Ripe Oocytes Research Articles

Immunocytochemical and histological studies on the hypophyseal‐gonadal system in the freshwater Nile Tilapia, Oreochromis niloticus (L.), during sexual maturation and spawning in different habitats

The activities of the hypophyseal-gonadal system of O. niloticus in different habitats were investigated using immunocytochemical and histological techniques. The observed physico-chemical results indicated that Lake Nasser water characteristics are within the allowed and desired safety baseline levels. In contrast, Lake Manzalah exhibited high levels of Ca2+, Mg2+, SO42– and heavy metals (Zn, Pb, and Cd). These water conditions affected the activity of the hypophyseal-gonadal axis of tilapia. The secretory and the synthetic activities of GTH and SL cells in the pituitary gland, in general, underwent obvious normal changes during gonad maturation and spawning of O. niloticus in Lake Nasser. In Lake Manzalah, the secretory activity of GTH and SL cells declined. This may be due to the effect of the high levels of heavy metals which interfere with the release of hormones and disturb the feedback mechanisms. In addition, the activity of both PRL and GH cells in Lake Nasser was higher than that of Lake Manzalah, but the synthetic activity of the ACTH and MSH cells was higher in Lake Manzalah. This may be related to the increased stress on fishes and the dark polluted water in Lake Manzalah. Both the environmental and the endocrine impacts in Lake Manzalah caused a decline in the gonadal activity as reflected by the decrease of sperm amount in the ripe testis, the appearance of oocytes in the testis and the degeneration of ripe oocytes (atresia) during the spawning season. J. Exp. Zool. 284:343–354, 1999. © 1999 Wiley-Liss, Inc.

Reproductive biology of the icefish Champsocephalus esox (Günther, 1861) (Channichthyidae)

Champsocephalus esox is the only icefish species found outside Antarctica. In a population from the Beagle Channel, the complete annual reproductive cycle has been determined. Gonad maturity stages have been established for males and females by histological analysis. Males are sexually mature from January–September with a maximum gonadosomatic index (GSI) of 3.63%. Histologically, testes are very homogeneous and the degree of maturation of the testicular cysts is similar among different tubules at the same maturation stage. Running ripe testes have mature sperm and a few spermatogoniae arranged near the blind end of the tubules. In sexually active females that are found from February–November, ovaries contain only ripe oocytes or postovulatory follicles, together with a batch of previtellogenic oocytes. During hydration, oocyte diameter reaches 2.7 mm, and oocyte dry weight increases due to material intake, the maximum GSI in ovulated ovaries is 21.89 and hepatosomatic index (HSI) decreases. These facts suggest a transfer of matter from liver to the gonads. Absolute fecundity ranges from 3303–8600 oocytes. Relative fecundity ranges from 22.5–43.5 oocytes per gram total weight. In C. esox, relative fecundity has a similar range to those quoted for the different C. gunnari populations, whilst mature oocyte diameter is small and reproductive season extended compared to the same parameters in other Channichthyidae.

Gametogenesis and reproductive cycle of the rock shell,Reishia (Thais) clavigera(Neogastropoda: Muricidae), on the west coast of Korea

Gonadal development, gametogenesis, reproductive cycle, and first sexual maturity of Reishia clavigera were investigated monthly from July 1998 to June 1999 through cytological and histological observations. R. clavigera had separate sexes, and was an internal fertilizer. The male penis was located near the two tentacles. The ovary and testis were composed of a great number of oogenic lobules and spermatogenic tubules, respectively. The size of ripe oocyte ranged from 130 to 140 pm in diameter. The peripheral cytoplasm of the germinal vesicle of the ripe oocyte in many cases were surrounded by smaller yolk granules, while the eccentric cytoplasm was occupied with larger ones. The reproductive cycle of R. clavigera could be classified into five successive stages: early active, late active, ripe, spawning, and recovery. Spawning of females occurred from early July to August when the seawater reached above 24.8°C. Spawning of males occurred from early June to August in the water above 22.8°C. Minimum size for sexual maturity of both sexes was above 10.0 mm in shell height. Each egg capsule was a cylinder or spindle in shape, 4–6 mm in length and 1–2 mm in width. Colors of newly spawned egg capsules showed yellowish white or pale yellow, while those with veliger larvae showed pale black, and released larvae or dead egg capsules showed black violet. The fecundity in an egg capsule ranged from 70 to 91 eggs (mean=80.28 eggs).

Phylogenetic significance of the structure of adult ovary and oogenesis in a primitive chilognathan diplopod, Hyleoglomeris japonica Verhoeff (Glomerida, Diplopoda).

Some histological details of the adult ovary of Hyleoglomeris japonica are described for the first time in the glomerid diplopods. The ovary is a single, long sac-like organ extending from the 4th to the 12th body segment along the median body axis, lying between the alimentary canal and the ventral nerve cord. The ovarian wall consists of a layer of thin ovarian epithelium which surrounds a wide ovarian lumen. A pair of longitudinal "germ zones," including female germ cells, runs in the lateral ovarian wall. Each germ zone consists of two types of oogenetic areas: 1) 8-12 narrow patch-shaped areas for oogonial proliferation, arranged metamerically in a row along each of the dorsal and ventral peripheries, and 2) the remaining wide area for oocyte growth. Oogonial proliferation areas include oogonia, very early previtellogenic oocytes, and young somatic interstitial cells, among the ovarian epithelial cells. The larger early previtellogenic oocytes in the oogonial proliferation areas are located nearer to the oocyte growth area, and migrate to the oocyte growth area. They are surrounded by a layer of follicle cells and are connected with the ovarian epithelium of the oocyte growth area by a portion of their follicles. They grow into the ovarian lumen, but their follicles are still connected with the oocyte growth area. Various sizes of the previtellogenic and vitellogenic oocytes in the ovarian lumen are connected with the oocyte growth area; the smaller oocytes are connected nearer to the dorsal and ventral oogonial proliferation areas, while the larger ones are connected nearer to the longitudinal middle line of the oocyte growth area. Following the completion of vitellogenesis and egg membrane formation in the largest primary oocytes, the germinal vesicles break down. Ripe oocytes are released from their follicles directly into the ovarian lumen to be transported into the oviducts. Ovarian structure and oogenesis of H. japonica are very similar to those of other chilognathan diplopods. At the same time, however, some characteristic features of the ovary of H. japonica are helpful for understanding the structure and evolution of the diplopod ovaries. Some aspects of the phylogenetic significance in the paired germ zones of H. japonica are discussed. J. Morphol 231:277-285, 1997. © 1997 Wiley-Liss, Inc.

The reproductive biology of the cyprinid, Thynnichthys thynnoides (Bleeker), in the Chenderoh Reservoir ? a small tropical reservoir in Malaysia

The reproductive biology and breeding cycle of a tropical cyprinid, Thynnichthys thynnoides (Bleeker), from Chenderoh Reservoir, Malaysia was studied from June 1991 to November 1992. A total of 329 and 246 mature females and males and 167 immature females were sampled during the study. Three breeding cycles were observed and the cycles coincided with high reservoir water level which resulted in the floodings of the littoral zone. Five and four gonad developmental stages were observed for females and males, respectively. Oocyte diameter distribution study indicated the species was a total spawner although clutches of ripe oocytes might be released over an extended time period. Fecundity was related to body weight and both absolute and relative fecundity increased with body size. Absolute fecundity ranged from 26962 ± 1484 to 173520 ± 127420 eggs fish−1, whereas relative fecundity ranged from 121 ± 53 to 451 ± 259 eggs g−1 body weight, respectively.

Insulin but not progesterone promotes the biosynthesis of glycogen in Xenopus laevis oocytes: implications on the control of glycogen synthase by phosphorylation, dephosphorylation.

Insulin, the well-known hypoglycemic hormone, mimics progesterone in promoting the resumption of meiosis within the oocyte of Xenopus laevis. Both hormones exert their action through the inhibition of protein kinases and the activation of protein phosphatases. Because glycogen synthase is an enzyme regulated by a kinases/phosphatases cascade, we investigated the effect of insulin and progesterone on the regulation of glycogen synthesis and glycogen synthase throughout the oogenesis of Xenopus laevis oocytes. In this framework the maximal activity of synthase "a" is concomitant with the vitellogenic period characterized by a drastic increase in the amount of glycogen. Oocyte glycogen synthase is inhibited by cAMP-dependent phosphorylation and stimulated by 20 mM Mg2+. The magnesium effect is inhibited by mu molar concentrations of okadaic acid and suggests that oocyte glycogen synthase is activated by dephosphorylation achieved by protein phosphatase-1. The okadaic acid effect is itself thwarted by the specific inhibitor of protein kinase A, confirming the role of this kinase in the regulation of glycogen synthase. Finally, working on intact ripe oocytes, we showed that insulin but not progesterone increases glycogen synthesis and glycogen synthase "a" activity and lowers the rates of phosphorylation, especially in the glycogen-bound proteins.

Annual reproductive cycle of the Japanese holothurian Eupentacta chronhjelmi

The reproductive cycle of the small temperate dendrochirote holothurian Eupentacta chronhjelmi was studied in the intertidal zone of Aoshima Island, in the Seto Inland Sea of Japan, from July 1989 to January 1991. Reproductive status was assessed by the gonadal index method and histological analysis of the largest (tertiary) gonadal tubules. The primary and secondary tubules are cryptic and difficult to find, so no reference to the animal's annual cycle in terms of gametogenesis is made. The gonad wall was thickest in September for females and October for males, when the gonadal index was at its peak the rapid final stages of vitellogenesis in females (and completion of spermatogenesis in males) depleted reserves in the gonad wall, producing gametes that were spawned in October to December. When gametes were spawned in December the gonadal index and gonad wall thickness decreased. We suggest that the gonadal index reflects gonadal growth by oocyte production and an increase in gonad wall thickness. In the laboratory, spawning occurred from midnight to 04:00, at ambient seawater temperature (12 °C). Individuals elevated their anterior, oral end, waved their tentacles, and released gametes for about an hour. Based on its large egg size (300 ± 5 μm (mean ± SE) diameter) and low fecundity (1500 ± 10 ripe oocytes per individual), we infer lecithotropic development with an abbreviated larval stage.

Distribution and reproductive biology of the blackchin guitarfish, Rhinobatos cemiculus (Pisces: Rhinobatidae), in Tunisian waters (central Mediterranean)

Aspects of the reproductive biology of Rhinobatos cemiculus are described from specimens collected in Tunisian waters. Sizes at first sexual maturity of males and females are 1000 mm and 1100 mm total length (TL), respectively. Adult females are generally larger than adult males, the maximum TL for males and females being 1920 mm and 2300 mm, respectively. The smallest gravid female observed was 1220 mm TL. R. cemiculus is an aplacental viviparous species, with each female having two ovaries and two uteri, both functional. Ripe oocytes in the ovaries, ova, embryos and fully developed fetuses in the uteri are symmetrically distributed. The gestation period could last for a maximum of eight months. Vitellogenesis proceeds in parallel with gestation, and at the time of parturition a crop of ripe oocytes is ready to be ovulated. Ovulation and parturition occur during winter and summer, respectively. There is probably one litter per year. The mean TL and mean weight of fully developed fetuses are 39.6 mm and 115.1 g, respectively. A computed chemical balance of development, based on the mean dry weights of fully developed fetuses and ripe oocytes, is 1.01. This low value is due to the fact that R. cemiculus is purely a lecithotrophic species. Fecundity ranges from 5 to 12 young per litter. Ovarian fecundity and uterine fecundity are slightly correlated with the size of females. Females are more numerous than males in the total sample, as well as in utero and at the juvenile stage; however, this is not the case for subadults and adults. This phenomenon is probably due to segregation of the sexes at different depths during certain stages of the reproductive cycle rather than to a high rate of mortality among subadult and adult females.

The biology of the Red Sea migrant, Saurida undosquamis in the Mediterranean and comparison with the indigenous confamilial Synodus saurus (Teleostei: Synodontidae)

A study of the biology of Red Sea — Suez Canal migrant, the lizardfish Saurida undosquamis and the indigenous Synodus saurus was carried out in the Mediterranean coast of Israel. The spawning season of S. undosquamis lasts from March to December indicating a curtailment of the year-round spawning season of the source population in the Gulf of Oman. The spawning season of S. saurus is from February to August. The diameter of ripe oocytes of S. undosquamis is 500–600 µm. Females of S. undosquamis grow slightly faster than males and reach a larger size (340 mm TL versus 280 mm TL). Niche partitioning between the two lizardfishes is primarily on the basis of depth. The invador occupying deeper water. Both species are chiefly piscivorous but as a result of their depth distribution there is little diet overlap on the specific level.

Lunar synchronization of spawning in sea bass, Lates calcarifer (Bloch): effect of luteinizing hormone‐releasing hormone analogue (LHRHa) treatment

Based on egg collection records, spontaneous spawning activity of sea bass, Lates calcarifer (Bloch), reared in floating net cages followed a semilunar cycle. The peak of multiple spawnings coincided with declining spring tides of quarter moon periods. Maximum diameter of intra‐ovarian, ripe oocytes (0.51–0.55 mm) occurred in synchrony with the quarter moon periods. Smaller oocytes (0.44–0.47 mm) were sampled during the new and full moon periods. Two structural analogues of luteinizing hormone‐releasing hormone (LHRHa) (des‐Gly10, d‐Ala6‐LHRH ethylamide and d‐Ala6, Pro9‐Nethylamide‐LHRH), in pelleted or dissolved form, induced mature female sea bass with a mean egg diameter of at least 0.40 mm to spawn at any day during the lunar cycle. The onset of spontaneous and LHRHa‐induced spawnings occurred during low tides in the evening until dawn (from 19.00 to 05.00 hours). These results demonstrate that LHRHa can effectively induce mature sea bass to spawn independent of the highly predictable semilunar spawning rhythm. In addition, the occurrence of both spontaneous and hormone‐induced spawnings at a precise period of the day suggest a tidal and diurnal cue entraining spawning of mature female sea bass.

Biology of Chrysomya megacephala (Diptera: Calliphoridae) and reduction of losses caused to the salted-dried fish industry in south-east Asia

AbstractChrysomya megacephala (Fabricius) is shown to be a principal cause of loss of salted-dried fish in south-east Asia. Field and laboratory work conducted in 1982–1989 was aimed at reducing these losses. Field work at a small–scale fish processing site in Cirebon, West Java, showed that fully gravid C. megacephala females were highly differentially attracted to fish at the salting stage, which means that the salting tanks must have properly designed fly-tight lids to prevent infestation. C. megacephala counts and ovary examinations showed that females with various stages of immature ovaries (stages I–IV) were predominent during the drying stage after the fish had been removed from the salting tanks, with numbers usually greater on the first day of drying than the second. C. megacephala counts were high during the dry season, although numbers fluctuated enormously depending on weather, among other factors. Physically screening fish during the initial drying period effectively controlled infestation, although problems associated with the screen design were identified. In laboratory cultures adult sex ratio was approximately 1:1 and longevity in both sexes, over three generations, ranged from 47 to 55 days (maximum induced longevity, 98 days) at c. 29°C, 30–60% r.h.; under similar conditions, 10% of females had mature (stage V/VI) oocytes after one week, 40% after two weeks and 90% after three weeks. Mean number of ripe oocytes in gravid flies was 221 (range 151–228).

The biology of the Indo‐Pacific squirrelfish, Sargocentron rubrum (Forsskål), a Suez Canal migrant to the eastern Mediterranean

A biological study of the adult population of the Suez Canal migrant, the squirrelfish, Sargocentron rubrum, in the Mediterranean coast of Israel, was carried out between October 1979 and October 1980. Sargocentron rubrum in the Mediterranean has a short spawning season lasting from July to August. The estimated fecundity varied from 108 000 to 646 000 oocytes per mature female. The largest ripe oocytes reach a diameter of 200 μm. The ratio of males to females was found to be 1:2. Hyaline rings on otoliths were used for aging. Growth rate was obtained by back calculation and by using von Bertalanffy's equation. The results obtained from both methods were close, 94mm S.L. after 16 months, 125–127 mm after 28 months, 143 144mm after 40 months and 155 mm after 52 months. Age groups older than 4 years were not found in the present study. The descriptions of early stages of development were based on samples collected by dip and neuston nets along the Mediterranean coast of Israel.

Fertilization in a Crab. III. Cytodifferentiation of vesicles enclosing ring‐shaped elements involved in the cortical reaction

AbstractDuring the cortical reaction, Carcinus maenas eggs successively released a fine granular material and a massive amount of ring‐shaped elements that subsequently formed most of the fertilization envelope. The ring‐shaped elements came from egg cortical vesicles and, owing to their striking morphology, acted as naturally occurring markers in ultrathin sections, which permitted us to understand the pathway of their intracellular transport. In this respect it was established that the ring‐shaped elements and their enclosing vesicles originated in the endoplasmic reticulum both in ripe oocytes and early fertilized eggs maintained under in vitro conditions. The intracellular transport pathway of the endoplasmic reticulum‐derived vesicles seemed to bypass the Golgi apparatus. Accordingly, the ring‐shaped elements appeared to be released by direct exocytosis from the endoplasmic reticulum system.Finally, a tentative scheme of oocytes functioning is suggested for crustacean decapods, based on the remarkable similarities between the structure and ER origin of the ring‐shaped elements involved in the cortical reaction and the disc‐shaped granules traditionally considered as endogenous yolk precursors. The scheme implies that the oocyte ER system might produce a precursor common to the cortical reaction exudate and to the endogenous yolk, in the form of the ring‐ or disc‐shaped elements.

Reproductive biology of the tropical fish Trichogaster pectoralis (Regan)

The breeding cycle of an air‐breathing Anabantid, Trichogaster pectoralis was studied in Malaysia. The species was found to breed all the year but with pronounced peaks of activity associated with the two wetter periods in the year. The advantages of this timing and the cues which stimulate gonadal activity are discussed. From the study of oocyte distribution in selected ovaries it was concluded that T. pectoralis is a total spawner although a batch of ripe oocytes may be released over an extended period of time. Fecundity was found to be related to length of fish by the formula (log10 Egg no.)=–4.6854+4.3080 log10 standard length (S.L.) (mm).

Sex differentiation in bilaterally allophenic animals produced by cloning of two bipartite male/female chimaeras of Lineus sanguineus

Two bipartite chimaeras were constructed in Lineus sanguineus by grafting the lateral halves from a phenotypically dark-brown male onto the anatomically complementary halves from a phenotypically light-brown female. Regeneration of a large number of pieces transected from these two bilaterally allogeneic chimaeras produced two clones of bilaterally allophenic nemertines (male/female and female/male). Sex differentiation in the cloned worms started with a transitory stage of gonad developmental autonomy, termed the primary gynandromorphous state; at this stage there were young testes in the originally male lateral halves and juvenile ovaries in the originally female ones, the only abnormality then was that the ovarian development was more advanced than the testicular development relative to those in male and female controls. Then, unilateral sex reversal occurred, with feminization of the testes, i.e. oogenesis took the place of spermatogenesis in the many male gonads located in either the right or the left side of allophenic worms according to the symmetry patterns of the two clones. Finally, when the gonads reached maturity, both sides allophenic L. sanguineus contained only ovaries with ripe oocytes. The complete feminization of these allophenic worms and the previously observed masculinization of 'heterosexual' chimaeras in L. ruber suggest that a diffusible factor controls gonadal differentiation in worms of the prevailing sex, which is the female sex in L. sanguineus and the male sex in L. ruber.

The activation of gamete migration, maturation and spawning inPectinaria gouldii

A substance obtained from extracts of the subesophageal ganglion and cement gland complex of Pectinaria gouldii will activate the admission of only fully developed coelomic oocytes into the nephromixia, where they exhibit cell surface changes, undergo germinal vesicle breakdown, initiate meiosis and culminate in spawning as ripe oocytes. In the male, similar extracts cause packets of spermatozoa to move into the reproductive chamber, break apart and spawn as free sperm. The stimulus of activation is reciprocal between the sexes. Extracts of the cerebral ganglia are equally effective in males, but the active factor from this tissue is greatly reduced or absent in females. Properties of the active factor are defined. Maturation effectors for starfish oocytes were also tested.

Oogenesis in a tropical loachLepidocephalus thermalis (Cuv. & Val.)

The development of oocytes has been traced in detail in the loachLepidocephalus thermalis. The various stages of oocytes are described under distinctive stages namely 1. chromatin nucleolus stage; 2. perinucleolus stage; 3. yolk vesicle stage; 4. primary yolk stage; 5. secondary yolk stage; 6. tertiary yolk stage; 7. migratory nucleus stage; 8. pre-ripening stage; 9. ripe egg stage. The yolk deposition is initiated as minute globules in the extravesicular ooplasm. A yolk nuclous is entirely wanting in any stage of oocyte maturation. The origin of new crops of oocytes and the formation of the micropyle are described. Nature of degeneration of unextruded ripe oocytes has been followed.

Studies on the reproduction of cirripedes. I. Introduction: Copulation, release of oocytes, and formation of the egg lamellae

A brief outline is given of the sequence of events leading to the production of egg lamellae in operculate and pedunculate cirripedes. Details are given of the copulatory act as regards random and possibly directed movements of the penis; the question of mutual ‘recognition’ is discussed. The time spent by a spermatozoon in the penis is estimated. The release of ripe oocytes is described and the results of some experiments suggesting the presence of an agent suppressing their release in the earlier stage of maturation are given. It is shown that seminal plasma can induce muscle contractions and the possible significance of this is discussed. The behaviour subsequent to copulation is described. Fully motile spermatozoa are found in the mantle cavity and may be expelled in the mantle cavity current. The bulk of the semen sets to a translucent jelly which is eventually lost from the mantle cavity. The formation of this gel is due to general autolysis. The production, properties, and functions of the egg membranes and the oviducal sac are discussed.

A population study of the polychaete Capitella capitata at plymouth

A population of Capitella capitata (Fabricius) was sampled from January, 1973 to February, 1974. Size of the worms was measured and sexual maturity determined. There is an extensive breeding season, spawning occurring asynchronously throughout the year. Females containing ripe oocytes were almost always present, but most females at any one time contained immature oocytes. A high percentage of males contained active sperm. Oocytes are not released into the coelomic fluid until almost fully developed, and all are released at a single spawning. A large number of eggs are produced at each spawning and there is some evidence to suggest that larval development may be completely benthonic. Gametes first develop in 7 to 8 month old worms and take about 4 months to complete development. Analyses of the female population structure suggests that there are 3 breeding classes. The growth rate is estimated at 30 mm per year, and few worms are believed to survive longer than 2 years.

Control of vitellogenesis and of growth of female accessory sex organs by the dorsal body hormone (DBH) in the hermaphroditic freshwater snail Lymnaea stagnalis

A study has been made of the role of the dorsal bodies (DB) and the adjacent neurosecretory light green cells (LGC) of the cerebral ganglia in reproductive activity of the hermaphroditic pulmonate snail Lymnaea stagnalis. The experiment included one series of juvenile snails and one of adult snails. Each series included the following groups: controls, sham-operated controls, and snails with cauterized DB, LGC, or DB+LGC. Implantations were carried out on some of the operated snails on postoperative Day 60. The final observations on all animals were performed on Day 90. Removal of the DB in juvenile as well as in adult snails resulted in a complete absence of ovipository activity. Removal of the LGC resulted only in a temporary decrease of ovipository activity. Ninety Days after the DB were removed from juvenile snails, the percentages of vitellogenic and degenerating oocytes in the ovotestes had decreased, whereas the percentage of previtellogenic oocytes had increased. This indicates that in the absence of the DB the production of previtellogenic oocytes continues, but that vitellogenesis ceases. Reimplantation of the DB restored the normal proportional frequencies and was followed by the onset of ovipository activity within 30 days. Removal of the DB from adult snails had no effect on the proportional frequencies of the female cell types, and also did not result in degeneration of the developing and ripe oocytes. Subsequent reimplantation of the DB was followed by the restart of oviposition. Cauterization and subsequent implantation of the LGC in juvenile and adult snails had no effect on the proportional frequencies of the various types of female cells. Growth of the female accessory sex organs is entirely dependent on the presence of the DB. Again, this was most clearly demonstrated by extirpation and implantation of DB in juvenile snails. No clear effects of DB or LGC on spermatogenesis and growth of the male accessory sex organs were found. It is concluded that the DB produce an endocrine factor, the dorsal body hormone (DBH), that stimulates vitellogenesis and growth of the female accessory sex organs. The stimulation of oviposition by the DBH is thought to be due to the stimulation of vitellogenesis. It is suggested that the effect of the DBH on the female organs will be mediated by the ovotestis.