Reproductive strategies of two deep-sea gastropod species from the Porcupine Seabight (Northeast Atlantic)

Two species of small gastropods (<6 mm in length), Amphissa acutecostata (Philippi, 1844) and Gymnobela subaraneosa (Dautzenberg and Fischer, 1896), widely distributed in the northeast Atlantic, were found in large numbers in the Porcupine Seabight (Northeast Atlantic). Except for some aspects of taxonomy and distribution, as well as some data on larval development, the biology of these species is unknown. This study describes basic aspects of the life-history strategies of both species. Histological studies showed that oocyte and sperm development in both species was similar to the gametogenetic patterns observed in other deep-sea gastropods. In females, oogonia proliferated in the germinal epithelium and developed into previtellogenic oocytes (30–40 m), which grew into vitellogenic primary oocytes. Vitellogenic oocytes were covered by a thin layer of follicle cells involved in the vitellogenic processes. The maximum size for mature oocytes was 99.06 m for A. acutecostata and 114.82 m for G. subaraneosa. In A. acutecostata most of the volume of the ovary was occupied by previtellogenic and early vitellogenic oocytes, whereas in G. subaraneosa most of the volume was filled by large vitellogenic oocytes. Both species showed quasi-continuous production of oocytes. The oocyte size-frequency diagrams suggested a continuous release of a small number of oocytes throughout the year for A. acutecostata, and asynchronous periodic spawning events for G. subaraneosa. Gonad development and gametogenesis could be strongly affected by presence of parasites in one of the populations of G. subaraneosa.Communicated by J.P. Thorpe, Port Erin     

Growth and reproductive biology of the small penaeid shrimp Trachysalambria curvirostris in Tokyo Bay

We investigated the growth and reproductive biology of the penaeid shrimp Trachysalambria curvirostris in Tokyo Bay, Japan, by monthly bottom-trawl surveys from May 2002 to December 2004. We also examined oogenesis in T. curvirostris by histological observation of the ovary. Females grew faster and attained a larger body size for age than males. The growth rate was high in summer and low in winter and was likely to be associated with seasonal changes in water temperature. The carapace length (CL) at which 50% of females contained vitellogenic oocytes was estimated to be 17.0 mm. The reproductive season extended from May to October. Young-of-the-year appeared in October and could be traced across the months on CL histograms to the following September or October, indicating a 1-year life cycle. This extended reproductive season, together with our observation of asynchronous development of oocytes in the ovary, suggests that multiple spawning by individual females may occur during the reproductive season. Postovulated oocytes were not found among the samples we collected during the daytime, suggesting that final oocyte maturation and spawning occur at night. Cortical crypts in the cytoplasm of the oocyte, considered to be a general feature of oogenesis in penaeid shrimps, were not found in T. curvirostris, even in oocytes undergoing germinal vesicle breakdown. This result implies that the cortical reaction after spawning of T. curvirostris may be different from that of other penaeid shrimps.     

Reproductive ecology of <Emphasis Type="Italic">Fungiacyathus marenzelleri</Emphasis> from 4100 m depth in the northeast Pacific Ocean

Fungiacyathus marenzelleri (Vaughan, 1906) is a deep-water solitary coral, cosmopolitan in distribution that is found at depths of 300–6,328 m. This study examined gametogenesis, inter-annual variability and reproductive periodicity of F. marenzelleri collected from Station M (34°50′N, 123°00′W) in the northeast Pacific at a depth of 4,100 m. Samples were collected (May, June, October 1996; August 1998; February, June 2001; and June 2002) and histologically processed with spermatogenic stage, oocyte size and fecundity measured. Four stages of spermatogenesis were identified and all males contained multiple stages of sperm development in each seasonal sample. Three stages of oocyte development were identified; previtellogenic (<28–150 μm), vitellogenic (150–300 μm) and late vitellogenic (300–400 μm). Comparison of mean oocyte diameters among sampling dates showed there were no inter-annual variations or seasonal differences. Overall, fecundity was 1,290 (±407) oocytes polyp⁻¹, and with no significant differences between sample months. Fecundity was not polyp-size dependent. This study shows a similar quasi-continuous mode of reproduction to this species examined from the Northeast Atlantic Ocean, but the fecundity is reduced by 50%. The reproductive output may fluctuate in relation to the input of organic material at this site, as shown by non-significant trends in the oocyte size-frequency and fecundity data. A quasi-continuous output of gametes would promote successful fertilisation and wide dispersal of the lecithotrophic larvae.     

When fragmented coral spawn? Effect of size and timing on survivorship and fecundity of fragmentation in <Emphasis Type="Italic">Acropora formosa</Emphasis>

In order to determine competency of sexual reproduction and survival rate after fragmentation, the branching coral Acropora formosa was fragmented and fragments in three different sizes (ca. 5, 10 and 20 cm long) and three different stages of gametogenesis were transplanted on coral pavement. Their oocyte development and fecundity, as well as spawning were monitored for a 3-year period. The oocyte development was affected by both fragment size and by the developmental stage of oocytes when fragmented. In small fragments, the oocytes were resorbed while in large fragments they continued development. Oocytes in the early vitellogenic stage at the time of fragmentation were resorbed, whereas those in the late stage continued developing. Smaller fragments showed a lower survival rate and histological observations of their gonads revealed resorption of oocytes, suggesting that there was a trade-off of energy between reproduction and survival. Transplanted fragments often spawned one month earlier than the donor colonies in the first year, but spawning occurred in the same month as the donors or did not occur at all in the second year and none spawned in the third year. The risk of colony death may cause the fragments to re-allocate energy for sexual reproduction.     

Gonad morphology and oocyte development in<Emphasis Type="Italic"> Pseudocalanus</Emphasis> spp. in relation to spawning activity

Gonad maturation processes were studied in Pseudocalanus spp. females from Georges Bank and Cape Cod Bay (northwest Atlantic) using a combination of morphological analysis and experiments. For light microscopy of the oocytes, females of different maturation stages were preserved immediately after capture. The maturation processes during the spawning cycle were described from observations of live females which were exposed to feeding and starvation at two temperatures, 8 and 15°C, for 12 days. The gonad morphology of these females was examined in 24 h intervals, and spawning events were recorded. Both light microscopy and whole animal observation revealed that oocytes during maturation change in shape and size, in the morphology of the nucleus, and in the appearance of the ooplasm. Due to these modifications of oocyte morphology and due to oocyte migration, the morphology of the gonads changed distinctly during a spawning cycle. Five oocyte development stages were identified by light microscopy and related to a macroscopic system of four gonad development stages, that can be applied to whole animals and allows the identification of females ready to spawn. The experiment showed that food and temperature had strong effects on gonad maturation processes. High proportions of mature females were found when food was available, whereas the proportion of immature females increased shortly after exposure to starvation. Compared to 15°C, gonad maturation at 8°C was prolonged and thus spawning frequency was lower. The final maturation processes at food saturated conditions were slower than the embryonic development, and no indication was found that mature oocytes are stored in the diverticula waiting to be released. The duration of the interspawning interval would thus be determined by the duration of final oocyte maturation which is dependent on both temperature and food supply.Communicated by O. Kinne, Oldendorf/Luhe     

Dynamics of gonadosomatic index of fish with indeterminate fecundity between subsequent egg batches: application to Japanese anchovy Engraulis japonicus under captive conditions

The gonadosomatic index (GSI) is widely used as a simple measure of reproductive capacity, but its validity has often been questioned. This study showed the inter-spawning variation in the predicted GSI of Japanese anchovy using the gravimetric oocyte packing density method. Time course sampling showed that final oocyte maturation and subsequent ovulation occurred from afternoon to evening on the day of spawning. Oocyte in vitro assay, however, suggested that the timing of the spawning could be predetermined by midnight the day before spawning. Models predicted that the GSI of a female just after spawning gradually increases until the completion of germinal vesicle breakdown, after which it dramatically rises by 24–53 % per hour within a few hours of the onset of ovulation. This indicates that the predicted GSI of a female increases by 3.5 times within about 19 h before ovulation, even if the relative batch fecundity remains constant.     

Reproduction in the sea pen <Emphasis Type="Italic">Pennatula phosphorea</Emphasis> (Anthozoa: Pennatulacea) from the west coast of Scotland

Reproduction in the sea pen Pennatula phosphorea Linnaeus 1758 was investigated in a population located in southern Loch Linnhe, west Scotland. This was accomplished through analysis of trends in oocyte size-frequency distribution and fecundity over a 12-month period. Pennatula phosphorea is dioecious and the study population exhibited a sex ratio of 1:1. Oogenesis in female P. phosphorea is characterised by the maintenance of a large pool of small oocytes throughout the year of which a small proportion (<30%) mature synchronously and are broadcast-spawned during the summer months of July and/or August. Although spawning occurs annually, the duration of oogenesis exceeds 12 months. Initial oocyte generation is best described as ‘quasi-continuous’ as it may be suppressed during winter. The timing and periodicity of oogenesis and spawning may be related to seasonal environmental cues and it is proposed that annual spawning constitutes a brief and synchronous event. Fecundity is high in P. phosphorea, typically up to 50 oocytes per polyp and 40,000 oocytes per colony in medium to large colonies. Although mean polyp fecundity increased with colony size (axial rod length) there was no seasonal fluctuation in this measure of relative fecundity. Since only a small proportion of oocytes present are spawned each year, the present study advises caution when making inferences regarding the seasonal output of viable oocytes, especially on occasions where the definition of fecundity or the details of the oogenic cycle of a species are unclear. Pennatula phosphorea produces large oocytes (>500 μm), indicative of the production of lecithotrophic larvae; this may confer certain advantages with respect to larval longevity and survival.     

Length-structured analysis of the reproductive season of anchovy and common sardine off central southern Chile

The anchovy (Engraulis ringens) and common sardine (Strangomera bentincki) are two small pelagic fish which have a similar reproductive strategy off central southern Chile. The seasonal reproductive dynamics of both the species was investigated by taking into account the gonadosomatic index (GSI) and visual maturity data as a function of female size for the period 1993–1999, and also the seasonal pattern in condition factor per size classes. Larger females of common sardine (repeat spawners) have a reproductive peak earlier in the season than younger females at first maturity, while larger anchovy have a reproductive peak delayed as compared with first-time spawners. The condition factor of females exhibited an inverse cycle with the seasonal pattern of GSI, and delayed by approximately 6 months. Although larger females tend to present better and wider condition than smaller females, the condition of females seems to be delayed in larger females probably mediated by the seasonal pattern in food availability. This “energy storage strategy” in spring and summer time seems to be size-dependent and past energetic reserves could also affect the egg production and timing of reproduction. We concluded that the reproductive season of anchovy and common sardine is different and mediated by the length structure in the seasonal upwelling system off central southern Chile.     

Effects of temperature on oocyte growth in the Mediterranean terebellid Eupolymnia nuebulosa (Annelida: Polychaeta)

Eupolymnia nebulosa (Montagu) is a widely distributed terebellid polychaete that builds its tubes on the coastal shelf in areas with mixed soft and hard bottoms. From a long-term survey in the Bay of Banyuls, France (NW Mediterranean), we found an advancement of the timing of the spawning period coincident with a delayed breakdown of the thermocline. We postulate that persistent high temperatures can influence gamete development by stimulating oocyte growth, resulting in earlier spawning. During 1992 and 1993, we used a between-individuals experimental approach to assess the possible effect of temperature on oocyte growth based on: (1) determination of the growing fraction of the oocyte population (i.e. oocyte net growth); (2) identification of differences in oocyte growth-rate among females; (3) comparison of non-significantly different size-distributions of the growing oocyte fraction (net oocyte size-distributions) at the beginning of the experiments with those at the end. No effect of temperature on oocyte growth was detectable at the population level, but a positive individual response to prolonged high temperature was evident. Thus, the lack of a significant response by the population to prolonged high temperature does not imply a lack of individual response. We propose a model of oocyte-growth dynamics based on temperature that incorporates previous observations of extended oogenesis and oocyte growth during periods of both increasing and decreasing temperature and on the scattered pattern of oocyte size-distributions at the onset of spawning. Received: 4 November 1996 / Accepted: 18 January 1997     

Reproductive cycle of two populations of Ophionereis schayeri (Ophiuroidea) in New South Wales

Reproduction of two populations of Ophionereis schayeri (Müller and Troschel) in New South Wales was investigated from November 1991 through January 1993. The reproductive cycle was documented by histological examination of the gonads and by image analysis to determine the oocyte size-frequency distributions. Both populations of O. schayeri were mature in December and January and had a major summer spawning period between January and February. Thereafter, the condition of the gonads exhibited interindividual variability, with asynchronous low-intensity gamete release through August. O. schayeri has the potential to spawn for up to 8 mo of the year. This breeding pattern with synchronous spawning in summer and asynchronous gamete release through winter was similar in both populations. During autumn and winter, the gonads contained developing gametes and advanced gametes ready for spawning. The eggs spawned by O. schayeri during these seasons started their growth during the previous spring vitellogenic period, and continued to grow through summer. Upon reaching full size, they were stored for spawning outside the main breeding period. Spring is marked by increased spermatogenic and vitellogenic activity followed by maturation and spawning. Throughout their development, the oocytes of O. schayeri are surrounded by a follicle consisting of periodic acid-Schiff-positive (PAS+) haemal fluid and PAS+ yolk by the oocytes. In the testes, the haemal sinus projects into the centre of the spermatocyte columns, thus appearing to play a nutritive role in support of both oogenesis and spermatogenesis. Late vitellogenic oocytes of O. schayeri are firmly anchored to the germinal epithelium by an attachment complex consisting of specialised attachment cells and basophilic strands that radiate between the oolemma and the nucleus. Spawning is associated with rupture of the follicles, which remain as prominent, empty U-shaped profiles in the ovaries. O. schayeri produces copious numbers of 200 m-diam oocytes, suggesting that this species is a broadcast spawner and that it has a modified ophiopluteus or vitellaria larva.     

Zur sexuellen Differenzierung von Ophryotrocha puerilis (Polychaeta: Eunicidae)

Intact young males of Ophryotrocha puerilis Clap. Mecz. which are about to reach the female phase are capable of producing oocytes even under conditions of fasting. Intact isolated females may change sex under fasting conditions; their oocytes are not shed but resorbed. Decerebrated males which are about to reach the female phase at the moment of decerebration are unable to develop oocytes. Decerebrated females begin earlier with the production of spermatozoa than females under fasting conditions. The oocytes of decapitated females are either resorbed (young females with oocytes ranging in diameter up to 60 μm), or shed in egg masses capable of development after fertilization (older females with oocytes of 90 μm diameter or more). The effect of decerebration on females is compensated completely by implantation of isolated prostomia from female donors. Decerebrated males with implanted isolated prostomia from female donors immediately start oocyte production; these oocytes are not shed. In the majority of cases, decerebrated females change to the male phase after implantation of prostomia isolated from male donors. The mutual influence of a pair depends on direct contact of the partners. In isolated females, anterior fragments, consisting of prostomia and some segments, may induce change of sex and shedding of oocytes. On the other hand, intact females may induce sex reversal in anterior fragments. Even isolated prostomia from female donors may induce change of sex in intact females. A possible influence of intact females upon isolated prostomia was not found. Intact females and decerebrated females with implanted prostomia from female donors exhibit no mutual influence when placed together.     

Spawning pattern and type of fecundity in relation to ovarian allometry in the round herring <Emphasis Type="Italic">Etrumeus teres</Emphasis>

Spawning pattern (assessed by seasonal changes in ovarian developmental stages) and type of fecundity (assessed by analysis of oocyte-size frequency distributions) of the round herring Etrumeus teres were studied in relation to ovarian growth and seasonal changes in the gonadosomatic (GSI), hepatosomatic (HSI) and liposomatic (LSI) index as well as the somatic condition of spawners (CS) in a spawning ground of southern Japan. Except for summer, mature and recently spawned ovaries occurred all year round. Oogonia and primary oocytes were present in all ovaries, and cortical alveoli stage (CA) oocytes occurred in all mature, hydrated and partially spent (PS) females (PS: females containing post-ovulatory follicles). Before hydration, a clutch of larger yolked oocytes, undergoing synchronous growth (range 0.7–1.1 mm), was present in mature ovaries which was completely separated from a more heterogeneous clutch of oogonia, primary and secondary oocytes (<0.150 mm) and oocytes in the CA stage (range 0.15–0.60 mm). As vitellogenesis progressed, the yolked clutch increased in size but the CA oocytes remained arrested. The latter entered into the secondary growth phase when hydration started in the advanced batch. Ovarian growth was isometric in all developmental stages, validating the use of GSI, which showed a consistent monthly evolution among years. Spawning stopped in summer (July and August) and peaked in winter and spring. HSI correlated positively with GSI on both a monthly mean basis (r = 0.76) and individual fish basis (liver weight explained 67–83% of the variability in ovary weight when females were grouped into 1-unit GSI intervals) suggesting a significant role of liver in vitellogenesis. LSI and CS also showed marked seasonal changes peaking from summer to middle autumn. Overall results suggest that E. teres is a multiple spawner with a group-synchronous ovarian development and indeterminate annual fecundity, with the three processes linked to an isometric growth of the ovary. We propose that such a reproductive pattern is an adaptation to produce batches of large pelagic eggs through a protracted spawning season.     

Gonad morphology, sexual development, and colony composition in the obligate coral-dwelling damselfish Dascyllus aruanus

Gonad morphology and colony composition support the existing supposition that the obligate coral-dwelling damselfish Dascyllus aruanus has a protogynous hermaphroditic sexual pattern. Adults had either an active ovary containing vitellogenic oocytes, an ovotestis, or a spermiated testis and were classified as adult female, hermaphrodite, or adult male, respectively. Among individuals having male function, the testis (or testis portion of the ovotestis) takes the form of an unrestricted spermatogonial lobular testis. Among hermaphrodites having an ovotestis, a small proportion of individuals had a gonad in which both the ovarian and testicular portions were inactive (inactive hermaphrodites), whereas the majority had a predominantly testicular ovotestis that contained spermatozoa (male-active hermaphrodites). The size range of individuals within gonadal classes indicates that all D. aruanus first develop an ovariform gonad. Some individuals then undergo ovarian maturation to become adult females while others develop testicular tissue to form an ovotestis and become male-active hermaphrodites. Subsequently, progressive loss of ovarian tissue results in the development of a secondary testis from an ovotestis with the retention of a residual, afunctional lumen among adult males. The wide size range of individuals having an ovotestis suggests that some hermaphrodites function as adult females before developing testicular tissue while other individuals do not pass through an adult female stage. If this is the case, D. aruanus exhibits a diandric protogynous hermaphroditic sexual pattern. The apparent prolonged retention of an ovotestis with both healthy oocytes and an ovarian-type lumen in a spermiated ovotestis, as well as a functional sex ratio of 1:1 for adult females:adult males plus male-active hermaphrodites also raises the possibility that D. aruanus may be capable of bidirectional sex change during the hermaphroditic stage. Such a capability would be highly adaptive for a species having limited mobility and unpredictable recruitment of new colony members resulting in unpredictable mating opportunities.     

Maturation and diel reproductive periodicity of round scad (Carangidae: Decapterus punctatus)

The diel reproductive periodicity of Carangidae is poorly known but appears to be highly variable between species. Some species spawn during the day, others are believed to spawn at night, and it is demonstrated here that round scad, Decapterus punctatus, spawn at dusk. We collected D. punctatus in the eastern Gulf of Mexico during three April cruises (1995, 1996, and 1997). Based on histological criteria, size at 50% maturity was 113 mm fork length (FL) for males and 128 mm FL for females. The gonad-somatic index (GSI) of mature males was significantly different between hours and appeared to show diel periodicity. Diel periodicity was also observed in changes in female GSIs, whole oocyte diameters, and ovarian histology. The average GSI of mature females fluctuated two-fold between day and night, and the size distribution of whole oocytes in some fish was bimodal (at 0.3-0.4 and 0.7-0.8 mm diameter) at dusk rather than unimodal during most of the diel cycle. Histological preparations revealed that these rapid changes in ovarian GSIs and oocyte size distributions were the result of final oocyte maturation. Germinal vesicle migration was observed from 0900 to 1400 hours eastern standard time (EST), germinal vesicle breakdown was evident as early as 1100 hours EST, and ovulation occurred as early as 1800 hours EST. Spawning frequency (approximately every 5 days) was similar whether calculated from the proportion of females with hydrated oocytes during the afternoon or from the proportion of females with postovulatory follicles during the morning. Batch fecundity correlated with fish size and ranged from 5,500 to 34,700 hydrated eggs per individual. These findings do not support published hypotheses that young-of-the-year D. punctatus reproduce before their first winter or that D. punctatus reproductive output is bimodal within a year.     

Long-term changes in reproductive patterns of the holothurian<Emphasis Type="Italic"> Oneirophanta mutabilis</Emphasis> from the Porcupine Abyssal Plain

Time-series studies (1989–2002) in the NE Atlantic have shown large-scale changes in the composition and structure of the benthic community on the Porcupine Abyssal Plain. Radical changes in the abundance of some species in 1996 led to a significant shift in the way in which organic matter was reprocessed at the seabed. This article examines the reproductive processes of the holothurian Oneirophanta mutabilis collected during the time series. The reproductive biology of O. mutabilis is reviewed. No males were evident in any of the samples. The sex ratio (females: no gender) was biased significantly towards no-gender individuals. The maximum egg size was 650 m and there was no evidence of synchrony in reproduction. Significant changes in the oocyte-size distribution and the fecundity of O. mutabilis were noted through time, coinciding with the time of greatest faunal change in the benthic community. There was an increase in the proportion of previtellogenic oocytes and a decrease in the proportion of mature vitellogenic oocytes in 1997 and 1998, in parallel with a significant decrease in fecundity of the post-1996 samples. Samples from 2002 showed a reversal in the reproductive trends, with an increase in the proportion of mature vitellogenic oocytes and fecundity. The results are discussed in relation to large changes in abundance of the epibenthos on the Porcupine Abyssal Plain. It is suggested that the superabundance of certain megafaunal species on the abyssal seafloor affected the availability of trophic resources for O. mutabilis, leading to the changes in its reproductive effort.     

Ovary structure and oogenesis in Cirratulus cirratus (Polychaeta: Cirratulidae)

Oogenesis in polychaetes has, in most species, two main phases: a coelomic phase during which vitellogenesis occurs, and an ovarian phase. Details of the latter are known in very few species. Efficient reproduction requires coordination between these two phases of oocyte differentiation. The ovaries of Cirratulus cirratus (O. F. Müller) occur 2/segment throughout the fertile region of the body; 5 main stages of oocyte differentiation can be recognised on them: stem cells, oogonia, premeiotic oocytes, early oocytes and terminal oocytes. A quantitative study of the composition of the ovary throughout the reproductive cycle shows that the ovary size is approximately constant, but that the percentage of cells in the terminal oocyte stage is reduced to zero prior to spawning. This stage in oocyte differentiation is therefore a critical one, at which oogenesis may be arrested. The ovary alternates between a proliferative phase when the terminal oocytes are present, and a non-proliferative phase when they are absent. The overall rate of germ cell production for each ovary is low, less than 1 cell/ovary/day, and the, ovary tissue turnover time is greater than 2 years. A qualitative model describing the production of oocytes is presented, and the implications of the low rate of germ cell production are discussed. A low rate of germ cell proliferation, as in Cirratulus cirratus, implies that the rate of oocyte output into the coelom will be controlled by factors influencing the later stages of ovarian oocyte differentiation.     

Rapid changes in growth,condition, size and age of small pelagic fish in the Mediterranean

Since 2007, the ecosystem of the Gulf of Lions has shifted to a different regime, characterised by a low anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus) biomass and a remarkably high sprat (Sprattus sprattus) biomass. Surprisingly, the abundance and recruitment of anchovy and sardine remained high. To understand which processes (bottom-up or top-down control, etc.) could have caused this shift, we studied the changes in body condition, growth and size and age of anchovy, sardine and sprat over 1984–1985 and 1992–2012, using data from scientific surveys. The annual age structure of anchovy and sardine was estimated using Bayesian mixture models based on size frequency data with priors on the age–length relationship derived from independent otolith readings. The results indicated periods during which anchovy and sardine were in an average (1992–2004), good (2005–2007) or poor (2008–2012) overall state of condition. For sardine, the shift towards smaller fish observed during these past 4 years was explained by a combination of slower growth and the disappearance of older individuals (ages 2+). Despite the increase in biomass of sprat since 2008, indications were found that sprat was also smaller than in the past. As growth and condition decreased and overexploitation has not been documented or suspected for those three species in this area, we propose that the current decline in sardine and anchovy biomass could be due to qualitative and/or quantitative modifications in the planktonic production (i.e. a bottom-up control) or mass mortalities of adults due to an epidemic disease.     

Gametogenesis, spawning behavior, and early development in the “iceworm”Hesiocaeca methanicola (Polychaeta: Hesionidae) from methane hydrates in the Gulf of Mexico

Gametogenesis, spawning behavior, and early development have been described in the methane-seep polychaete Hesiocaecamethanicola Desbruyères and Toulmond, 1998, the first documentation of the reproductive biology of any cold-seep polychaete species. The worms were collected at the Green Canyon site in the Gulf of Mexico (27°44.77N; 91°13.33W) in August 1997. The gonads are situated in the neuropodia in association with an intraepithelial capillary system. Oogenesis is intraovarian, with oocytes remaining in the ovary until late vitellogenesis when they are released into the coelom for final growth and differentiation. Vitellogenesis involves both autosynthetic and heterosynthetic processes and, along with ovarian structure, suggests a relatively slow process of egg formation. Sperm differentiation is intertesticular until early spermiogenesis, when spermatid tetrads complete development in the coelom. The mature spermatozoon is an ect-aquasperm consisting of a tapering, digitate acrosome, a spherical nucleus, a midpiece containing from six to eight mitochondria and glycogen stores, and two centrioles associated with the flagellum. Both sexes undergo broadcast spawning, but the males spawn exclusively through the anus, a behavior previously unknown in polychaetes. Artificial fertilization resulted in spiral cleavage and development to the trochophore stage. Oocyte size-frequency analysis of adult females indicates a wide range of oocyte sizes and vitellogenic stages, suggesting that asynchronous gametogenesis occurs. Received: 13 July 2000 / Accepted: 29 November 2000     

Plasma sex steroid and vitellogenin profiles during gonad development in wild Mediterranean amberjack (<Emphasis Type="Italic">Seriola dumerilii</Emphasis>)

Mediterranean amberjacks, Seriola dumerilii Risso, were caught off the Pelagie Islands, in the south Mediterranean Sea, between May 1997 and June 1999. Fish blood was sampled, and gonads were collected at 10-day intervals throughout the spawning period and at monthly intervals during the resting period. Concentrations of plasma estradiol-17ß (E₂), testosterone (T), 17,20ß-dihydroxy-4-pregnen-3-one (DHP) and vitellogenin (Vtg) in females; and plasma T and 11-ketoT (11-KT) in males were correlated with changes in gonadal development. The first females that had already ovulated (F5) were found in late May. Most mature females (F4) were caught in June. Post-spawned females (F6) were found from late July until September. Estradiol-17ß was at baseline levels (<0.02 ng ml^–1) during autumn/winter and rapidly peaked (6.29±0.68 ng ml^–1) from May to early July. Plasma T levels showed a similar profile and were positively correlated to E₂ (r²=0.668) during the spawning period. Continuously elevated levels of E₂ and T were observed during the spawning season in vitellogenic females (stages F3, F4 and F5). Resting females were found during the autumn/winter months. Vitellogenin levels increased during May and peaked in June, reverting to undetectable levels in August, in parallel with sex steroid changes. Plasma DHP levels peaked in June (283.45±97.3 pg ml^–1), falling to basal values (<5 pg ml^–1) in August. DHP levels were higher in mature females (F4) than in maturing (F3) and in partially ovulated (F5) females. DHP values increased during germinal vesicle migration, peaked during germinal vesicle breakdown and decreased again during complete oocyte hydration. In males, changes in T and 11-KT plasma levels were related to testis development. The highest levels of T (5.76±2.64 ng ml^–1) were measured during spermatogenesis and highest 11-KT (5.28±3.6 ng ml^–1) in males with milt, from May to June. This study provides information, for the first time, on the relation between plasma sex steroid profiles and gonad development in wild Mediterranean amberjack, a useful benchmark for broodstock monitoring under controlled conditions.Communicated by R. Cattaneo-Vietti, Genova