Tertiary Yolk Stage Research Articles

Growth, sexual transition, and maturation of blacktip grouper Epinephelus fasciatus under long-term artificial rearing: Puberty and its associated physiological and endocrine changes

The blacktip grouper Epinephelus fasciatus is considered a valuable marine fish for aquaculture. This study was conducted to obtain information on its age of puberty, growth performance, gonadal development, sexual transition pattern, and plasma sex steroid levels from juvenile stage to maturity in specimens reared in captivity. The stages of gonadal development were identified by histological analysis, and plasma sex steroid levels were measured using an enzyme-linked immunosorbent assay. Our results show that maturation and spawning in blacktip groupers occurred at almost 3 years of age; although some females matured at 2 years. Plasma 17β-estradiol (E2) levels increased rapidly to high levels during puberty at 3 years of age, especially during the late stage of vitellogenesis at the tertiary yolk stage, and reduced at the ripe and ovulated stages prior to spawning. The gonadal somatic index also showed an increase consistent with the rise in plasma E2 levels. Plasma 11-ketotestosterone (11-KT) levels increased dramatically during sex change and in males. The significant decrease in plasma E2 levels and remarkable increase in plasma 11-KT were the key factors for the progress of sex change in these fish. Interestingly, there were the concomitant appearances of spermatocytes in ovaries of immature females at 1 year 3 months of age. The earliest appearance of sex-transitioning and male fish in blackfish groupers was observed at 2 years, although no mature females were observed below this age. This indicated that the sex change and male transformation in these fish took place without them undergoing the mature female stage. In conclusion, this species had the ability to reach puberty at 2 years of age, but most individuals matured and were functional at 3 years old. Puberty might be affected by age rather than size. In addition, although this species had a protogynous hermaphrodite pattern, when individuals born in the same year were reared together, some individuals were capable of directly becoming males without experiencing a mature female stage. This was due to the lack of socialization in captivity wherein individuals of various ages do not coexist, unlike that in the wild.

Ovarian maturation of Liza ramada in captivity

ABSTRACTIntroduction: Continuous maintenance of broodstock in the captivity and the control of ovarian development are crucial for fish reprodcution, particularly when linked to mass propagation of juveniles in the hatcheries.Aim of the work: The present work was to perform a conclusive description of the maturing ovaries and recruit mature females of thin-lipped grey mullet, Liza ramada suitable for relaiable breeding in captivity.Material and methods: We used the morphological and the histological methods to describe the ovarian cycle of female mullets in captivity. Then, we will use hormonal administration to obtain the mature mullet females in captivity. Results: The ovaries of the fish cultured in freshwater, exhibit marked variation in size, weight and color accompanying the stage of maturity. During ovarian development, only one clutch of oocytes undergoes maturation. Also, six stages of oocyte development could be identified, namely primary oocytes stages, vesicles stage, primary yolk stage, secondary yolk stage, tertiary yolk stage and spawning (ripe) stage. Yolk deposition occurre during vesicles stage, primary yolk stage, secondary yolk stage and tertiary yolk stage. The ovarian development started as early-vitellogenesis when the day length (photoperiod) and water temperature began to decrease. Whereas the gradual decline of both the photoperiod and water temperatures ensure completion of ovary development. However, the ripe stage was absent in captivity, except by hormonal injection. Importantly, the injection of carp hypophyseal homogenate in combination with gonadotropin releasing hormone (triptorelin acetate) was powerful in trigger reproductive activities in mature spawners of mullet.Conclusion: Ripe oocytes are known to be prevailing in the ovaries occur immediately before ovulation. However, ripe oocytes were observed only in the females, acclimated to saline water and stimulated by hormones.

Changes in lipid biology during ovarian development in farmed beluga sturgeon, Huso huso L.

The present study was conducted to understand key biochemical, physiological, and molecular changes associated with ovarian growth and with lipid transfer and/or accumulation into the ovary during oogenesis in captive beluga sturgeon. Plasma levels of triacylglycerides, cholesterol, phospholipid, and sex steroid hormones were determined and all were found to increase notably throughout development from the perinucleolar to the tertiary yolk stage. Using fast protein liquid chromatography, we recognized three major lipoprotein peaks in chromatograms from all samples. These peaks were characterized as containing very low-density lipoprotein (Vldl), low-density lipoprotein/high-density lipoprotein (Ldl/Hdl), and plasma proteins. While Ldl/Hdl represented the most abundant lipoprotein fraction, the relative abundance of different lipoprotein classes did not change with the stage of oogenesis. Eluted lipoproteins were separated using sodium dodecyl-sulfate polyacrylamide gel electrophoresis and sequenced. The peptide sequence spectra for 66-kDa, 205-kDa, 29-kDa, and 70-kDa bands matched with albumin, vitellogenin (Vtg) AB2b, immunoglobulin light-chain precursor, and immunoglobulin heavy-chain, respectively. The large amount of albumin in the plasma protein peak and the confined presence of Vtg AB2b to within Ldl/Hdl reinforce the lipoprotein classification. Lastly, transcript levels of genes encoding ovarian lipoprotein lipase (lpl), apolipoprotein E (apoe), very low-density lipoprotein receptors (vldlr), and low-density lipoprotein receptor-related protein 8-like (lrp8) were estimated using quantitative RT-PCR. The high mRNA levels of lpl, apoe, and lipoprotein receptors vldlr and lrp8 in previtellogenic females suggest that sturgeon oocytes need to be prepared to accept and traffic Vtg and lipids internally, before the start of vitellogenesis.

Effects of hypoxia exposure on apoptosis and expression of membrane steroid receptors, ZIP9, mPRα, and GPER in Atlantic croaker ovaries

Hypoxia exposure causes endocrine disruption in croaker resulting in impairment of ovarian growth and oocyte development, but the effects of hypoxia on non-classical steroid actions in fish ovaries in vivo remain largely unknown. Membrane androgen receptor (ZIP9) enhances apoptosis of cultured Atlantic croaker ovarian follicle cells via upregulation of p53 and Bax, and increased caspase 3 activity through non-classical steroid signaling. Conversely, apoptosis is inhibited in these cells by non-classical steroid mechanisms through membrane progestin receptor alpha (mPRα) and G protein-coupled estrogen receptor (GPER). Apoptosis and the expression of ZIP9, mPRα, and GPER were investigated in ovaries of croakers that had been exposed to normoxia (7.0 mg DO/L) or hypoxia (2.0 mg DO/L) for 6 weeks during their period of gonadal recrudescence. The proportion of tertiary yolk stage oocytes was decreased, and the proportions of atretic and apoptotic ovarian follicles were increased in ovaries from hypoxia-exposed fish compared to controls. Ovarian expression of all three receptors was altered after hypoxia exposure. Expression of mPRα and GPER mRNA and protein levels were decreased after hypoxia exposure, consistent with a decline in anti-apoptosis. In contrast, ZIP9 mRNA and protein levels were upregulated 4-fold in hypoxia-exposed fish compared to normoxic controls. The enhanced apoptosis in ovaries of hypoxia-exposed fish was associated with increased caspase-3/7 activity and elevated expression of the pro-apoptotic genes, Bax and p53. The finding that ZIP9 expression was increased in ovaries of croaker exposed to hypoxia provides in vivo evidence supporting ZIP9's proposed function in mediating ovarian follicle cell apoptosis.

Standardization of plasma vitellogenin level for surveying environmental estrogen pollution using the Japanese common goby Acanthogobius flavimanus.

Field surveys of the impact of environmental estrogen (EE) pollution in aquatic wildlife have been conducted using vitellogenin (VTG) as a biomarker to evaluate the influence of EE. However, a standard baseline of VTG level that can be used to evaluate EE pollution has not been fully determined. To the best of our knowledge, the present study is the first to determine the standard baseline VTG level for evaluating the biological effects of EE pollution using the Japanese common goby (Acanthogobius flavimanus) as the target model fish. Plasma VTG and estradiol-17β (E2 ) levels associated with the reproductive cycle of wild goby inhabiting an unpolluted environment were measured. Mean plasma VTG and E2 levels exhibited similar changes, increasing in the yolk vesicle stage and peaking in the tertiary yolk stage in females. However, plasma VTG and E2 levels showed no significant changes in males, remaining at low levels throughout the reproductive cycle. The highest VTG levels in females and males were 1.6mgml-1 and 124.87ngml-1 , respectively. These results indicate that the baseline level (normal level) in males was approximately 130ngml-1 at most. We concluded that the threshold between normal and abnormal levels with a 10% risk rate was 150ngml-1 in the wild male goby. Plasma VTG levels in males captured from Nagasaki Harbor were higher than the threshold in each reproductive developmental stage, indicating the possibility of EE pollution at this site. The biological standard baseline for VTG established in this study is useful for assessing EE pollution in natural waters.

Effects of Zinc Amino Acid in Walking Catfish (Clarias macrocephalus) Female Broodstock First Sexual Maturation

This study examines the effects of zinc amino acid (ZnAA) to the first sexual maturity stage in female broodstock of the Walking catfish, Clarias macrocephalus. The different ZnAA levels of Control (0 ppm ZnAA), ZnAA1 (100 ppm ZnAA) and ZnAA2 (200 ppm ZnAA) in the diet was applied to the first sexual maturation female catfish (Availa®Zn, Zinpro Corporation, Eden Prairie, MN USA). ZnAA accumulation, broodstock maturation analysis and breeding performance were evaluated. The ZnAA treatment has significant different in serum, meat and ovary ZnAA accumulation. The ZnAA treatment increased the fecundity, gonadosomatic index, egg diameter and development of oocytes at tertiary yolk stage. In comparison, the ZnAA treatment was insignificant in estradiol level. During artificial fertilization, the ZnAA treatment enhanced the fertilization rate and the larval survival rate. During recovery breeding, ZnAA treatment significantly increased the egg production and larval hatching rate. The optimum level to enhance the Clarias macrocephalus female broodstock first sexual maturation is ZnAA1.

Cloning and expression of follistatin gene in half-smooth tongue sole Cynoglossus semilaevis during the reproduction cycle

Follistatin (FST) is a monomeric glycoprotein highly enriched in cysteines and belongs to TGF-β superfamily. FST can suppress the secretion of follicle-stimulating hormone and plays a vital role in the reproduction of vertebrates. We used rapid amplification of cDNA ends technology to clone the FST gene of half-smooth tongue sole, Cynoglossus semilaevis. We characterized its phylogenetic context and expression patterns to elucidate its function in the breeding season. The full-length sequence of FST is 1 455 bp and encodes a protein of 321 amino acids. We investigated the expression pattern of FST in C. semilaevis at different stages of reproduction using reverse transcription-polymerase chain reaction (RTPCR). FST mRNA was expressed in all 13 tissues analyzed, and was expressed at high levels in gonad and at slightly lower levels in gill and brain. During the reproductive cycle of C. semilaevis, the transcript level of FST was the highest in the perinucleolus stage, decreased in the primary yolk stage, slightly increased in the tertiary yolk stage, and then reduced to a minimal level in the atretic follicles stage of the ovary. We concluded that FST suppressed follicle-stimulating hormone, which stimulated oocyte development. However, no significant variation was observed across all stages of testis development, although the expression level in the spermatogenesis stage was relatively low, which may result from the regulation of FST by aromatase.

Oogenesis in Shabout Barbus grypus Heckel , 1843

The female Shabout were collected as samples from Dijla river in Baghdad. The oocyte developmental stages were divided in to nine stages, based on nucleus structure , cellular inclusions and ovarian follicle structure ,they are:-( Oogonia stage , Early Perinucleolar Stage , Advanced Perinucleolar Stage , Cortical Alveoli Stage , Primary Yolk Stage , Secondary Yolk Stage , Tertiary Yolk Stage , Migratory Nucleus Stage , Hydration Stage(

Oogenesis in Shabout Barbus grypus Heckel , 1843

The female Shabout were collected as samples from Dijla river in Baghdad. The oocyte developmental stages were divided in to nine stages, based on nucleus structure , cellular inclusions and ovarian follicle structure ,they are:-( Oogonia stage , Early Perinucleolar Stage , Advanced Perinucleolar Stage , Cortical Alveoli Stage , Primary Yolk Stage , Secondary Yolk Stage , Tertiary Yolk Stage , Migratory Nucleus Stage , Hydration Stage(

Life history of the nonnative convict cichlid Amatitlania nigrofasciata in the Haebaru Reservoir on Okinawa-jima Island, Japan

Life history parameters associated with reproductive biology, age, and growth of the convict cichlid (also known as the zebra cichlid) Amatitlania nigrofasciata, which was introduced into the Haebaru Reservoir on Okinawa-jima Island, were estimated using 437 specimens that ranged from 13.7 to 82.9 mm standard length (SL). Lengths of females at first maturity (SL) and 50% maturity (L50) were estimated to be 32.2 and 37.3 mm SL, respectively. The spawning period continued throughout the year, with a peak spawning cycle from March to May 2006–2007. Observations of postovulatory follicles and tertiary yolk stage oocytes indicate that convict cichlids spawn multiple times within a year. Female cichlids that hatched during the peak spawning seasons matured after October of the same year. Batch fecundity of females (32.2–61.2 mm SL) ranged from 65 to 345 (mean ± SD = 155 ± 63). Opaque zones along the outer margins of otoliths formed annually. The maximum age of male and female cichlids was 3 years. The von Bertalanffy growth formulae (VBGF) were expressed as \( {{\hbox{L}}_{\rm{t}}}{ = 57}{.4}\left( {1 - {e^{ - 0.78\left( {t + 0.91} \right)}}} \right) \) for females and \( {{\hbox{L}}_{\rm{t}}}{ = 69}{.5}\left( {1 - {e^{ - 1.07\left( {t + 0.24} \right)}}} \right) \) for males. Males grew larger than females beginning from the first year. Certain life history characteristics, such as year-round spawning and early maturation, probably contributed to the successful establishment of the convict cichlid, and this species in particular is thought to adapt and become established quickly upon introduction to freshwater systems on Okinawa-jima Island.

Annual and lunar-synchronized ovarian activity in two rabbitfish species in the Chuuk lagoon, Micronesia

This study examined the annual and the lunar cycles of ovarian activity in the forktail rabbitfish Siganus argenteus (Quoy & Gaimard, 1825) and the spiny rabbitfish Siganus spinus (Linnaeus, 1758), which were collected from the Chuuk lagoon, Federated States of Micronesia. Gonadosomatic index (GSI) increased in May and June for S. argenteus. For S. spinus, GSI increased in March, and from July to September. During these periods, the ovaries of these species contained oocytes at the tertiary yolk stage or the maturation stage, suggesting that these months are the reproductive season of the two species. During the reproductive season, weekly collection of the lish according to the lunar phase revealed that high GSI occurred around the last quarter moon for S. argenteus and the new moon for S. spinus. In the ovaries, oocytes developed synchronously, and postovulatory follicles, an indicator of spawning, were observed after the respective moon phase, suggesting that these species are restricted lunar-synchronized spawners. Comparisons of the reproductive activity of the two rabbitfishes in the Chuuk lagoon with that in Okinawa waters revealed that there is a geographic difference in the reproductive activity between habitats. However, the lunar phase for exertion of synchronous gonadal maturation and spawning is common in both regions.

Ovarian development and final oocyte maturation in cultured sevenband grouper Epinephelus septemfasciatus

: The histological changes in the ovary of sevenband grouper Epinephelus septemfasciatus were examined during vitellogenesis and final oocyte maturation. Ovaries contained oocytes at the perinucleolus stage at the start of the experiment in January. Oocytes at the primary yolk stage appeared when the gonadosomatic index (GSI) was slightly on the rise in March. After that, vitellogenesis progressed and ovaries contained oocytes at the tertiary yolk stage in May. The GSI increased drastically at the same time. These results suggest that vitellogenesis in sevenband grouper starts or is already in progress in March and is completed by May, In order to clarify the process of final oocyte maturation, luteinizing hormone-releasing hormone (LHRH) analog (des Gly10, [D-Ala6] LHRH ethylamide) was implanted in fish with oocytes at the tertiary yolk stage. The oocytes developed to the migratory nucleus stage in 18 h and reached the maturation stage in 42 h after implantation. This indicates that final oocyte maturation is completed within 42 h after stimulation of gonadotropin-releasing hormone.

Histological observations of seasonal reproductive and lunar-related spawning cycles in the female honeycomb grouper Epinephelus merra in Okinawan waters

Seasonal reproductive and lunar-related spawning cycles of the female honeycomb grouper Epinephelus merra inhabiting Okinawan waters were examined by histological observation of ovaries. Gonadosomatic index (GSI) increased beginning in May and peaked in June. Histological observations revealed that many oocytes laden with yolk were present in the ovaries from May to August. From September to October, ovaries were occupied by immature oocytes. These results suggest that the reproductive season of E. merra lasts for 4 months from May through August in Okinawan waters. When the fish were collected according to the lunar cycle, GSI increased with the approach of the full moon. Oocytes at various development stages were observed from the first quarter to the full moon. Fresh ovulatory follicles were present in the ovaries around the last quarter moon. These results suggest that E. merra has a lunar spawning cycle and spawns between the full moon and the last quarter moon. Ovarian features of the fish collected around the last quarter moon were different among individuals; some fish had many oocytes at the tertiary yolk stage in the ovaries, while the ovaries of the others were occupied by the oocytes at the peri-nucleolus and the oil droplet stages. This observation suggests that a minor release of eggs occurs in this species before or after a major spawning lunar day. Oocytes at the migratory nucleus and the maturation stages were not observed in any ovarian samples. This may mean that maturation of oocytes is related to the spawning behavior of this species and makes rapid progress in the process of aggregation at the spawning sites.

Relationship between ovarian development and serum levels of gonadal steroid hormones, and induction of oocyte maturation and ovulation in the cultured female Korean spotted sea bass Lateolabrax maculatus (Jeom-nong-eo)

Gonad and blood samples were taken from the cultured female Korean spotted sea bass Lateolabrax maculatus from August to November in 1998 and 1999. Under net cage culture, the female fish did not mature and spawn, but spermiation in males occurred spontaneously in the natural spawning season. Gonadosomatic index (GSI) began to increase in September and reached the highest value (10.1±1.8) in mid November, and then decreased sharply in late November. The cultured fish had been in the tertiary yolk stage oocyte longer then the wild fish. After the breeding period, the cultured fish still had tertiary yolk stage oocytes in mid November. Changes in serum levels of gonadal steroids were correlated with ovarian development. Serum estradiol-17β (E 2) level increased in September, reached their highest levels in October and early November (394.6±75.3 and 380.2±96.6 pg/ml, respectively), and then decreased in mid November and in late November ( P<0.05). Serum 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P) maintained low levels (38.5±5.5-48.8±8.9 pg/ml) and was not significantly changed during the experimental period ( P>0.05). The effects of several hormones on the maturation of follicle-enclosed oocytes were examined in vitro. 17,20β-P and human chorionic gonadotropin (hCG) were found to have high potency to induce maturation. When cultured fish with fully grown oocytes in the ovary were injected with hCG at a dose of 1000 or 2000 IU/kg, all the fish matured and ovulated. However, the number of eggs per fish was not sufficient for mass seedling production. Considering all these results, we could infer that the ovarian oocytes of the cultured female Korean spotted sea bass were not matured and ovulated because of the lack of a gonadotropin surge. Moreover, hCG treatment could induce oocyte maturation and ovulation in the cultured fish.

Reproductive biology of the cardinalfish Apogon lineatus in Tokyo Bay, Japan

SUMMARY: Reproductive biology of Apogon lineatus in Tokyo Bay, Japan was studied by histological examination of the gonads and measurement of the gonadosomatic indices (GSI). The spawning season occurred during July–October, with both males and females attaining sexual maturity by the end of their first year (60.0 mm TL). It was indicated that A. lineatus is a multiple spawner by the presence of postovulatory follicles and primary–secondary yolk in the same ovaries during the spawning season and the asynchronism of the development of spermatogenesis. Batch fecundity ranged from 7983 to 19 316 eggs for fish of 76.0 mm TL to 106.0 mm TL, respectively, and increased linearly with fish total length. Increases in oocyte diameter were not observed after the tertiary yolk stage, which suggested an adaptation to mouthbrooding, thereby efficiently utilizing the male's restricted buccal cavity to maximize the number of eggs mouthbrooded.

Lunar spawning in Siganus canaliculatus

A major spawning of the seagrass rabbitfish Siganus canaliculatus occurred 4 days after the new moon in both May and June 1993, and 7 days after the new moon in 1994. The gonadosomatic index (IG) and serum vitellogenin (VTG) levels fluctuated according to the lunar cycle; IG and VTG levels showed peaks at around the new moon and the waning moon, respectively, suggesting that spawning of this species is synchronized with the lunar cycle. Vitellogenic oocytes appeared on day 2 after the first spawning and were fully mature on day 30. When a greater percentage of the most advanced oocytes attained the tertiary yolk stage, they formed a batch and separated from the adjacent group of smaller pre‐vitellogenic oocytes, indicating that S. canaliculatus is a multiple spawner with an ovary belonging to the group‐synchronous type of oocyte development. Batch fecundity, assessed using batches of oocytes at and after the tertiary yolk stage, ranged from c. 0·52 to 2·56 million eggs. The relationship between batch fecundity (F) and fork length (1) can be represented as F=0·0536854L5·07292.

Lunar spawning in Siganus canaliculatus

A major spawning of the seagrass rabbitfish Siganus canaliculatus occurred 4 days after the new moon in both May and June 1993, and 7 days after the new moon in 1994. The gonadosomatic index (IG) and serum vitellogenin (VTG) levels fluctuated according to the lunar cycle; IG and VTG levels showed peaks at around the new moon and the waning moon, respectively, suggesting that spawning of this species is synchronized with the lunar cycle. Vitellogenic oocytes appeared on day 2 after the first spawning and were fully mature on day 30. When a greater percentage of the most advanced oocytes attained the tertiary yolk stage, they formed a batch and separated from the adjacent group of smaller pre-vitellogenic oocytes, indicating that S. canaliculatus is a multiple spawner with an ovary belonging to the group-synchronous type of oocyte development. Batch fecundity, assessed using batches of oocytes at and after the tertiary yolk stage, ranged from c. 0·52 to 2·56 million eggs. The relationship between batch fecundity (F) and fork length (1) can be represented as F=0·0536854L5·07292.

Blood steroid levels in the goldfish: Measurement of six ovarian steroids in small volumes of serum by reverse-phase high-performance liquid chromatography and radioimmunoassay

A reliable and rapid technique for the measurement of estradiol-17β, testosterone, progesterone, 17α-hydroxyprogesterone, 17α,20β-dihydroxy-4-pregnen-3-one, and cortisol by reverse-phase high-performance liquid chromatography and radioimmunoassay in single female goldfish serum samples of 50 μl was developed. The steroids were extracted with Sep-Pak C18 cartridges after heat treatment. While estradiol-17β was assayed directly after extraction, the other steroids were separated on a μBondapak C18 stainless-steel column with acetonitrile:water (53:47, v/v) in 17 min under isocratic conditions, and then quantitated by specific radioimmunoassays. The technique was validated and was shown to be highly accurate, precise, sensitive, and specific for measuring those particular ovarian steroids in goldfish serum. The steroid levels measured in this way were not significantly different from those measured after separation on a Nova-Pak C18 column with methanol:water (56:44, v/v), where all the individual steroids could be completely resolved during a 40-min run. With this technique, the steroid levels in the serum of the goldfish during the secondary yolk stage, the tertiary yolk stage, and at 0 hr after ovulation were determined. While estradiol-17β was found to be significantly higher in the tertiary yolk stage, testosterone was significantly higher in the secondary yolk stage than in the other two stages. There was no significant difference in the levels of cortisol, 17α-hydroxyprogesterone, 17α,20β-dihydroxy-4-pregnen-3-one, and progesterone among the three stages. We conclude that the technique is particularly useful for assaying multiple steroids in very small volumes of biological fluids.

Induced ovulation of the goldfish by oral administration of salmon pituitary extract

Salmon pituitary extract (PEX) or phosphate buffer was orally administered (i.e. intubated) to female goldfish twice at a 24-h interval. The fish were kept at 14°C without spawning substrate. Five out of nine PEX-treated fish ovulated between 27 and 33 h after the first administration. The PEX-treated fish that failed to ovulate possessed oocytes at germinal vesicle breakdown (GVBD) when sacrificed 36 h after the start of treatment. In contrast, none of the nine control fish ovulated. All of the control fish possessed tertiary yolk stage oocytes when the experiment was terminated. Salmon gonadotropin (GtH) levels were quantified from plasma samples of PEX-treated fish by radioimmunoassay. Plasma salmon GtH levels increased markedly after oral administration while goldfish GtH showed only a slight increase. The results indicate that GVBD and ovulation were induced by orally administered salmon GtH. Biological activity of the salmon GtH was conserved even after being incorporated into the circulatory system via the digestive tract.

In vitro estradiol-17β and testosterone production by ovarian follicles of the goldfish, Carassius auratus

In vitro production of estradiol-17β and testosterone by ovarian follicles of goldfish ( Carassius auratus) at different developmental stages in response to human chorionic gonadotropin (HCG) was examined using 18-hr incubations. The vitellogenic follicles (primary and secondary yolk stage) produced estradiol-17β in response to HCG; follicles at the secondary yolk stage produced about five times more estradiol-17β than the primary yolk stage follicles. However, tertiary yolk stage follicles, which could be induced to mature in vitro by HCG treatment, did not produce estradiol-17β. HCG also stimulated testosterone production by follicles at all stages of development; maximal production was observed in tertiary yolk stage follicles. An indirect assessment of aromatase activity at each stage was made. Vitellogenic follicles (primary and secondary yolk stage) produced estradiol-17β when incubated with testosterone, the larger follicles producing about three times more estradiol-17β. Only low levels of estradiol-17β were produced by tertiary yolk stage follicles. Addition of HCG to primary yolk stage follicles slightly but significantly enhanced estradiol-17β production; however, no enhancement was seen with secondary and tertiary stage follicles. These results suggest that the decrease in estradiol-17β production in tertiary yolk stage follicles may be partly due to a decrease of aromatase activity at this stage.