Postovulatory Follicles Research Articles

Reproductive morphophysiology of an iteroparous batch spawner fish: from early follicle development to ovulation.

Batch spawner fishes develop successive clutches of oocytes which allows them to participate in many reproductive cycles during their adult life (iteroparous) and spawn in multiple events within each breeding cycle. Here, ovarian follicular development was morpho-functionally analyzed in females of the iteroparous batch spawner fish Gymnocorymbus ternetzi. To obtain better insights into the reproductive morpho-physiology in batch spawners, the objective of this research was to analyze the dynamics of the follicular development, with its hormonal regulation between two active reproduction events. We found that over 16 days, follicles progressed asynchronously to chromatin nucleolus, Primary and Secondary growth stages of oogenesis with progressive secretion of 17β-estradiol (E2). During the end of secondary growth, the increase in 17α,20β-dihydroxy-4-pregnen-3-one (17,20β-p) was measured relative to the maturation process of the ovarian follicles (e.g., nuclear migration and its rupture during the resumption of meiosis). Interestingly, an additional increase in E2 was observed after fish reproduction, probably related to the recruitment of new batch follicles for secondary growth. We also measured the high values of multiple condition factor post-reproduction measurements, reflecting more energy invested during the pre-reproductive process. We also quantified high concentrations of 17,20β-p, probably related to the recruitment of a new batch of oogonia to meiosis, presumably secreted by post-ovulatory follicles, after fish reproduction. We finally found that fish without exposure to reproductive stimulus developed a regression phase at day 24, characterized by massive follicle atresia, that allow them to recycle energy and constitutive materials of the follicles invested during oogenesis for another reproductive cycle.

Granulosa Cell-Layer Stiffening Prevents Escape of Mural Granulosa Cells from the Post-Ovulatory Follicle.

Ovulation is vital for successful reproduction. Following ovulation, cumulus cells and oocyte are released, while mural granulosa cells (mGCs) remain sequestered within the post-ovulatory follicle to form the corpus luteum. However, the mechanism underlying the confinement of mGCs has been a longstanding mystery. Here, in vitro and in vivo evidence is provided demonstrating that the stiffening of mGC-layer serves as an evolutionarily conserved mechanism that prevents mGCs from escaping the post-ovulatory follicles. The results from spatial transcriptome analysis and experiments reveal that focal adhesion assembly, triggered by the LH (hCG)-cAMP-PKA-CREB signaling cascade, is necessary for mGC-layer stiffening. Disrupting focal adhesion assembly through RNA interference results in stiffening failure, mGC escape, and the subsequent development of an abnormal corpus luteum characterized by decreased cell density or cavities. These findings introduce a novel concept of "mGC-layer stiffening", shedding light on the mechanism that prevents mGC escape from the post-ovulatory follicle.

Histological characteristics of oocyte differentiation in the captive longnose seahorse Hippocampus trimaculatus (Leach, 1814).

This study aimed to explore the reproductive histology and oocyte differentiation of the longnose seahorse Hippocampus trimaculatus (Leach, 1814) in captivity. Five mature healthy females were histologically observed. The reproductive systems of the five specimens exhibited similar morphological characteristics with a pair of saccular creamy white ovaries merging caudally into a single gonoduct. There were two germinal ridges lined with a layer of germinal epithelium (GE). The ovarian maturation of this species was considered asynchronous. The oogenic cells were classified into oogonia and oocytes at several developmental phases based on their size and characteristics. Oogonia were identified among the connective tissue in the middle area of the GE. The stromal compartment contained oocytes that were classified into four distinct phases: the primary growth (PG) phase having two steps (perinucleolar and oil droplets-cortical alveolar steps) and the secondary growth (SG) phase with three oocyte types, including early SG oocytes, late SG oocytes, and fully grown oocytes. The atretic oocytes (AO) were observed in all stages of oogenesis. Postovulatory follicles were also seen among the ovarian connective tissue. The occurrence of postovulatory follicles suggested that the specimens analysed in this study were in the spawning period. This research provides new insights into the identification of the reproductive cycles and morphological characteristics of the ovary of H. trimaculatus.

Gametogenesis and seminatural reproduction of the Amazon twospot astyanax Astyanax bimaculatus (Linnaeus, 1758) cultivated in an enriched environment

Environmental enrichment is used to provide well-being to the animals, such as fish, in captive conditions, mimicking their natural habitat. It may influence fish behavior, physiology, and survival. In terms of reproduction, however, the relationship between environment enrichment and successful reproduction in captivity is still poorly explored in fish species. Aiming to understand any possible benefits of structural enrichment on fish reproduction, 10-days-hatched larvae of the twospot astyanax Astyanax bimaculatus were raised for 18 weeks in tanks with different elements of structural environmental enrichment (PVC pipes, stones, and artificial plants). In the 5th month of life, those animals were hormonally induced to reproduce to assess gamete formation and offspring quality. Animals raised in a sterile-reared environment (non-enriched) showed earlier spawning than the enriched one, presenting significant quantities of Postovulatory follicle complexes (POCs) and cells in atresia in female ovaries, indicating possible reproductive dysfunction or stress, as well as a greater quantity of empty testicular lumen in males, indicating great release of sperm. On the contrary, animals cultivated in enriched environments showed gonads filled with semen in males and vitellogenic oocytes in females. Furthermore, offspring from the sterile-reared group presented significant rates of larval abnormality compared to the enriched group. In conclusion, the results of this study show that environmental enrichment can interfere with the reproduction of fish in captivity, mainly by preventing early maturation of gametes, which can result in low-quality offspring and, consequently, low production of fish species.

Chitosan nanoconjugation of GnRH analogue augments reproductive performance in Clarias magur (Hamilton, 1822)

A breeding trial was conducted to investigate the impact of a chitosan nanoconjugated formulation of Salmon gonadotropin-releasing hormone analogue (ChN-sGnRH-a) on the induced breeding performance of female Clarias magur (magur). A total of 72 magur breeders were divided into six treatment groups: Cn, the Negative Control (injected with bare chitosan nanoparticles); Cp, the Positive Control (injected with Gonopro-FH®, a commercially available inducing hormone, at a dose of 1 mL/kg body weight of fish); T1, injected with ChN-sGnRH-a at a dose of 1 mL/kg; T2, T1 + 10 mg/kg domperidone; T3, injected with ChN-sGnRH-a at a dose of 0.5 mL/kg; T4, T3 + 10 mg/kg domperidone. Blood was collected at 0 (before injection), 6, 12 and 18 h post-injection to determine the serum steroid profile. In the Cp treatment group, the serum steroid levels of testosterone, estradiol, and 17α, 20β-dihydroxy progesterone in the fish, displayed a sharp increase, peaking at the 6-h post-injection, followed by a significant decrease. However, the fish in the T2 and T4 treatment groups exhibited serum steroid peaks at the 12-h post-injection and maintained those levels up to the 18-h post-injection. The reproductive performance, as measured by spawning fecundity, fertilization rate, and hatching rate, was significantly higher in the T2 treatment group (p < 0.05). No significant differences (p > 0.05) were observed between the Cp and T4 treatment groups. Compared to the Cn treatment group, the mRNA expression levels of pituitary follicle stimulating hormone subunit beta and luteinizing hormone subunit beta, as well as ovarian 17β-hydroxysteroid dehydrogenase type 3, were significantly higher in the T2 treatment group, followed by Cp and T4 treatment groups. Fish in the T2 treatment group displayed fewer mature oocytes and numerous post-ovulatory follicles in their ovaries. Additionally, the ovarian histology of fish in the T4 treatment group closely resembled that of the Cp treatment group. The results indicate that the chitosan nanoconjugated formulation of Salmon GnRH analogue might contribute to maintaining elevated levels of gonadotropic and steroid concentrations, resulting in improved reproductive output in female magur breeders. It is also revealed that the induced breeding of magur cannot be achieved without using dopamine inhibitors in GnRH analogue injection. Using chitosan nanoparticles as a nano-delivery system could reduce the Salmon GnRH analogue dose without compromising the reproductive performance of female magur breeders.

Molecular characterization and expression profile of estrogen receptor subtypes in female hilsa (Tenualosa ilisha)

Hilsa (Tenualosa ilisha), a highly prized edible fish, is consumed by over 250 million people worldwide. Estrogens are essential hormones required during reproduction and bind with estrogen receptors in target organs for biological activity. The two unique subtypes of the estrogen receptor found in fish are alpha (α) and beta (β) and exhibit distinctive roles in reproduction. The present study aimed to understand the breeding physiology of hilsa during the seasonal gonadal cycles through GSI seasonal variation, histological study, and molecular identification, characterization, and transcriptional modification of estrogen receptors in hilsa. Monthly GSI analysis from females showed that during September, the GSI value was maximum (22.01 ± 0.68), followed by the May GSI value (18.78 ± 0.97). Histological observation showed the formation of asynchronous gametes during the development of ovaries. The histological analysis revealed the formation of developing oocytes, nucleus, presence of primary oogonia, secondary oogonia, chromatin nucleolar oocytes, and early perinucleolar oocytes in the ovary (January–early July). Progressively, formations of the yolk vesicles, yolk granule stage, premature stage, and mature stage with post-ovulatory follicles were also identified. Linear observation was recorded during the monsoon season from July to November. Furthermore, partial length cDNAs for estrogen receptors were characterized, and their mRNA expression patterns demonstrate that ER-α expression significantly increased in September, followed by April and August in the ovary and liver tissue. Both the liver and ovary showed the highest mRNA expression of ER-β in September. The study revealed that ER-α expression was higher in the ovary as compared with liver tissue. Furthermore, we introduce three-dimensional (3D) models depicting the hilsa estrogen receptors in complex with estradiol (E2), constructed through homology modeling. This investigation contributes valuable insights into the molecular characteristics of estrogen receptors in this teleost fish. Our present work provided preliminary evidence of estrogen receptors during reproduction in hilsa.

Proteo-transcriptomic profiles reveal key regulatory pathways and functions of LDHA in the ovulation of domestic chickens (Gallus gallus)

BackgroundIn poultry, the smooth transition of follicles from the preovulatory-to-postovulatory phase impacts egg production in hens and can benefit the poultry industry. However, the regulatory mechanism underlying follicular ovulation in avians is a complex biological process that remains unclear.ResultsCritical biochemical events involved in ovulation in domestic chickens (Gallus gallus) were evaluated by transcriptomics, proteomics, and in vitro assays. Comparative transcriptome analyses of the largest preovulatory follicle (F1) and postovulatory follicle (POF1) in continuous laying (CL) and intermittent laying (IL) chickens indicated the greatest difference between CL_F1 and IL_F1, with 950 differentially expressed genes (DEGs), and the smallest difference between CL_POF1 and IL_POF1, with 14 DEGs. Additionally, data-independent acquisition proteomics revealed 252 differentially abundant proteins between CL_F1 and IL_F1. Perivitelline membrane synthesis, steroid biosynthesis, lysosomes, and oxidative phosphorylation were identified as pivotal pathways contributing to ovulation regulation. In particular, the regulation of zona pellucida sperm-binding protein 3, plasminogen activator, cathepsin A, and lactate dehydrogenase A (LDHA) was shown to be essential for ovulation. Furthermore, the inhibition of LDHA decreased cell viability and promoted apoptosis of ovarian follicles in vitro.ConclusionsThis study reveals several important biochemical events involved in the process of ovulation, as well as crucial role of LDHA. These findings improve our understanding of ovulation and its regulatory mechanisms in avian species.

Recent Findings on Spawning Patterns and Recommendations for the Fishery Management of the Southern Red Snapper—Lutjanus purpureus (Poey, 1866)—On the Amazon Continental Shelf of Brazil

The southern red snapper, Lutjanus purpureus, is one of the primary fishery resources of the Amazon continental shelf. Due to the demand for specimens of less than 900 g in weight, increased fishing effort focusing on this size class has led to a drastic decrease in catches. The present study was based on the analysis of cellular structures in the female gonads (formation of oocytes and other reproductive tissues) to identify reproductive processes and evaluate the effectiveness of current fishery management practices. The presence of postovulatory follicles (POFs) peaked in April, which was interpreted as a period of intense spawning. In addition to POFs, hydrated oocytes peaked in July, indicating either reproductive continuity or a second peak, based on the presence of atretic oocytes and atresia. Given that the local snapper fishery preferentially targets very young individuals, an extension of the closed season from March to July would be recommendable to guarantee the reproductive potential of the spawning stock.

MiRNA profiling of chicken follicles during follicular development

MicroRNAs (miRNAs) play a crucial role as transcription regulators in various aspects of follicular development, including steroidogenesis, ovulation, apoptosis, and gene regulation in poultry. However, there is a paucity of studies examining the specific impact of miRNAs on ovarian granulosa cells (GCs) across multiple grades in laying hens. Consequently, this study aims to investigate the roles of miRNAs in chicken GCs. By constructing miRNA expression profiles of GCs at 10 different time points, encompassing 4 pre-hierarchical, 5 preovulatory, and 1 postovulatory follicles stage, we identified highly expressed miRNAs involved in GC differentiation (miR-148a-3p, miR-143-3p), apoptosis (let7 family, miR-363-3p, miR-30c-5p, etc.), and autophagy (miR-128-3p, miR-21-5p). Furthermore, we discovered 48 developmentally dynamic miRNAs (DDMs) that target 295 dynamic differentially expressed genes (DDGs) associated with follicular development and selection (such as oocyte meiosis, progesterone-mediated oocyte maturation, Wnt signaling pathway, TGF-β signaling pathway) as well as follicular regression (including autophagy and cellular senescence). These findings contribute to a more comprehensive understanding of the intricate mechanisms underlying follicle recruitment, selection, and degeneration, aiming to enhance poultry’s reproductive capacity.

Aspectos reprodutivos das fêmeas de Leporinus lacustris Campos, 1945 (Characiformes, Anostomidae) em uma planície de inundação Neotropical

Abstract: Aim This study evaluates the reproduction and fecundity of Leporinus lacustris in upper Paraná River floodplain environments with the objectives to (i) recognize the germ cells of folliculogenesis and oogenesis; (ii) characterize reproductive phases; (iii) investigate oocyte diameter and evaluate if this species has group synchronous or asynchronous oocyte development and if spawning is total or batch; (iv) estimate batch fecundity; (v) establish the relationship between fecundity/ovary weight, standard length, and total weight; (vi) verify the reproductive areas of this species in the upper Paraná River floodplain. Methods Sampling was carried out using gillnets in rivers, and open and closed lagoons, in March, June, September, and December 2013, 2014, 2015, 2016, 2018, and 2019 and March and September 2017. A total of 442 females were sampled and 111 subsampled, each of which had an ovary removed and fixed in Bouin solution. A subsample of 20 ovaries in the spawning capable phase were fixed in a 4% buffered formaldehyde solution to estimate the diameter of the oocytes and fecundity. The ovaries were dehydrated, embedded in historesin, cut, stained, and evaluated as regards folliculogenesis, oogenesis, development phases, and reproduction areas. Results The germ cells recorded were differentiated oogonia, primary and secondary growth oocytes, fully-grown and mature oocytes, and post-ovulatory follicles that permitted the recognition of the reproductive phases. Oocyte diameter information revealed that the species has group synchronous oocyte development, determinate fecundity and batch spawning, and eliminates an average of 38,490 oocytes. Conclusions The fact that Leporinus lacustris is reproductively successful in the Baía River and in the Fechada, Guaraná, Patos, Garças, Ventura and Ressaco do Pau Véio lagoons strengthens the importance of the areas of environmental protection of the islands and lowlands of the Paraná River, Ilha Grande National Park and Ivinheima River State Park.

Chitosan- hypothalamic hormonal analogue nanoconjugates enhanced the reproductive performance in Indian major carp, Labeo rohita

The current study reports the potential of chitosan nanoparticles for the efficient delivery of hypothalamic hormonal analogue in Labeo rohita, aiming to improve reproductive performance. Here salmon gonadotropin-releasing hormone analogue (sGnRH-a) was conjugated with chitosan nanoparticles (ChN-sGnRH-a) to evaluate its efficiency in enhancing the reproductive gene expression, hormones as well as the overall reproductive output in L. rohita. A total of 54 pairs of brooders were selected and divided into six treatments viz; C0: Negative Control (fish injected with bare chitosan nanoparticles), C: Positive Control (fish injected with Gonopro-FH®, a commercially available inducing hormone, at a dose of 0.2 ml/kg body weight of fish), T1: fish injected with ChN-sGnRH-a at a dose of 0.2 ml/kg, T2: T1 + 10 mg/ml domperidone, T3: fish injected with ChN-sGnRH-a at a dose of 0.1 ml/kg, T4: T3 + 10 mg/ml domperidone. In T2 and T4 treatments, serum hormones, Testosterone (T); Estradiol (E2); Vitellogenin (Vtg); and 17α, 20β-dihydroxyprogesterone (17α, 20β-DHP) showed the sustained elevation. The means of reproductive traits like fecundity, fertilization rate, pseudo-gonadosomatic index and spawning rate were significantly (P&amp;lt;0.05) higher in T2 treatment, while no significant difference was found between C and T4 treatment. The mRNA expression level of follicle-stimulating hormone (fshβ), luteinizing hormone (lhβ) and their cognate receptors was significantly better in T2 treatment, while no significant difference was found between T4 and C treatments. Further, the histological analysis of ovaries showed increased post-ovulatory follicles in C, T2 and T4 treatments. The results indicate that ChN-sGnRH-a could help in reducing the recommended dose of sGnRH-a without affecting the reproductive performance in L. rohita females. The sustained releasing mechanism of this formulation may be used as an induced breeding strategy in female L. rohita broodstock.

Oocyte development, packing in the ovary, and spawning pattern of squid Lolliguncula panamensis in the Mexican South Pacific

Squid Lolliguncula panamensis Berry, 1911 is of commercial and ecological importance in the Gulf of Tehuantepec (southeastern Mexico). This study examines the mode of oocyte development, packing in the ovary, and spawning pattern of this understudied species. Lolliguncula panamensis presents a synchronous oocyte growth in batches, with multiple spawnings, with the presence of post-ovulatory follicles and atretic follicles, including the constant presence of pre-vitellogenic and vitellogenic oocytes. The size frequencies of oocytes of ripe ovaries exhibit a pronounced morphological and size separation between the late yolk stage and mature oocytes, suggesting that the oocytes pass through this size range very fast. These oocytes adopt a geometrical shape that makes their packing efficient for spawning. One three-dimensional packing of vitellogenic oocytes (scutoid type) in the ovary was observed. The results of our study suggest that the spawning behavior of Lolliguncula panamensis may constitute an opportunistic reproductive strategy in which individuals present multiple spawnings over a brief period. We suggest that this strategy might be a response to complex regional oceanographic conditions of the Gulf of Tehuantepec.

Dynamic mRNA expression during chicken ovarian follicle development.

Ovarian follicle development is a complex and well-orchestrated biological process of great economic significance for poultry production. Specifically, understanding the molecular mechanisms underlying follicular development is essential for high-efficiency follicular development can benefit the entire industry. In addition, domestic egg-laying hens often spontaneously develop ovarian cancer, providing an opportunity to study the genetic, biochemical, and environmental risk factors associated with the development of this cancer. Here, we provide high-quality RNA sequencing data for chicken follicular granulosa cells across 10 developmental stages, which resulted in a total of 204.57 Gb of clean sequencing data (6.82 Gb on average per sample). We also performed gene expression, time-series, and functional enrichment analyses across the 10 developmental stages. Our study revealed that SWF (small while follicle), F1 (F1 hierarchical follicles), and POFs (postovulatory follicles) best represent the transcriptional changes associated with the prehierarchical, preovulatory, and postovulatory stages, respectively. We found that the preovulatory stage F1 showed the greatest divergence in gene expression from the POF stage. Our research lays a foundation for further elucidation of egg-laying performance of chicken and human ovarian disease.

Involvement of cathepsin L in the degradation and degeneration of postovulatory follicle of the medaka ovary†.

Cathepsin L plays physiological and pathological roles in immune responses, cancer, metamorphosis, and oogenesis in several species. However, the function of Cathepsin L in medaka ovaries remains unclear. Therefore, here, we examined the physiological functions of Cathepsin L in the medaka ovaries. Cathepsin L mRNA transcripts and proteins were found to be constitutively expressed in the ovaries of Oryzias latipes over a 24-h spawning cycle. Expression was localized within the oocyte cytoplasm of growing follicles and the follicle layer of preovulatory and postovulatory follicles. Moreover, the active form of Cathepsin L was highly expressed in the follicle layer of periovulatory follicles and the ovaries 2-6h after ovulation. Recombinant Cathepsin L was activated under acidic conditions and exhibited enzymatic activity in acidic and neutral pH conditions. However, extracellular matrix proteins were degraded by recombinant Cathepsin L under acidic, not neutral pH conditions. Cathepsin L was secreted from preovulatory follicles, while active recombinant Cathepsin L was detected in the conditioned medium of a medaka cell line, OLHNI-2. Mechanistically, recombinant Cathepsin L activates recombinant urokinase-type plasminogen activator-1, which is expressed within the follicle layers post-ovulation. Meanwhile, the treatment of medakas with an E-64 or anti-Cathepsin L antibody effectively blocked follicular layer degeneration and degradation after ovulation, whereas in vitro ovulation was not inhibited by either. Collectively, the findings of this study indicate that although Cathepsin L does not impact ovulation in medakas, it contributes to the degeneration and degradation of the follicle layers following ovulation via activation of urokinase-type plasminogen activator-1, and not via the degradation of extracellular matrix proteins.

Handling Effects on Histological Identification of Female Reproductive Status: Examples from Tropical Deepwater Snappers

Post-mortem ovarian tissue degradation from handling effects, such as delays in preservation, can lead to inaccurate reproductive assessments. Therefore, it is important to understand the differences between handling effects and natural ovarian atresia. Seven treatments of various holding temperatures and times to preservation were applied to whole fish and extracted ovaries of three tropical deepwater snapper species. Ovarian post-mortem degradation was observed at 12 h at ambient temperature and after 48 h iced or refrigerated for both whole fish and extracted ovaries; however, degradation did not adversely affect correct reproductive phase classification in fishes stored in ice from 12 to 48 h post-capture. A clear histological indicator of post-mortem degradation was the breakdown of ooplasm organelles at the oocyte periphery observed in vitellogenic and cortical alveolar oocytes. However, the chorion typically remains intact during post-mortem degradation, in contrast to natural atresia. Effects on post-ovulatory follicles were most discernible after 96 h on ice or refrigeration. Freezing gonadal tissue resulted in drastic changes to oocyte shape and morphology, making reproductive phase classification challenging. We advise that (1) freezing ovaries should be avoided where possible, and (2) gonad tissue should ideally be preserved immediately but no later than 48 h post-capture.

A Quantitative Histologic Analysis of Oogenesis in the Flatfish Species Pleuronectes platessa as a Tool for Fisheries Management.

The following paper gives a detailed description of the oogenesis cycle for the European Plaice (Pleuronectes platessa), from oogonia to post-ovulatory follicle, including ovarian follicle and zona pellucida sizes. Noteworthy particularities were the difficulty in identifying cortical alveoli due to their very small size. Quantitative histology (stereology) on histological slides was used to determine a first size at maturity for females from the English Channel, which was found to be smaller compared to the literature (19 cm). Stereology also determined a first spawning event starting in January, with a peak in February and ongoing until March. Moreover, the use of stereology showed misclassifications for individuals categorized into a maturity phase using a macroscopic visual method. Misclassifications were found with individuals that had spawned (D) but were put under the immature (A) phase, and individuals in development (B) classified under D.

Revisiting the spawning fraction of Pacific bluefin tuna (Thunnus orientalis) caught in the Sea of Japan based on diurnal changes in spawning markers

The spawning fraction (SF) is an important reproductive trait used to assess the reproductive potential of indeterminate spawning fishes. To estimate the SF more accurately, the durations of spawning markers in ovaries need to be determined. The SF of the Pacific bluefin tuna Thunnus orientalis (PBF) in the Sea of Japan (SOJ) is higher than the SFs in its other main spawning grounds. The present study aimed to revisit the SF of the PBF in the SOJ by focusing on diurnal changes in spawning markers and estimating the duration of spawning markers in PBF ovaries. According to diurnal changes in the postovulatory follicle (POF) degeneration process and final maturation process of oocytes, POFs were observed in ovaries up to 38.5 h after ovulation. The revisited total SF throughout the spawning season was 0.34–0.43 in Area 1 and 0.50–0.64 in Area 2; these values are smaller than the SF previously estimated in the SOJ. The estimated SF of the PBF in the present study was equal to or slightly higher than that in the water between the Nansei Islands, Japan, and the northeast of the Philippines and higher than that in the Kuroshio-Oyashio transition area.

Reproductive biology of wahoo (Acanthocybium solandri) in the Canary Islands (eastern-central Atlantic)

The reproductive status of wahoo (Acanthocybium solandri) in the eastern-central Atlantic was investigated to better understand their migration and breeding patterns. The waters around the Canary Islands are considered a breeding area for wahoo; and this study documents the first described breeding activity found in the eastern Atlantic. The presence of many mature and spawning capable wahoo reported in this study confirms its spawning activity in this region. Off the Canary Islands, only mature individuals spawn in the region where no immature individuals were observed to date. Most of the specimens captured in Canary Islands waters exceed 100 cm TL (about 2 years old). Values of the gonadosomatic index (GSI) of males were much lower than those estimated for females. Testes showed little changes in size throughout gametogenesis, while ovaries increased significantly (p<0.05). The low values make it inadvisable to use GSI in males to determine spawning activity. In the Canary Islands, wahoo females spawn (fishes with tertiary vitellogenic oocytes, postovulatory follicles or germinal vesicle migration, yolk coalescence, germinal vesicle breakdown and hydrated oocyte) mainly during a 4-month period in summer. Both females of spawning capable outside the main summer breeding period and females in regressing phase during the spawning period have been observed in the Canary Islands. Males were found in the spawning capable phase throughout the year, with greater prevalence between May and October.

The membrane androgen receptor ZIP9 (SCL39A9) maintains ovarian homeostasis by mediating post-ovulatory follicle breakdown in zebrafish

ZIP9 was recently characterized as a membrane androgen receptor in Atlantic croaker granulosa/theca (G/T) cells where it mediates androgen-induced apoptosis in vitro, but the physiological significance of this action has remained unclear. In the current study, we utilized ZIP9 knockout (zip9-/-) zebrafish to investigate the role of ZIP9-mediated androgen-induced G/T cell apoptosis in vivo. We first confirmed ZIP9 mediates apoptosis of zebrafish G/T cells in vitro. Testosterone increased apoptosis, intracellular free zinc, and expression of pro-apoptotic members bax and p53 in wildtype and zip9+/+ zebrafish G/T cells, but not in ZIP9 knockout and knockdown cell models. We hypothesized ZIP9-mediated G/T cell apoptosis may be involved in post-ovulatory follicle (POF) breakdown in vivo. Post ovulation, zip9, bax, and p53 were upregulated in zip9+/+ but not in zip9-/- ovaries. Immunoreactivity of cleaved caspase 3 was also higher in POFs from zip9+/+ ovaries compared to zip9-/-, and POF breakdown was significantly delayed in zip9-/- fish compared to zip9+/+ counterparts. To determine the detrimental consequences of delayed POF breakdown in the zip9-/- model, fish were challenged with repeated ovulation induction. After the challenge, zip9-/- fish exhibited abnormal ovarian lesions that contained debris consistent with atretic or necrotic cellular material. However, no abnormalities were observed in zip9+/+ fish ovaries, indicating that the abnormal phenotype is due to the loss of ZIP9. This study demonstrates an important role for ZIP9 in mediating POF breakdown and maintaining tissue remodeling and homeostasis in the teleost ovary and indicates a role for the ZIP9-mediated androgen-induced apoptotic response in vivo.

Reproductive biology of yellowfin tuna (Thunnus albacares) in the northcentral U.S. Gulf of Mexico

The reproductive biology of yellowfin tuna (Thunnus albacares) was investigated from fish collected throughout 2000–2017 in the northcentral U.S. Gulf of Mexico (GOM; n = 1135 females, 776 males), predominately from recreational anglers fishing off the Mississippi River (93 %). Histological evidence, along with mean gonadosomatic index (GSI) values, showed that peak spawning occurred from May to August, with the highest mean GSI value for both sexes observed in May (females, 1.52 %; males, 0.57 %). During the reproductive season, the amount of active spermatogenesis in spawning capable males varied monthly as observed by the progression of germinal epithelium (GE) subphases (i.e., early-GE, mid-GE, late-GE), with the mid-GE subphase observed most frequently throughout the peak spawning season. The upper and lower 95 % confidence intervals among length at 50 % maturity (L50) estimates had the largest degree of separation between the physiological (cortical alveoli, L50 =1002 ± 7.18 mm CFL) and functional maturity thresholds (primary or secondary vitellogenesis; L50 =1071 ± 4.89 mm CFL), indicating that the physiological maturity threshold should be used with caution as it may underestimate L50. Using the postovulatory follicle (POF) method, the minimum spawning interval was estimated during peak spawning months for all functionally mature females at 2.10 days, with a minimum of 17.30 % daily spawning. Batch fecundity estimates for 24 females was linearly related to size and ranged from 37,956–6.2 million eggs per batch. These data allow for U.S. GOM reproductive parameter estimates to be incorporated, for the first time, into future Atlantic yellowfin tuna stock assessments done by the International Commission for the Conservation of Atlantic Tunas.