Reproductive cycles in oregon populations of the echinoid, Strongylocentrotus purpvratus (Stimpson). II. Seasonal changes in oocyte growth and in abundance of gametogenic stages in the ovary

During the annual reproductive cycle in the echinoid, Strongylocentrotus purpuratus (Stimpson) two major seasonal events in oogenesis have been demonstrated by several different quantitative methods. Both seasonal changes in size and frequency distributions of stages of the oocytes indicate that in the intertidal populations studied, there is an abrupt increase in the growth rate of oocytes during October, accompanied by an increase in the rate at which oogonia become primary oocytes. Between March, just after spawning is completed, and October, oocytes increase in volume at a rate of ≈ 2 % per day. In October and November, the growth rate of oocytes approaches 6 % per day, and thereafter declines for oocytes reaching maturity in December.The absolute numbers of oocytes and oogonial clusters/mm² of ovary wall were estimated and adjusted for changes produced by volume changes in the gonad. The lowest numbers of oogonial clusters occur from December to March. Renewed proliferation begins soon after spawning. There is a significant increase in number of clusters in March, and the absolute cluster number increases to a maximum in June, reaching approximately four times the initial number. The proliferation rate during this period is ≈ 180 clusters/mm²/month; some proliferation continues into September. The number of small oocytes present remains the same from March to August, when it begins to increase. The total number of oocytes produced during the fall period is approximately three times the number initially present at the start of the annual cycle in March. Two populations studied differ in the absolute numbers of oogonial clusters and oocytes produced in the annual cycle; environmental factors must influence the processes involved. In S. purpuratus the large majority of oocytes differentiate from oogonia during the same reproductive cycle in which they reach maturity as ova.     

An analysis of the reproductive pattern in the sea star Astropecten irregularis (Pennant) from the Bristol Channel

Summary

The reproductive cycle in Astropecten irregularis is described, making use of a range of statistical techniques detailed previously. Analysis of gonad weights proved more satisfactory than the use of gonad indices, as the latter are not independent of animal size. When examining the course of oogenesis, standardised residuals in an (R × C) contingency table are much easier to interpret than size/frequency polygons.

The species has an annual cycle with spawning in June or July, but the gonads are small even when the animals are gravid, and the annual cycle in gonad weights is more marked in males. Proliferation of oogonia may apparently occur at any time of year, and the ripe ovary contains many small, previtellogenic oocytes. There is an annual cycle of small magnitude in the size of the pyloric caecum, with a peak in December.     

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.     

Gonad development and size‐at‐maturity of silver therapon Leiopotherapon plumbeus (Kner 1864; Teleostei:Terapontidae) in tropical volcanic lakes in south Luzon,Philippines

Gonad development of the silver therapon Leiopotherapon plumbeus in two volcanic crater  lake  habitats (Sampaloc Lake, Taal Lake) in south Luzon, Philippines was examined during the annual reproductive cycle. The minimum body size‐at‐maturity of fish in these two lake habitats was also compared. Four gonad development stages were characterized as basis for the classification of ovarian (immature, maturing, mature, spawned) and testicular maturation (immature, maturing, mature) phases. The occurrence of all development stages in individual gonads suggest an asynchronous development whereby advanced stages are recruited continuously from a pool of younger stage germ cells to result in elevated female and male GSI throughout the annual cycle due to active gonadogenesis. Together with the increasing occurrence of advanced stage oocytes and spermatozoa from March until October, the elevated GSI of fish may indicate peak gonadal growth during the onset of the dry season (December–January) for eventual spawning from the beginning (May–June) until the end of the wet season (October–November). In both lake habitats, male fish were smaller than females but, regardless of sex, the minimum size‐at‐maturity of fish in Sampaloc Lake was significantly smaller than fish in Taal Lake. Overall, asynchronous development during oogenesis and spermatogenesis allows for year‐round reproduction of silver therapon, with elevated gonad growth in the dry season in preparation for spawning during the wet season. Compared with fish in Taal Lake, a smaller size‐at‐maturity of fish in Sampaloc Lake may be a response of the wild fishery stock to long‐term high fishing mortality and degradation of the lake habitat.     

Sexual cycle and seasonal changes in the ovary of the red mullet, Mullus surmuletus, from the southern coast of Brittany

The reproductive cycle of the red mullet is described on a macroscopic scale in terms of the GSI, HSI and K , and on a microscopic scale in terms of histological changes in the ovary and changes in the oocyte size frequency distribution. On the southern coast of Brittany the red mullet breeds in May and June. During oogenesis, the previtellogenic period lasts 6 months and the secondary phase of vitellogenesis no more than 3 months. When spawning commences the process of vitellogenesis ceases and up to 20% of the vitellogenic oocytes become atretic. Prior to spawning a single batch of oocytes can be seen to be entering secondary vitellogenesis. During the immediate prespawning and spawning periods the existing vitellogenic oocytes mature but there is no recruitment from the stock of previteilogenic oocytes. This results in a gap or hiatus in the oocyte size frequency distribution between previtellogenic and vitellogenic oocytes within which there are very few resting or maturing oocytes. The red mullet appears to be a determinate spawner, in which egg loss through atresia considerably reduces the potential fecundity.     

Reproductive strategy of the Patagonian catfish Hatcheria macraei

This study describes the reproductive strategy of the stream‐dwelling catfish Hatcheria macraei in the Pichileufu River, Argentina. Gonad maturity phases, classified on the basis of histological analysis, stages of gamete development and the frequency distribution of oocyte size, were correlated with macroscopic features of the gonads. Hatcheria macraei has a cystovarian ovary, asynchronous oocyte development and lobular testes. Five oocyte and four spermatogenic stages were identified and related to macroscopic gonad characteristics, making it possible to divide gonad development into five phases for females and males. Mature oocyte diameter ranged from 922 to 1935 µm. Absolute fecundity in mature females varied from 115 to 480 oocytes. Hatcheria macraei has multiple spawning during a protracted reproductive season that extends from December to April. This, together with its small size, is characteristic of an opportunistic reproductive strategy, commonly found in species that inhabit adverse and unpredictable environments, such as the low‐order rivers of Patagonia.     

The reproductive biology of the horse mackerel Trachurus trachurs (L.) in the North Sea and English Channel

In the horse mackerel the gametes develop asynchronously and are released in batches. The maturity cycle is characterized by a rapid post-spawning recovery period and a relatively long period of oocyte maturation. Mean gonad weight reached a peak in June and intraovarian hyaline oocytes occurred from May to August. Determination of fecundity was complicated by resorption of oocytes both before and after spawning, and by the fact that resting and developing oocytes were not clearly separated by size. An estimate of'potential fecundity'was obtained by a combination of histology and oocyte measurement. Plankton surveys showed that a major spawning area exists in the Southern Bight of the North Sea, with eggs occurring from May to late August. An estimate of annual egg production was combined with the fecundity data to give an estimate of stock size of about 500 000 tons.     

Oogenesis of Perinereis macropus Claparede, 1870 (Annelida, Polychaeta) in the Gulf of Gabes (Tunisia)

The polychaete Perinereis macropus (Claparède, 1870) (Nereididae) is present in the Gulf of Gabes, but its reproductive biology is unknown. An intensive study was conducted from August 2004 to July 2005 to characterize the life cycle of a population in the mouth of wadi Ferd in Gabes. The examination of sexual products allows us to describe the morphological oocytes aspects at different stages. The results show that P. macropus has an asynchronous oogenesis. Moreover, the biometric study of oocytes growth allows us to clarify the female sexual cycle. The female maturity occurs in April and the mature oocyte diameter is approximately 250+/-32.67 microm. However, spawning occurs in May, when the seawater temperature starts rising. We propose that the reproductive season stretches from March to June in the Gulf of Gabes.     

Gonad morphology,oocyte development and spawning cycle of the calanoid copepod <Emphasis Type="Italic">Acartia clausi</Emphasis>

Information on gonad morphology and its relation to basic reproductive parameters such as clutch size and spawning frequency is lacking for Acartia clausi, a dominant calanoid copepod of the North Sea. To fill this gap, females of this species were sampled at Helgoland Roads from mid March to late May 2001. Gonad structure and oogenesis were studied using a combination of histology and whole-body-analysis. In addition, clutch size and spawning frequency were determined in incubation experiments, during which individual females were monitored at short intervals for 8 and 12 h, respectively. The histological analysis revealed that the ovary of A. clausi is w-shaped with two distinct tips pointing posteriorly. It is slightly different from that of other Acartia species and of other copepod taxa. From the ovary, two anterior diverticula extend into the head region, and two posterior diverticula extend to the genital opening in the abdomen. Developing oocytes change in shape and size, and in the appearance of the nucleus and the ooplasm. Based on these morphological characteristics, different oocyte development stages (OS) were identified. Mitotically dividing oogonia and young oocytes (OS 0) were restricted to the ovary, whereas vitellogenic oocytes (OS 1–4) were present in the diverticula. The development stage of the oocytes increased with distance to the ovary in both, anterior and posterior diverticula. Most advanced oocytes were situated ventrally, and their number varied between 1 and 18, at a median of 4. All oocyte development stages co-occur indicating that oogenesis in A. clausi is a continuous process. These morphological features reflect the reproductive traits of this species. In accordance with the low numbers of mature oocytes in the gonads, females usually produced small clutches of one to five eggs. Clutches were released throughout the entire observation period at intervals of 90 min (median) resulting in mean egg production rates of 18–28 eggs female⁻¹ day⁻¹.     

Testing for the Effects of Seasonal and Lunar Periodicity on the Reproduction of the Edible Sea Urchin <Emphasis Type="Italic">Tripneustes gratilla</Emphasis> (L) in Kenyan Coral Reef Lagoons

The annual and lunar reproductive cycle of the widely distributed edible sea urchin Tripneustes gratilla (L) was examined through measurements of gonad index, histological examination of gametogenesis, and induction of spawning with KCl injections. The population density and morphological characteristics of urchins at Diani, Kanamai, and Vipingo reef lagoons were also studied as well as the effects of seawater temperature and light on reproduction. Gonad growth started early during the northeast monsoon and reached a peak in June at the beginning of the southeast monsoon followed by a sharp decrease in gonad size of 50% in July and August towards the end of the southeast monsoons. Histological examination of gonads, revealed many different stages of gametogenesis with gametes present throughout the year, indicating continuous reproduction. There was a significant relationship between gonad index and lunar day with spawning occurring between lunar day 7 and 21, but spawning was not in perfect synchrony in the population. The population density of urchins at each reef is variable from year to year and was highest on average at Vipingo. Urchins at Kanamai had the lowest gonad indices, the largest jaws and smallest individuals an indication of food limitation. The gonads (roe) of T. gratilla at all three sites, were perpetually ‘runny’ an attribute that is not suitable for urchin fisheries. Studies to develop techniques to improve roe quality are recommended.     

Reproductive patterns of the Pacific oyster Crassostrea gigas in France

Summary

In France, national management programs focus research on understanding reproductive factors in Crassostrea gigas to confront problems of the oyster industry. However, little information has been documented in which reproductive patterns include sexual changes. The reproductive cycle of oysters at three sites of the Atlantic coast of France was examined from 1996 to 1998, and the seasonal variations in oocyte size-frequencies, and sex ratio were described. The results showed a synchronism within the population concerning reproductive behavior. Young oocytes are generated after spawning and show no apparent changes during winter. Growth of oocytes begins in spring and cells reach maturity in April-May and are ready for a single spawning season in June-July. Oocytes that were not released during spawning are reabsorbed within the gonad. The significant difference between sites is that spawning occurred 1 month later in the southern area. A modal analysis showed that oocyte populations in the sample individuals are primordially bimodal, but with polymodal occurrences in June-July, in some cases. Irregular alternative sexuality was detected at all sites, and hermaphrodites appear to be a transition phase that allows changes from male to female during early spring. Previous observations, together with the study of the development of oocyte cohorts over time, permit a hypothetical model concerning the kinetics of gametogenesis in C. gigas. The model suggests that primary oocytes are generated from energy supplied from degenerating, as well as young oocytes that do not reach the mature stage within the gonad during autumn-winter. It seems that, during vitellogenesis, there is disintegration of smaller cells coupled with transfer of energy to the larger oocytes, which continue to grow and mature.     

Histological studies on early oogenesis in barfin flounder (Verasper moseri)

There is much information on oogenesis from the resumption of the first meiotic division to oocyte maturation in many vertebrates; however, there have been very few studies on early oogenesis from oogonial proliferation to the initiation of meiosis. In the present study, we investigated the histological changes during early oogenesis in barfin flounder (Verasper moseri). In fish with a total length (TL) of 50mm (TL 50mm fish), active oogonial proliferation was observed. In TL 60mm fish, oocytes with synaptonemal complexes were observed. Before the initiation of active oogonial proliferation, somatic cells which surrounded a few oogonial germ cells, started to proliferate to form the oogonial cysts that accompanied oogonial proliferation. In TL 70mm fish, however, the cyst structure of the oocyte was gradually broken by the invagination of somatic cells, and finally the oocyte became a single cell surrounded by follicle cells. Upon comparison of nuclear size, DNA-synthesizing germ cells could be divided into two types: small nuclear cells and large nuclear cells. Based on histological observation, we propose that the small nuclear cells were in the mitotic prophase of oogonia and the large nuclear cells were in the meiotic prophase of oocytes, and that the nuclear size increases upon the initiation of meiosis.     

Aspects of the reproductive biology of the grouper, Epinephelus tauvina (Forskål), in Kuwaiti waters

Gonad maturation in Epinephelus tauvina is examined over one annual reproductive cycle. The species has one major spawning period from April to May and this is associated with increasing water temperatures and relatively low salinity. The histological changes in the gonads in the female, male and transitional phase are examined, and oogenesis and spermatogenesis are described in five developmental stages. That E. tauvina is a protogynous hermaphrodite is confirmed, and sexual transition is found to occur in individuals 55–75 cm in length, and is related to spawning activity. Fecundity estimates for E. tauvina of length 35.1–62.3 cm ranged from 850 186 to 2 904 921.     

Maturity and gonad changes of Oreochromis (Nyasalapia) karongae raised in fish ponds in Malawi

The reproductive biology of pond-raised Oreochromis (Nyasalapia) karongae was investigated. Gonad histology and gonadosomatic indices (GSIs) indicated a potential for multiple spawning in a season. Several peaks of oocyte-size distribution and several maturation stages occurred in the same gonad. GSIs of 2.5% and 1.4% were recorded in female and male fish, respectively. Three stages of oocyte maturation (primary growth, formation of yolk vesicles, vitellogenesis) and three stages of sperm development (spermatogonia, spermatid, spermatozoa) were observed. With the exception of the final maturation stage, all development phases seemed to proceed satisfactorily. The final stage of maturation was attained at oocyte size of 2.70 ± 0.54 mm and was selectively impaired in some female fish by a lack of deposition of vitellogenin. This abnormal condition led to atrophic oocytes lacking yolk granules and vesicles. Sexual maturation was attained at a relatively large size of 16.0 cm (114 g) compared with other tilapia of the mossambicoid group (i.e. Oreochromis mossambicus and Oreochromis shiranus ). A combination of gravimetric and histological techniques was successful in charting gonad changes and calibrating external against internal gonad features.     

Morphological and gonadal assessments from historical collections of Bluenose Shiners Pteronotropis welaka

Management and conservation have begun to rely on supplemental information to make appropriate decisions. In organisms with little available information, preserved specimens may be particularly important for researchers to continue their role in the management process. Bluenose Shiners are a minnow species that can benefit from such analyses as they are of conservation concern across their native range in the Southeastern United States. To supplement conservation, the objectives were to: (a) quantify sexual dimorphism through a comprehensive morphological analysis, (b) approximate peak spawning condition of males and females through GSI measurements over the anticipated spawning season, and (c) utilize female gonad histology to refine conclusions regarding spawning condition from GSI. Historical collections of Bluenose Shiners obtained from the Tulane University Biodiversity Research Institute were used to conduct morphological and gonadal analyses. While males expressed all morphometrics to a greater degree, male dorsal and anal fin length appears to be the most distinguished characteristic beginning at a total length of approximately 45 mm. GSI displayed peaks in the samples from April 21, 1957 and June 1, 1968; female GSI from Black Creek, MS in April, May, and June of 1986 suggested a peak in late May. Gonad histology showed a progression towards final oocyte maturation through May to early June, via relative prevalence of stage IV and absence of stage I oocytes. This information can be used to supplement future morphometric analyses and reproductive studies performed on Bluenose Shiners or other fish species.     

Storage and reproductive strategy of the carpet-shell clam,Ruditapes decussatus in the Gulf of Gabès (Tunisia)

In this study, the variations of glycogen concentrations in Ruditapes decussatus from Sfax coasts (Tunisia) were described in relation to the reproductive cycle. Separate analyses were made of gonad, adductor muscle and ‘remainder’. The timing of gametogenic development and spawning was evaluated using qualitative histology associated with image analysis including (1) the estimation of the gonadal occupation index (GOI), (2) surface area occupied by reserve tissues and (3) variation in oocyte diameter. The reproductive cycle of R. decussatus exhibited partial asynchronization between sexes, the major difference being observed in the duration of the spawning period. Contrary to previous studies, we observed continuous partial spawning (e.g. 50% of ripe oocytes still subsisted at the partial spawning stage). During the gametogenic cycle, GOI varied significantly in males and in females. Most oocytes were ripe and ready to spawn when their diameter reached or exceeded 45?µm. The expansion of gonad was inversely proportional to the development of the foot tissue. Glycogen concentration showed significant temporal variations between tissues, indicating the clear differentiation in energy storage between the clam organs.     

Reproductive cycles in a reared strain of the mummichog, a daily spawner

Annual, lunar, and diel samplings were taken from a strain of mummichog (Arasaki strain) reared in outdoor tanks under natural conditions, to examine gonadal maturity. Gonads of yearling fish were quite immature in September. During late autumn and winter, a gradual increase in the GSI of both sexes was observed, and the growth of cortical alveolus phase oocytes in females and basal spermatogenesis in males progressed. In late February, a rapid increase in the GSI of both sexes, vitellogenesis in females, and active spermatogenesis in males, occurred. The spawning period of the yearling fish was from late March to August judging from the presence of milt-producing males and ovulated females. The spawning period of the underyearling fish started in the same month as the yearlings, but terminated 1 month earlier. Plasma levels of oestradiol-17 β (E₂) in females and testosterone in males were high during the spawning period in the yearlings. In the underyearlings, however, E₂ levels peaked in early spring, and declined in the latter part of the spawning period. Neither a lunar nor semilunar cycle was evident in the reproductive activity of this fish, which proved to be a typical daily spawner. Females showed an apparent daily reproductive cycle; oocyte maturation commenced at about 1200 hours, germinal vesicle breakdown (GVBD) occurred at about 2400 hours, and ovulation was completed by 2400 hours, 24 h after GVBD. Such clear annual and daily reproductive cycles make this strain of mummichog a suitable model for the study of environmental and endocrine regulation of reproductive cycles in marine and estuarine teleosts.     

Comparative study of sexual cycles, oogenesis and spawning of two Soleidae, Solea lascaris (Risso, 1810) and Solea impar (Bennet, 1831), on the western coast of Brittany

Two sand sole species, Solea lascaris and Solea impar , are common on the western coast of Brittany, France. Their reproduction (oogenesis and spawning) has been studied by following the gonadosomatic index, histological changes in ovary development, and oocyte diameter distribution. Both species have a prolonged spawning season, from spring to late summer. Each mature female breeds twice during the spawning season: in May and July for 5. lascaris , and in early June and July for 5. impar. Throughout the spawning season, several oocyte batches undergo vitellogenesis and there is a continuous recruitment of immature or primary oocytes into vitellogenesis. The two species are thus serial synchronous spawners. This, together with oocyte atresia late in the season (especially noticeable in S. impar ) makes fecundity estimation difficult.     

REPRODUCTION SEXUÉE D'UNE ASTÉRIE FISSIPARE,SCLERASTERIAS RICHARDI (PERRIER, 1882) / SEXUAL REPRODUCTION IN A FISSIPAROUS ASTEROID,SCLERASTERIAS RICHARDI (PERRIER, 1882)

Sclerasterias richardi, a relatively deep sea asteroid (140–200 m) from the border of the Mediterranean continental shelf, is characterized by an asexual reproduction by fissiparity concomitant with a functional sexuality.

A monthly sampling of a population from Calvi (Corsica) has allowed a study of the complete sexual cycle from 354 histologically-treated specimens.

The 218 sexually defined animals (62% males, 38% females) show strict gonochorism. In males, spermatogenesis is cyclic and sexual maturity seems to be reached before that of the females. In females, the different stages of oogenesis are well marked: oogonia and parietal oocytes disappear only at maturity. Oligolecithic oocytes (120–150 μn) show a synchronous growth.

The annual reproductive cycle is well defined in both sexes with one spawning period from mid-September to mid-October.

After spawning, a resting period (from mid-October to mid-January) occurs during which unspawned oocytes are phagocytized by more or less isolated accessory cells. These phagocytic cells have never been found in male specimens.

Each month the presence of specimens without gonads or unsexable individuals is one of the characteristics of this cycle. Their high proportion during the organization stage and after spawning can be easily explained. In March they are frequent too, owing to the infestation of gonads by Ciliates.

As shown by our samples, the bottom water temperature is nearly the same during the whole year and cannot be directly involved as the dominant exogenous variable stimulating spawning.

As a consequence of fissiparity which affects the main part of the population there is a great inter- and intra-individual variability.

The reproductive potentiality is low: as a female emits approximatly 400–500 ova whose development produces planktotrophic larvae with a long pelagic life, it is clear that sexual reproduction is accessory in comparison with asexual reproduction by fission.     

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%).