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.     

Ovarian maturation of Penaeus subtilis (Decapoda: Penaeidae): A new insight to describe oocyte development and somatic structures

We observed the presence of follicular cells (FC) in the ovaries of Penaeus subtilis (n = 1198), which led us to classify the development of germ cells into six phases: oogonia, previtellogenic oocytes, primary and secondary vitellogenic oocytes, mature oocytes and atretic oocytes. The FC changes their shape according to the development of germ cells and showed a different distribution along the ovary, which allowed differentiating vitellogenic oocytes into primary and secondary. We also observed that the postovulatory follicles (POF) are composed of follicular cells. The presence of POF in penaeids ovaries is rarely reported, but allows the differentiation between spent and resting stages, commonly grouped in reproductive biology research. Furthermore, observation of ovarian lining was useful to differentiate immature females from females that had spawned at least once. Thus, ovarian development was classified into six stages: immature, early developing, advanced developing, ripe, spent and resting. The distribution and shape variations of FC, ovarian lining features and presence of POF were considered crucial for the classification of ovarian maturation stages. The methods developed here may improve estimates of their reproductive cycle, size at first maturity and spawning season, which are important variables in future studies of the reproductive dynamics.     

Proliferation of Oogonia and folliculogenesis in the viviparous teleost Ilyodon whitei (Goodeidae)

Oogonial proliferation in fishes is an essential reproductive strategy to generate new ovarian follicles and is the basis for unlimited oogenesis. The reproductive cycle in viviparous teleosts, besides oogenesis, involves development of embryos inside the ovary, that is, intraovarian gestation. Oogonia are located in the germinal epithelium of the ovary. The germinal epithelium is the surface of ovarian lamellae and, therefore, borders the ovarian lumen. However, activity and seasonality of the germinal epithelium have not been described in any viviparous teleost species regarding oogonial proliferation and folliculogenesis. The goal of this study is to identify the histological features of oogonial proliferation and folliculogenesis during the reproductive cycle of the viviparous goodeid Ilyodon whitei. Ovaries during nongestation and early and late gestation were analyzed. Oogonial proliferation and folliculogenesis in I. whitei, where intraovarian gestation follows the maturation and fertilization of oocytes, do not correspond to the late oogenesis, as was observed in oviparous species, but correspond to late gestation. This observation offers an example of ovarian physiology correlated with viviparous reproduction and provides elements for understanding the regulation of the initiation of processes that ultimately result in the origin of the next generation. These processes include oogonia proliferation and development of the next batch of germ cells into the complex process of intraovarian gestation. J. Morphol. 275:1004–1015, 2014. © 2014 Wiley Periodicals, Inc.     

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.     

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.     

Phenological and distributional shifts in ichthyoplankton associated with recent warming in the northeast Pacific Ocean

Understanding changes in the migratory and reproductive phenology of fish stocks in relation to climate change is critical for accurate ecosystem‐based fisheries management. Relocation and changes in timing of reproduction can have dramatic effects upon the success of fish populations and throughout the food web. During anomalously warm conditions (1–4°C above normal) in the northeast Pacific Ocean during 2015–2016, we documented shifts in timing and spawning location of several pelagic fish stocks based on larval fish samples. Total larval concentrations in the northern California Current (NCC) during winter (January–March) 2015 and 2016 were the highest observed since annual collections first occurred in 1998, primarily due to increased abundances of Engraulis mordax (northern anchovy) and Sardinops sagax (Pacific sardine) larvae, which are normally summer spawning species in this region. Sardinops sagax and Merluccius productus (Pacific hake) exhibited an unprecedented early and northward spawning expansion during 2015–16. In addition, spawning duration was greatly increased for E. mordax, as the presence of larvae was observed throughout the majority of 2015–16, indicating prolonged and nearly continuous spawning of adults throughout the warm period. Larvae from all three of these species have never before been collected in the NCC as early in the year. In addition, other southern species were collected in the NCC during this period. This suggests that the spawning phenology and distribution of several ecologically and commercially important fish species dramatically and rapidly changed in response to the warming conditions occurring in 2014–2016, and could be an indication of future conditions under projected climate change. Changes in spawning timing and poleward migration of fish populations due to warmer ocean conditions or global climate change will negatively impact areas that were historically dependent on these fish, and change the food web structure of the areas that the fish move into with unforeseen consequences.     

Control of oocyte recruitment: regulative role of follicle cells through the release of a diffusible factor

To determine whether oogonial proliferation and oocyte recruitment are under control of hypophyseal and/or ovarian factors, we carried out a series of investigations using Podarcis sicula, a lizard inhabiting the temperate lowlands of Europe in which oocyte recruitment occurs throughout the year, as animal model. Germinal beds containing oogonia and oocytes in prefollicular stages were cocultured with different ovarian compartments in presence/absence of FSH, and the effects of different treatments were evaluated by counting the number of prelepto-leptotene oocytes. Results revealed that oocyte recruitment from the pool of oogonia is under the control of a factor released by follicle cells while FSH has an indirect effect on modulating oogonial proliferation. SDS-PAGE analyses carried out on media conditioned by follicles suggest that the factor involved in the control of oocyte recruitment may be a small protein (about 21 kDa) and that its release is dependent on the period of the ovarian cycle but apparently not on the circulating levels of FSH.     

Some aspects of the reproductive biology ofBarbus spp.,Capoeta damascina and their hybrids (Cyprinidae, Teleostei) in Israel

The reproductive biology and gonad cycle of three Cyprinid fish species:Barbus canis (Valenciennes, 1842),B. longiceps (Valenciennes, 1842) andCapoeta damascina (Valenciennes, 1842), in the upper Jordan River system of Israel were studied by monthly sampling over a two-year period. The reproductive activity of the three species was found to peak from January to April, mostly involving upstream migration towards spawning grounds on river beds 400–900 m above the Jordan River. Hybrids of the three species were collected in nature: in those ofBarbus canis ×Capoeta damascina, the gonads possessed both types of gametes, spermatogonia and oogonia, all of which became arrested at an early stage of development, and infertile; in hybrids of detected in nature, males had oocytes dispersed in the testis, whereas in females, the ovaries had small islets of spermatogonial tissue. In these female hybrids the oocytes ripened normally and spawning occurred.     

Responses by four seabird species to a fluctuating availability of Cape Anchovy Engraulis capensis off South Africa

In recent years, Cape Anchovy Engraulis capensis has been the most important food for four seabirds breeding in South Africa–African Penguin Spheniscus demersus, Cape Gannet Morus capensis, Cape Cormorant Phalacrocorax capensis and Swift Tern Sterna bergii. Between 1984 and 1992, biomass of spawning anchovy fluctuated between about 0.5 and 1.75 million tons. Abundance of anchovy was significantly related to numbers of chicks fledged by African Penguins, occurrence of anchovy in the diet of Cape Gannets and numbers of Cape Cormorants and Swift Terns that attempted to breed. Numbers of African Penguins and Cape Gannets that attempted breeding probably also were influenced by abundance of anchovy. African Penguins and Cape Cormorants abandoned nests when anchovy were scarce and deferred breeding until anchovy became more plentiful. Survival of immature African Penguins in a period of anchovy scarcity was enhanced by availability of South African Sardine Sardinops sagax as an alternative food. When anchovy abundance was low, Cape Gannets fed on sardine.     

Microscopic structures of the ovary and female genital ducts of Supachai's caecilian,Ichthyophis supachaii Taylor, 1960 (Amphibia: Gymnophiona)

The structures of the female reproductive system (ovary, oviduct and cloaca) of Ichthyophis supachaii were investigated by dissection, histology and light microscopy. Paired, elongated, sac‐like ovaries are parallel to the gut and fat bodies. Follicle stages include germinal nests of oogonia and primary oocytes, early and late previtellogenic follicles, early and late vitellogenic follicles and atretic follicles. Germinal nests of oogonia comprise oogonia and prefollicular cells. Nests of primary oocytes contain clusters of synchronously developing primary oocytes enclosed by connective tissue. Primary oocytes are associated with follicular cells. Previtellogenic follicles initially form the vitelline envelope, theca cell layers and patches of ooplasmic glycoproteins. Vitellogenic follicles contain heterogeneously sized spherical yolk granules. Atresia is present in several stages of developing follicles. The oviduct is divided into the anterior, middle and posterior parts. All oviductal parts are lined by non‐ciliated epithelium. A small number of mucous cells are present in the middle part. The cloaca of female I. supachaii is divided into the anterior and posterior chambers. The anterior chamber is lined by glandular stratified columnar epithelium, while the posterior chamber has stratified cuboidal epithelium with less mucus production. Our results contribute to useful information on the reproductive biology of caecilians.     

Ovarian structure,folliculogenesis and oogenesis of the annual killifish Millerichthys robustus (Cyprinodontiformes: Cynolebiidae)

Cellular aspects of oocyte development of the Mexican rivulus Millerichthys robustus were morphologically described in order to analyze ovarian function and the cellular recruitment dynamics associating it with life history strategies of annual killifishes. Millerichthys is an iteroparous batch spawner with continuous oocyte recruitment and indeterminate fecundity with asynchronous development of the follicles. It has two ovaries of cystovarian type, with a central lumen, which communicates with the outside through the caudal region of the ovary, that is, the gonoduct. From the walls of the ovary, irregular lamellae composed of germinal epithelium and vascularized stroma project. Oogenesis starts with oogonial proliferation, found alone or in nests within the germinal epithelium. The oogonia come into meiosis becoming oocytes and advancing to the chromatin nucleolus stage and to early primary growth stage. Folliculogenesis is completed in the primary growth stage and cortical alveoli step. Follicles moves toward the stroma, but they continue to be attached to the germinal epithelium through the basement membrane until ovulation. The inclusion of fluid yolk in the follicles during the secondary growth stage was observed. During ovulation, the follicle collapsed, the oocyte was released into the lumen, and the constitutive elements of the post-ovulatory follicle complex remained in the stroma.     

Seasonal histological changes in the gonads of Sebastodes paucispinis ayres,an ovoviviparous teleost (family scorpaenidae)

The elongate paired testes of Sebastodes paucispinis consist of tubules which radiate from a single longitudinal sperm duct and terminate blindly at the periphery of the testis. They are lined by an epithelium consisting of columnar cells with distinct elliptical nuclei. During fall and winter, germ cells migrate inward from the fibrous capsule of the testis and become lodged among the tubule-boundary cells of the seminiferous tubules where they mature into primary spermatogonia. Each of these undergoes several mitotic divisions to produce large cysts of secondary spermatogonia. Subsequent spermatogenic divisions within these cysts produce large sperm-filled cysts which rupture, releasing the spermatozoa into the lumina of the seminiferous tubules. Seasonal cycles of cholesterol and carbohydrate production by the tubule-boundary cells suggest that they perform the same functions as the Leydig cells (androgen production) and Sertoli cells (nutrition) of other vertebrates. The paired fusiform ovaries consist of spongy tissue surrounded by thin-walled muscular ovisacs that converge posteriorly to form a genital duct. The spongy tissue is arranged in transverse lamellae composed of fibrovascular trunks which support epithelial and ovigerous tissue. A series of oocytes (up to 150 μ in diameter) is produced continually from oogonial nests distributed throughout each lamella. Vitellogenesis begins in July and continues throughout the summer. The follicle surrounding the mature oocyte consists of a bilaminar striated vitelline membrane, two epithelial layers (granulosa and theca), and a profuse capillary network. Spermatozoa appear within the ovaries from October to March. Ovulation probably precedes fertilization since spermatozoa were never found within pre-ovulatory or post-ovulatory follicles. The follicular epithelium regresses after ovulation but the capillary beds remain intact, thus providing a mechanism for fetal-maternal exchange of gases and nitrogenous wastes.     

Sexual maturation in female triploid plaice, Pleuronectes platessa, and plaice × flounder, Platichthys flesus, hybrids

The gonads of immature female triploid plaice ( Pleuronectes plafcssa ) and plaice × flounder ( Platichthys flesus ) hybrids produced from cold-shocked eggs were examined. They were less than half the size of those in diploids of similar age and contained only small numbers of developing oocytes. These were similar both in size and cytological appearance to those in the controls. The bulk of the ovarian tissue was composed of nests of small undifferentiated cells resembling the oogonia in the ovaries of diploid fish. Mature, 5 year old triploid hybrids which had not produced eggs over the previous two spawning seasons were killed in January when the diploid controls were nearing spawning condition. The ovaries of these fish were smaller than those of the controls and contained degenerating oocytes at maturation stage V. The advantage of sterile female triploid fish for fish-cultivation is discussed.     

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.     

An overview of cell renewal in the testis throughout the reproductive cycle of a seasonal breeding teleost, the gilthead seabream (Sparus aurata L)

The gilthead seabream is a protandrous hermaphrodite seasonal breeding teleost with a bisexual gonad that offers an interesting model for studying the testicular regression process that occurs in both seasonal testicular involution and sex change. Insofar as fish reproduction is concerned, little is known about cell renewal and elimination during the reproductive cycle of seasonal breeding teleosts with asynchronous spermatogenesis. We have previously described how acidophilic granulocytes infiltrate the testis during postspawning where, surprisingly, they produce interleukin-1beta, a known growth factor for mammalian spermatogonia, rather than being directly involved in the elimination of degenerative germ cells. In this study, we are able to discriminate between spermatogonia stem cells and primary spermatogonia according to their nuclear and cytoplasmic diameters and location in the germinal epithelium, finding that these two cell types, together with Sertoli cells, proliferate throughout the reproductive cycle with a rate that depends on the reproductive stage. Thus, during spermatogenesis the spermatogonia stem cells, the Sertoli cells, and the developing germ cells (primary spermatogonia, A and B spermatogonia, and spermatocytes) in the germinal compartment, and cells with fibroblast-shaped nuclei in the interstitial tissue proliferate. However, during spawning, the testis shows few proliferating cells. During postspawning, the resumption of proliferation, the occurrence of apoptotic spermatogonia, and the phagocytosis of nonshed spermatozoa by Sertoli cells lead to a reorganization of both the germinal compartment and the interstitial tissue. Finally, the proliferation of spermatogonia increases during resting when, unexpectedly, both oogonia and oocytes also proliferate. This proliferative pattern was correlated with the gonadosomatic index, testicular morphology, and testicular and gonad areas, suggesting that complex mechanisms operate in the regulation of gonocyte proliferation in hermaphrodite fish.     

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.     

Reproduction in the piranha Serrasalmus spilopleura, a neotropical fish with an unusual pattern of sexual maturity

Synopsis Reproduction in female Serrasalmus spilopleura (Characiformes, Characidae) from the Itumbiara reservoir (18°28 S, 48°36 W), Paranaíba River, Brazil, was examined with emphasis on the relationship between condition factors and coelomic fat, the annual reproductive cycle and the unusual dynamics of its sexual maturity. The condition factor and coelomic fat index follow a similar pattern along the stages of reproductive cycle. Variations in the condition factor along the reproductive cycle were assigned to variations in the fat contents of the carcass. Serrasalmus spilopleura exhibits characteristics of partial spawning fish and reproduces throughout the year. Sexual maturity occurs at 17.8 cm standard length. Resting and totally spent females were not captured. Females cycle from partially spent to intermediate/advanced maturation without going into the totally spent or resting stages. The initial maturation stage is restricted to fish of intermediate size. Once the initial maturation stage has started the fish remains there for a considerable period of its lifetime before entering in the intermediate maturation stage, an uncommon sexual maturity pattern. The long duration of the initial maturation stage was responsible for the females not returning to the resting stage after spawning.     

Cytophotometric and autoradiographic evidence for functional apomixis in a gynogenetic fish,Poecilia formosa and its related,triploid unisexuals

Summary Amounts of DNA in individual Feulgen-stained nuclei from squash preparations of ovaries and testes from wild-caught and laboratory-reared stocks of Poecilia spp. were determined with an integrating microdensitometer. The DNA content of primary spermatocytes (4C) at zygotene, pachytene, or at metaphase I (3.3–3.4 pg) was approximately twice that found in secondary spermatocytes (2C) and four times that found for young spermatids (1C). Rarely, mature sperm were found with 2C DNA amounts. Nuclei from follicular epithelium and oogonia from both bisexual and diploid unisexual fish contained about 1.6–1.7 pg DNA; whereas, the DNA content of primary oocyte nuclei was about 3.5–3.7 pg DNA, indicating that just one cycle of chromosomal replication had occurred in these cells during the period of DNA synthesis before the visible onset of meiotic prophase. Similar results were obtained for triploid unisexuals whose 6C primary oocyte nuclei contained 5.0–5.1 pg DNA, which was twice the DNA content of 3C oogonia and follicular epithelial cells (2.4–2.5 pg DNA). Autoradiographic studies, designed to monitor the incorporation of ³H-thymidine by oogonia and primary oocytes in vivo and in vitro, also showed that there is no additional synthesis of DNA during the course of meiotic prophase in these unisexual fish. Therefore, we conclude that apomixis, not endoreduplication, is the cytological basis of reproduction in Poecilia formosa and its related, triploid biotypes.     

Involvement of GnRH neuron in the spermatogonial proliferation of the scallop, Patinopecten yessoensiss

The aim of this study was to quantitatively analyze a pattern of proliferation of gonial cells and to demonstrate neural involvement in spermatogonial proliferation of the scallop by the in vitro experiment. Immunocytochemistry for incorporated BrdU was used to identify mitotically active gonial cells. The pattern of proliferation of gonial cells was divided into two phases: phase I; oogonia and spermatogonia slowly proliferate through the growing stage: phase II; oogonia develop into oocytes and spermatogonia start to proliferate rapidly from the mature stage through the spawning stage. The neurons detected with anti-mammalian (m)GnRH antibody were distributed sparsely in the pedal ganglion and predominantly in the cerebral ganglion of both sexes at the growing stage. The extracts from the cerebral and pedal ganglion (CPG) of both sexes collected at the growing stage promoted proliferation of spermatogonia in the in vitro culture of the testicular tissue as well as mGnRH. However, CPG extract had no effect on oogonial proliferation. The increased mitotic activity induced by CPG and mGnRH was abolished by the addition of mGnRH antagonists and anti-mGnRH antibody, suggesting that the spermatogonial proliferation is regulated by GnRH-like peptide in CPG of the scallop. The same mitotic activity as CPG extract and mGnRH was observed in the hemocyte lysate, but not in the serum. These findings suggest that the spermatogonial proliferation at phase II in the scallop may be under the neuroendocrine control by GnRH neuron in CPG.