures above 12° C. At 2 m depth, two main spawning periods in May and August were normally recognized, the first at temperatures of 12–16° C, the second at 16–21° C. It was clearly demonstrated for the first time in Dreissena polymorpha that the oocytes became mature in successive cohorts within one gonad. A female mussel may spawn several times during the reproductive season. At 9 m depth, the onset of spawning also started at about 12° C; this occurred in late summer, with two spawning periods within 1 month at a temperature range of 12–16° C. At another location (Heider Bergsee) the size of the gonads and the oocytes was reduced during April of both years studied, when food supply was low simultaneously with rapidly rising water temperatures in this shallow lake. There was no spawning period during spring. The major spawning period was delayed until July (temperatures 19–22°C). This shows (1) the synchronizing influence of low winter temperatures on the annual reproductive cycle and (2) a temperature threshold of at least 12° C for the start of the spawning processes. The results are discussed with regard to the geographical limits of further spread of Dreissena polymorpha.     

The reproductive cycle and its control; frequency of spawning and fecundity in Blennius pholis L.

Spawning in Blennius pholis L. is seasonal occurring from March to July in the population of the South Gower beaches. There is evidence that both temperature and daylength regulate the reproductive cycle. Cyclical changes in the ovary during the reproductive cycle are studied by analysis of the changing size frequency distribution of the oocytes. Adults are capable of spawning a minimum of eight times in any one spawning season, and females > 11 cm in length have an estimated fecundity of 8,000 eggs.     

The recolonization potential of Metridium senile in an area previously depopulated by oxygen deficiency

Summary Every summer the deepest parts of the inner Flensburg fjord are subject to O₂-deficiency lasting from a few weeks to several months. In spring, however, populations of Metridium senile can be found in these areas, in spite of the fact that frequently the local anoxic period of the previous summer has been 2–3 times longer than their anoxia LD₅₀-value (3 wks).Responsible for this phenomenon is an intensive recolonization by adult Metridium during autumn and winter. This process has been investigated in an 8 months monitoring from May to December 1981. Results on the recolonization mechanism, the population structure of immigrating anemones and recolonization rate as a function of available hard substratum are presented.     

Reproductive tactics and development of sexually dimorphic structures in a stream-dwelling characid fish (Deuterodon stigmaturus) from Atlantic Forest

The reproductive tactics of Deuterodon stigmaturus were investigated in this study, testing whether the species presents a seasonal or opportunistic life-history strategy in a high latitude Atlantic Forest stream in Brazil. The relation between the development of anal-fin spinelets (sexually dimorphic structures in characids) and the reproductive period of D. stigmaturus was also investigated. The species displayed a seasonal life-history strategy, with the reproductive period occurring between austral spring and summer. The reproductive period was related to increase in temperature and photoperiod, corroborating several studies that suggest positive relation between seasonal reproduction and abiotic predictability. The data indicated total spawning occurring in January, coinciding with the month of greatest rainfall (historical and in the study year). However, the observation of postovulatory follicles in previous months suggests small spawning before January. The development of spinelets on the anal-fin was the only sexual dimorphic trait between males and females. Contrasting with several other studies, seasonal development of anal-fin spinelets was observed in adult males, following the reproductive period and regressing afterwards. Thus, some characid species probably retain this structure throughout the year and others do not, which may be related to life-history strategy differences.     

The composition and seasonal dynamics of the hemocyte cell population in the clams <Emphasis Type="Italic">Corbicula japonica</Emphasis> Prime (1864) of the Kievka River (the basin of the Sea of Japan)

The parameters of a hemocyte cell population were investigated in the bivalve mollusk Corbicula japonica of the Kievka River (the basin of the Sea of Japan) at four seasonal points corresponding to different stages of the reproductive cycle: (1) March (sexual rest); (2) May (gametogenesis); (3) July (spawning); and (4) November (the end of reproductive activity). Using light microscopy, we identified four cell morphotypes in the hemolymph: small and large hyalinocytes, as well as basophilic and eosinophilic granulocytes. Flow cytometry confirmed the structural heterogeneity of the cell population and allowed us to estimate the seasonal variability of the cell composition in C. japonica hemolymph. The total cell count in the mollusk hemolymph did not change significantly during the annual cycle and did not correlate with the average cell size of hemocytes. In March, May, and November, granulocytes dominated in the cell population (74.3 ± 2.9, 77.5 ± 3.5, and 86.7 ± 2.6%, respectively), while in July their relative content was reduced dramatically (37.2 ± 5.1%) causing a significant decrease of both the average cell size and granularity in circulation. Most likely, this is connected with the summer migration of mature eosinophilic granulocytes from the hemolymph to spawning gonads for resorption of the unspent sexual products, as well as to other internal organs for participation in digestion and to provide the immune defense against pathogens.     

The impact of fish spawning on metal and protein levels in gastrointestinal cytosol of indigenous European chub

The study presented here reports for the first time cytosolic metal and protein levels in the gastrointestinal tissue of field-collected European chub (Squalius cephalus), living in low metal-contaminated river section. In two sub-cellular fractions (untreated cytosol and heat-treated cytosol), isolated from the whole gastrointestinal tract of indigenous chubs collected during spawning (April/May 2006) and post-spawning period (September 2006), seasonal or gender related differences of trace metals and proteins were determined. In both fractions, cytosol and heat-treated cytosol, metal levels decrease as follows: Zn > Fe > Cu > Mn > Cd and are significantly higher during the spawning period. Besides that, the level of heat-sensitive proteins (metalloenzymes) in cytosolic fractions is also significantly higher during the spawning period in both male and female specimens. Higher condition indices of chubs in the spawning period imply higher feeding activity, energy reserves and recent growth of indigenous chubs. Metallothionein levels, determined in the heat-treated cytosol, are comparable in gastrointestinal tract of feral chubs collected in both seasons and confine the background metallothionein levels, on average 3 mg g⁻¹ wet tissue. Chub spawning has been identified as a confounding factor, having an impact on cytosolic metal and protein levels, presumably due to enhanced food supply (higher condition indices) and fish spawning (higher gonadosomatic indices in some male specimens).     

Seasonal variation in light-shade adaptation of natural populations of the symbiotic sea anemone Aiptasiapulchella (Carlgren, 1943) in Hawaii

The productivity and biomass parameters of the symbiotic anemone Aiptasia pulchella (Carlgren, 1943) from a shaded mangrove lagoon (maximum summer irradiance of 100 μE m⁻² · s⁻¹) and a sunlit reef flat (maximum summer irradiance of 1400 μE · m⁻² · s⁻¹) were examined in Hawaii. Light-shade adaptation was evident in the summer populations (1981) but not observed during the fall (1982). In the summer, zooxanthellae from the lagoon A. pulchella (shade anemones) contained 2.97 pg Chl a cell ⁻¹ and those from the reef flat (sun anemones) contained 1.70 pg Chl a · cell⁻¹; but Chl a : c₂ ratios were 2.5 in zooxanthellae from both shade and sun anemones. During the fall, there were no significant differences in Chl a and c₂ of zooxanthellae (2.25 pg Chl a · cell⁻¹) in shade and sun anemones, but Chl a : c₂ ratios averaged 3.9. During both seasons, shade anemones were larger and contained higher densities of zooxanthellae than sun anemones. In addition to differences between shade and sun habitats, there was localized photoadaptation of zooxanthellae within individual anemones due to microhabitat variations in ambient irradiance. Growth rates of zooxanthellae in A. pulchella differed in shade and sun anemones. Specific growth rates for zooxanthellae in situ were the same for shade populations in both summer and fall (0.016 day⁻¹). However, zooxanthellae in sun anemones grew four times faster in the fall (0.033 day⁻¹) than during the summer (0.008 day⁻¹). These results suggest that growth of zooxanthellae in these anemones was independent of ambient irradiance. Photosynthesis-irradiance (P-I) responses of shade and sun anemones during the summer showed that shade anemones had greater photosynthetic efficiencies (α) but lower photosynthetic capacities (P_max) than sun anemones. Dark-respiration rates of sun anemones were twice those obtained with shade anemones. In the fall, these populations of anemones did not exhibit P-I responses characteristic of light-shade adaptation. Both α and P_max of shade and sun anemones were higher in the fall, indicating that zooxanthellae in A. pulchella adapted to seasonal reduction in irradiance.     

Reproductive cycle in female Waigieu seaperch (Psammoperca waigiensis) reared under different salinity levels and the effects of dopamine antagonist on steroid hormone levels

Waigieu seaperch (Psammoperca waigiensis) is a tropical marine finfish species, which may inhabit wide range of salinity during the entire life cycle. Regardless of the wide salinity tolerance, little is known about how salinity may influence the reproductive endocrinology of this important tropical species. In the present study, we investigated the seasonal variations in steroid hormone levels, oocyte maturation (OM) and ovulation in fish reared under different salinity levels. In addition, we investigated the effects a dopamine antagonist (domperidone: DOM) during the peak spawning period. Mature brood fish at 3 years old were cultured in four different salinities of 5, 10, 20 and 30‰ (part per thousand, ppt) from March to December 2007. Blood samples were collected monthly and key steroid hormones (testosterone (T), 11-ketotestosterone (11-KT), 17β-estradiol (E2) and progesterone (P)) levels in female fish plasma were analyzed using enzyme immunoassay method. OM, ovulation and several reproductive performance indexes were evaluated twice per month during the breeding season. Plasma hormone analysis showed significant differences in fish groups cultured in different salinities during the seasonal cycle. The gonadosomatic index (GSI) gradually increased from March, peaking in July at 10 and 30‰, and then decreased thereafter until December. Plasma steroid levels (E2, T, 11-KT and P) were observed in variable concentrations during the spawning period and showed monthly fluctuations that were apparently salinity dependent during on and off-seasons. Interestingly, 11-KT levels were found in small amounts in female fish and peaked in September at salinities of 10 and 20‰. DOM exposure produced significant differences in steroid hormone levels that were apparently dependent on dose, exposure time and the individual hormone. The present study indicated that holding Waigieu seaperch brood fish in different salinities during the breeding season produced significant effects on gonadal development and spawning incidences. The first spawning was observed on 8th of April for all groups after 100% water exchange at night. No significant differences of absolute and relative fecundity were observed between groups. Fish held at 10 ppt salinity during the breeding season spawned naturally, but maturity and spawning rates were reduced and no hatching was observed at the same salinity. Fish holding at 5‰ resulted to 100% mortality in brood fish. This indicated that salinity limits for oocyte maturation or ovulation and subsequent reduction in spawning, but embryonic development requires a higher salinity. The effect of salinity on embryo development and hatching rate suggests that in breeding season the brood fish spawned in areas where the salinity and other parameters are favorable.     

Oogonial proliferation and early oocyte dynamics during the reproductive cycle of two Clupeiform fish species

Although oogonial proliferation continues in mature females in most teleosts, its dynamics and the transformation of oogonia to early meiotic oocytes during the reproductive cycle have received little attention. In the present study, early oogenesis was examined throughout the reproductive cycle in two Clupeiform fishes, the Mediterranean sardine, Sardina pilchardus, and the European anchovy, Engraulis encrasicolus. Observations using confocal laser scanning microscopy (CLSM) provided extensive information on markers of oogonial proliferation (mitotic divisions, oogonia nests) and meiotic prophase I divisions of oocyte nests (leptotene, zygotene, pachytene, diplotene) in ovaries of different reproductive phases. In sardine, oogonial proliferation persisted throughout the entire reproductive cycle, whereas in anchovy, it was more pronounced prior to (developing ovaries) and after (resting ovaries) the spawning period. Anchovy exhibited a higher rate of meiotic activity in developing ovaries, whereas sardine exhibited a higher rate in resting ovaries. The observed differences between the two species can potentially be attributed to different seasonal patterns of energy allocation to reproduction and the synchronization between feeding and the spawning season.     

Gametogenesis, spawning and fecundity of Platygyra daedalea (Scleractinia) on equatorial reefs in Kenya

The reproductive ecology of the hermaphroditic broadcast spawning scleractinian reef coral Platygyra daedalea was studied on lagoonal reefs in Kenya. While single annual gametogenic cycles occurred in 84% of colonies, biannual gametogenic cycles were recorded in 16% of colonies and these patterns occurred in two morphotypes. In colonies with a single annual cycle, oogenesis occurred for 6–7 months from September to March and spermatogenesis for 5 months from November to March. In biannually spawning colonies, oogenic cycles overlapped for at least 2 months prior to gamete release. The major spawning period occurred in February and March, with minor spawning also occurring in August–October in biannually spawning colonies. Reproductive effort was lower during the minor winter compared to the major summer spawning, with fewer colonies reproducing (12.5–19.2%), not all mesenteries producing oocytes (32.5%) and less than half of the mesenteries with mature oocytes had associated spermaries (48.1%).     

Reproductive biology of the sea anemone shrimp Periclimenes rathbunae (Caridea,Palaemonidae, Pontoniinae), from the Caribbean coast of Costa Rica

Caridean shrimps are a highly diverse group and many species form symbiotic relationships with different marine invertebrates. Periclimenes rathbunae is a brightly colored shrimp that lives predominantly in association with sea anemones. Information about the reproductive ecology of the species is scarce. Therefore, we collected 70 ovigerous females inhabiting the sun sea anemone Stichodactyla helianthus in coral reefs from the southern Caribbean coast of Costa Rica. Females produced on average 289 ± 120 embryos. The volume of recently-produced embryos was on average 0.038 mm³, and embryo volume increased by 192% during the incubation period. The average embryo mortality during embryogenesis was 24%. The reproductive output was 0.24 ± 0.094, considerably higher than in many other pontoniine shrimps. Females carrying embryos close to hatching showed fully developed ovaries, suggesting consecutive spawning. We assume that the sheltered habitat, living on sea anemones, allows Periclimenes rathbunae to allocate more energy in embryo production than most other free-living caridean shrimps. This is the first record of Periclimenes rathbunae for Costa Rica.     

Seasonal changes in testis weight and testosterone concentration in the european wild boar (Sus scrofa L.)

The male reproductive cycle in the European wild boar (Sus scrofa) was characterized in free-ranging and captive animals. Puberty is attained at 10 months of age when testis weight averages 53 g. Thereafter, the sexual function follows a clearly marked seasonal pattern. In mature animals, testicular weight and related plasma testosterone levels were significantly higher in winter than during the summer months. These variations parallel the seasonal sexual activity of females. The results are discussed with emphasis on the possible role of daylength in seasonal changes of testicular function.     

Seasonal aspects of life cycles in Calathus melanocephalus and C. micropterus (Coleoptera, Carabidae) in the northern taiga

The seasonal dynamics of the activity and the demographic structure of Calathus melanocephalus and C. micropterus populations were studied in the northern taiga of Arkhangelsk Province. The period of adult activity lasts from early June to mid-or late September with the maximum surface activity observed in the middle of summer. In C. melanocephalus, mature individuals are recorded from early June to early September, and in C. micropterus, during the entire season. The data on seasonal changes of the demographic structure of the population demonstrate that in the northern taiga, these species probably possess a biennial life cycle with summer reproduction. The geographical variability of the demographic structure of populations and of life cycles of two species of the genus Calathus was demonstrated. Northwards from the south, the period of activity decreases and the period of reproduction increases and shifts from autumn to the middle of summer. A hypothesis was formulated, according to which in the species studied the annual life cycle in the central part of the range is replaced by the biennial cycle in the north.     

Reproductive cycles in oregon populations of the echlnoid, Strongylocentrotvs purpuratus (Stimpson). I. Annual gonad growth and ovarian gametogenic cycles

Four annual reproductive cycles were followed in the echinoid, Strongylocentrotus purpuratus (Stimpson), at three places on the central Oregon coast near 44°45′N lat., where intermittent upwelling depresses coastal sea temperatures from June through September. Monthly measurements were made of the gonad index of samples of 30 urchins and the relative frequency of five stages in oogenesis were determined from sectioned ovaries from these samples.Individuals in these populations are synchronous in their annual cycle of gonad growth, oogenesis, and spawning, the latter taking place between late December and March. The population usually undergoes one major, complete spawning within a period of 30 days. When large reserves of stored nutrients are present, ova continue to mature over a longer period and may be present in quantity from December into April. Gonad weight does not change significantly from March through June. From July through November the gonad undergoes its annual growth at a mean instantaneous relative growth rate of ≈ 1 % per day. Gonad growth is not significantly correlated with sea temperature. Variable temperatures resulting from upwelling do not result in erratic fluctuations in the reproductive cycle, probably because of the annual change in feeding rate, the seasonal shift in energy utilization, and the constancy of the amount of food assimilated during gonad growth. Gonad size and annual growth rates may differ significantly between years and locations, indicating that both are influenced by local environmental factors, probably food availability and degree of wave action.The frequency of oogonial clusters is least in mid-winter, increases after spawning, reaches an annual maximum in June and declines in the fall. Primary oocyte growth is very slow until October, when it increases abruptly, and some oocytes become ova as early as late October. When stored nutrients are low, many oocytes do not complete growth by January, and are not spawned until May. Prolongation of the spawning period delays the increase in frequency of oogonial clusters in the following new cycle. The timing of the annual increase in oogonial cluster frequency and of the onset of rapid oocyte growth did not otherwise vary between places and years. In these populations, entrainment or synchronization of the reproductive cycle to seasonal environmental events probably occurs at the beginning of one or all of these critical annual events: oogonial proliferation, annual gonad growth and rapid oocyte growth.     

Structure of the ellipsoid sheath in the spleen of the armadillo (Dasypus novemcinctus). A light and electron microscopic study

A seasonal study of the seminal vesicles in relation to that of the testes had been conducted in the catfish, H. fossilis. The annual reproductive cycle of the catfish has been divided into (i) Preparatory period (February–April), (ii) Prespawning period (May–June), (iii) Spawning period (July–August) and (iv) Postspawning period (September–January). Testes exhibit initiation of spermatogenesis in the mid-preparatory period, but significant increase in weight of the testes accompanied by active spermatogenesis occurs during the prespawning period. In the spawning period, the testes are maximally enlarged and their seminiferous tubules are packed with spermatozoa. Following spawning, the testes gradually regress in the postspawning period. The seminal vesicles show initiation of secretory activity during the preparatory period but their recrudescence lags behind that of the testes by about a month. The seminal vesicles attain maximum weight and secretory activity during the spawning period. Thereafter, the seminal vesicles regress precipitously and sooner than the testes. The histochemical and biochemical studies on the seminal vesicles indicate that the secretion contains mucoproteins, acid mucopolysaccharides, primary proteoses, besides traces of phospholipids and native proteins.     

Seasonal patterns of winter flounder Pseudopleuronectes americanus abundance and reproductive condition on the New York Bight continental shelf

To resolve varied and sometimes conflicting accounts of spawning and habitat characteristics for winter flounder Pseudopleuronectes americanus, seasonal patterns in abundance and reproductive condition were investigated in the New York Bight, near the southern edge of their current reproductive range. Fish were collected from trawl surveys on the inner continental shelf from October 2006 to October 2007. Pseudopleuronectes americanus were most abundant during January and April surveys, were rarely collected in August, with intermediate abundances in June and October. Measurements of fish condition [hepato‐somatic index (I_H), condition factor (K) and the per cent dry mass of muscle tissue (%M_D)] and reproductive condition [gonado‐somatic index (I_G)] were determined to evaluate seasonal changes in energy accumulation and depletion and reproduction. Males and females had similar patterns in body and reproductive condition, although the magnitude of change was greater for females. I_H values were highest during spring and early summer, suggesting increased feeding following spawning. K and %M_D increased through spring and summer then declined in the autumn and winter concurrent with gonadal development. Gonads began developing in the autumn, and in January, I_G values approached spawning levels, with many spent individuals collected in spring. Within these general patterns, however, there was a large degree of variability among individuals, and a few mature non‐reproductive (‘skipped spawning’) females were observed. In the period after spawning, increased energy intake, indicated by increased I_H, may influence reproductive output since this energy is gradually transferred to the muscle and used for gonadal development in the forthcoming year. The occurrence of ripening individuals on the inner continental shelf in January suggests that these fish either rapidly move into estuaries to spawn by February–March or they remain on the inner shelf to spawn, or some combination of these. Future studies should evaluate these possibilities, as both estuarine and inner shelf habitats are potentially affected by activities such as dredging, sand dredging and wind energy development.