Cortical Alveoli Oocytes Research Articles

The late-evolving salmon and trout join the GnRH1 club

Although it is known that the whitefish, an ancient salmonid, expresses three distinct gonadotropin-releasing hormone (GnRH) forms in the brain, it has been thought that the later-evolving salmonids (salmon and trout) had only two types of GnRH: GnRH2 and GnRH3. We now provide evidence for the expression of GnRH1 in the gonads of Atlantic salmon by rapid amplification of cDNA ends, real-time quantitative PCR and immunohistochemistry. We examined six different salmonid genomes and found that each assembly has one gene that likely encodes a viable GnRH1 prepropeptide. In contrast to both functional GnRH2 and GnRH3 paralogs, the GnRH1 homeolog can no longer express the hormone. Furthermore, the viable salmonid GnRH1 mRNA is composed of only three exons, rather than the four exons that build the GnRH2 and GnRH3 mRNAs. Transcribed gnrh1 is broadly expressed (in 17/18 tissues examined), with relative abundance highest in the ovaries. Expression of the gnrh2 and gnrh3 mRNAs is more restricted, primarily to the brain, and not in the gonads. The GnRH1 proximal promoter presents composite binding elements that predict interactions with complexes that contain diverse cell fate and differentiation transcription factors. We provide immunological evidence for GnRH1 peptide in the nucleus of 1-year-old type A spermatogonia and cortical alveoli oocytes. GnRH1 peptide was not detected during other germ cell or reproductive stages. GnRH1 activity in the salmonid gonad may occur only during early stages of development and play a key role in a regulatory network that controls mitotic and/or meiotic processes within the germ cell.

Reproductive Maturation of Meagre Argyrosomus regius (Asso, 1801) Reared in Floating Cages.

The meagre Argyrosomus regius (Asso, 1801) is a promising aquaculture species that shows reproductive dysfunctions when reared in tanks. The aim of this study was to assess the capacity of meagre, reared in cages under routine farming conditions, to mature gonads and reproduce spontaneously. Meagre adults, reared in a fish farm located in the Gulf of Taranto (Italy), were sampled from March to July 2021. The gonadosomatic index and sex steroid plasma concentrations increased from March-April to June, and then decreased in July. In March-April, most of the females showed perinucleolar or cortical alveoli oocytes as the most advanced stages in the ovaries, and most of the males had testes at early spermatogenesis stage. In June, most of the sampled females had oocytes at late vitellogenesis or early post-vitellogenesis stages, and males had seminiferous tubules filled with spermatozoa. In July, most of the females had signs of previous spawning, and males showed scarce amounts of luminal spermatozoa. The present study demonstrated the capacity of meagre, reared in sea cages under commercial conditions, to carry out gametogenesis and spontaneously release gametes. Meagre reproduction, under routine farming conditions, may represent an opportunity for the expansion of meagre aquaculture production.

Tracking oocyte development and the timing of skipped spawning for north-east Arctic haddock (Melanogrammus aeglefinus).

The present study tracked oocyte development over 9 months and noted incidences of ‘skipping’, i.e., adults terminating their upcoming reproductive cycle, in field‐caught north‐east Arctic (NEA) haddock (Melanogrammus aeglefinus), currently the largest stock of this species. Applications of advanced image and histological techniques revealed the presence of cortical alveoli oocytes (CAO), which prevailed as the most advanced oocyte phase for 4–5 months. This new finding of an extended and early appearance of CAOs in this gadoid was supported by that vitellogenesis first started to appear 3 months later. The subsequent oocyte growth trajectories indicated that larger individuals [total length (TL) = 70 cm] typically spawn in the order of 3 weeks earlier than the smaller ones (TL = 40 cm). The spawning season appeared stretched over about 3 months. The majority of skipping females arrested oocyte growth at the CAO phase followed by atretic reabsorption. Compared to those individuals maturing for the spawning season, ‘skippers’ generally exhibited lower body condition, characterized also by relatively lower liver sizes at the time of the main spawning season. This study demonstrated well‐developed skipping dynamics, but also that the CAO period, i.e., when skipping takes place, may be exceedingly long in this commercially valuable gadoid and that its reproductive cycle in many ways deviates from that of the data‐rich, sympatric NEA cod (Gadus morhua).

Molecular cloning, characterisation and expression analysis of the vitellogenin genes vtgAo1 and vtgC during ovarian development in Chinese hook snout carp Opsariichthys bidens.

Vitellogenesis is essential for oocyte maturation. Vitellogenin (Vtg), a yolk precursor protein, plays an important role in oogenesis and vitellogenesis. Chinese hook snout carp Opsariichthys bidens is an economically important freshwater fish in China whose reproductive and developmental biology are not well understood. In this study, we undertook histological analysis to examine ovary development and oogenesis in O. bidens. The ovaries were divided into Stages II-V and oocytes were divided into perinuclear oocytes, cortical alveoli oocytes, vitellogenic oocytes and mature oocytes. Full-length cDNA sequences were cloned of two vtg genes from the liver of O. bidens, namely Ob-vtgAo1 and Ob-vtgC. Ob-vtgAo1 and Ob-vtgC cDNA are made up of 4136 and 4392 bases respectively and encode proteins containing 1335 and 1250 amino acids respectively. Ob-vtgAo1 contains three yolk protein domains: lipovitellin heavy chain (LvH), phosvitin (Pv) and lipovitellin light chain (LvL), whereas Ob-VtgC contains LvH and LvL, which are incomplete Vtgs. Ob-vtgAo1 and Ob-vtgC mRNA expression was significantly higher in the liver of O. bidens than in all other tissues. In oocytes of Stage II-III ovaries, yolk granules are almost absent and ovarian and hepatic Ob-vtgAo1 and Ob-vtgC expression is low. At Stage IV, the oocyte is filled with yolk granules and ovarian and hepatic Ob-vtgAo1 and Ob-vtgC expression is significantly increased. Collectively, these findings help us better understand vitellogenesis in O. bidens.

Fecundity regulation strategy of the blue jack mackerel, Trachurus picturatus (Bowdich, 1825), off Madeira Island (NE Atlantic)

This contribution intends to verify the type of fecundity regulation of the blue jack mackerel. For this purpose, the oocyte development process was analysed. A total of 158 ovaries were sampled between January 2009 and April 2010 from purse-seiners operating in the Madeira Island waters, NE Atlantic Ocean. Histological analysis and visual image analysis system were used to study the four main criteria applied for fecundity type determination: (1) presence of a hiatus between pre-vitellogenic and vitellogenic oocytes; (2) number of standing stock of advanced vitellogenic oocytes over the spawning season; (3) mean size of standing stock of advanced vitellogenic oocytes over the spawning season; and (4) the incidence of atresia over the spawning season. The analysis of the oocytes size frequency distribution showed that no distinct hiatus could be observed between pre-vitellogenic and vitellogenic oocytes during the spawning season. Considering the whole spawning period but the last month that was poorly sampled, the number of standing stock of advanced vitellogenic oocytes showed no decrease trend along the spawning season, the mean diameter of cortical alveoli oocytes and of the advanced stock of vitellogenic oocytes did not increase over the spawning season and the relative intensity of atresia was always high throughout this period. These findings suggest the blue jack mackerel displays an indeterminate fecundity.

Histological assessment of organs in sexually mature and post-spawning steelhead trout and insights into iteroparity

Steelhead trout (Oncorhynchus mykiss) are anadromous and iteroparous, but repeat-spawning rates are generally low. Like other anadromous salmonids, steelhead trout fast during freshwater spawning migrations, but little is known about the changes that occur in vital organs and tissues. We hypothesized that fish capable of repeat-spawning would not undergo the same irreversible degeneration and cellular necrosis documented in semelparous salmon. Using Snake River steelhead trout as a model we used histological analysis to assess the cellular architecture in the pyloric stomach, ovary, liver, and spleen in sexually mature and kelt steelhead trout. We observed 38 % of emigrating kelts with food or fecal material in the gastrointestinal tract. Evidence of feeding was more likely in good condition kelts, and feeding was associated with a significant renewal of villi in the pyloric stomach. No vitellogenic oocytes were observed in sections of kelt ovaries, but perinu- cleolar and early/late stage cortical alveolus oocytes were present suggesting iteroparity was possible. We documented a negative correlation between the quan- tity of perinucleolar oocytes in ovarian tissues and fork length of kelts suggesting that larger steelhead trout may invest more into a single spawning event. Liver and spleen tissues of both mature and kelt steelhead trout had minimal cellular necroses. Our findings indicate that the physiological processes causing rapid senescence and death in semelparous salmon are not evident in steelhead trout, and recovery begins in fresh water. Future management efforts to increase itero- parity in steelhead trout and Atlantic salmon must consider the physiological processes that influence post-spawning recovery.

Oocyte development and ovarian maturation of the black triggerfish, Melichthys niger(Actinopterygii: Balistidae) in São Pedro e São Paulo Archipelago, Brazil

The oogenesis is a key stage in the reproductive development of an organism, which can be best understood from histological analysis of ovaries in different maturity stages. In order to provide information on the reproductive biology of the black triggerfish, M. niger, in particular on its oogenesis process, this study aimed at identifying and characterizing the oocyte development stages and its organization within the different stages of ovarian maturation based on specimens from São Pedro e São Paulo Archipelago. In this present report, a number of 294 ovaries were histologically analyzed. It was verified that they are composed of ovigerous lamellae containing oocytes at different development stages. Five different stages of oogenesis were identified: young cells, with an average size of 12.9 ìm; previtellogenic oocytes (perinucleolar), with an average size of 53.5 ìm; cortical-alveoli oocytes with an average size of 83.1 ìm; vitellogenic oocytes, with an average size of 160.4 ìm and mature oocytes, with an average size of 289.8 ìm. In addition to the germ cells, some somatic structures were also identified, such as: ovarian wall, follicular cells and blood vessels. Based on the type and number of oocytes observed, four stages of ovarian maturation were identified: early maturation, represented by only 2.2% of the sample; middle maturation, represented by 9.9%; mature, represented by 44.2% and resting, represented by 43.9%. The identification of five oocyte development stages in the ovarians from M. niger, suggested that the specie follows a pattern similar to that described for other marine fish.

Oogenesis, fecundity and condition of Baltic herring (Clupea harengus L.): A stereological study

Herring (Clupea harengus) is a capital breeder that stores energy reserves in muscle tissue. Individual potential fecundity relies on the size and weight of female fish. Poor condition during the maturation process can lead to a heavy down-regulation of fecundity through atresia and, in the extreme, cause skipped spawning. Herring in the Central Baltic Sea exist in a variable environment where food availability fluctuates substantially. Compared to other herring populations their condition is generally poor. In the present study, the oocyte dynamics and fecundity in relation to the condition of Central Baltic herring was investigated. A modern stereological method, the physical fractionator, was used to quantify the number of oocytes in previtellogenic (PG), cortical alveoli (CA) as well as successive vitellogenic (VT1 and VT2) stages in central Baltic herring during ovarian maturation. The potential fecundity, i.e. the number of VT2 oocytes, was low compared to other Atlantic stocks but the relative potential fecundity was higher. The latter decreased by 71% when comparing early-maturing individuals with CA oocytes and late-maturing individuals with VT2 oocytes, suggesting a substantial down-regulation of fecundity. Although determined as spring spawners by otolith hatch type, 15% of the randomly sampled females were characterized by oocytes in CA stage in the prespawning period, indicating skipped spawning. The condition of these females was poor, which might have resulted in skipped spawning. Ovary weight was a good predictor of potential fecundity within maturing stages of females. Combined with estimates of skipped spawning, this ovary weight could be used to estimate egg production thereby improving Central Baltic herring stock-recruitment models.

Histochemical Evaluation of Sexual maturation Phases in Solea solea Wild Marine Populations

The histological analyzes performed in gonad cells to verify the occurrence of changes in their anatomy is of crucial importance in order to characterize the dynamics of the gonads during the sexual maturation phase of its cells in specimens of wild marine populations. These histological data, together with other reproductive data, can be used in the monitoring of marine environments in which the Solea solea (Ishiba et al., 2008) lives, namely, the coastal waters of the Iberian Peninsula, Africa and Mediterranean sea (Ishiba et al., 2008). Therefore, the main objective of this study was to evaluate the several cellular types and its quantities and anatomies (Ishiba et al., 2008). The study was performed using a total of 19 specimens of the species Solea solea, collected between the months of January and March of 2011 in two different locations of the Portuguese coast (Aveiro and Leixões, Portugal). The gonad samples were fixated in Formalin-acetic acid-alcohol (FAA) and processed in accordance to the standard histology protocol (Culling et al., 1985). The slices of the gonads were colored with Haematoxylin and Eosin (H&E) (used in the study of the general structure of the gonads, as well as in the identification and localization of the different cellular types of the gonad epithelium). As a result of the study, we found 7 different types of gonad cells: I oogonia (It is not photographed ); II a Chromatin nucleolus oocytes (Fig.1. A); II b perinucleolar oocytes (Fig.1. B); III cortical alveoli oocytes (Fig.1. C); IV vitellogenic oocytes (Fig.1. D); V maturing oocyte (Fig.1. E); VI ovulated oocyte (Fig.1. F), (Hibiya, et al., 1995). The different cellular phases were found in all the gonad samples analyzed in this study and the results corresponded to those expected: a decrease in the size in the cells of the first cellular type, the oogonia and an increase in the size in the cells of all other cellular types found in the study. Histological and histochemical analyses of the Solea solea can be used in anatomic and pathological evaluations of the physiological condition of the animals, as stated previously for the muscles, where histological changes could be observed (such as: degeneration and atrophy of the muscle bundles). In the future, the analytical determination of histological and histochemical changes in the gonads of Solea solea, in conjunction with other analytical processes, such as in situ analyzes, can potentially be used to determine and accurately characterize the physiological condition of animals sampled in any natural environment.

Ontogeny of Immunoreactive Lh and Fsh Cells in Relation to Early Ovarian Differentiation and Development in Protogynous Hermaphroditic Ricefield Eel Monopterus albus1

Luteinizing hormone (Lh) and follicle-stimulating hormone (Fsh) control many aspects of gonadal development and function in teleosts. In the present paper, the specific antisera against ricefield eel Lhb (Lh beta subunit), Fshb (Fsh beta subunit), and Cga (the common pituitary glycoprotein hormone alpha subunit) were generated, and the cellular localization, initial appearance, and subsequent development of gonadotrophs in relation to early ovarian differentiation and development in the ricefield eel, a protogynous sex-changing teleost, were examined with immunochemistry. Lhb- and Fshb-immunoreactive signals were identified in distinct pituitary cells that occupied primarily the peripheral regions of the adenohypophysis. During ontogeny, Lhb-immunoreactive signals were first detected in the pituitary around 40 days after hatching (dah) when the oogonia transitioned into early primary growth oocytes, and the intensity of immunoreactivity increased concomitantly with the growth of primary oocytes from 60 to 140 dah. During overwintering from 170 to 230 dah, Lhb-immunoreactive signals were significantly decreased when a large proportion of perinucleolus oocytes contained intense Balbiani bodies. In contrast, Fshb-immunoreactive signals were not detectable in the pituitary until around 230 dah (in the spring after hatching) and slightly increased from 285 dah when the late perinucleolus oocytes began to enter the secondary growth phase. Both Lhb- and Fshb-immunoreactive cells were increased when the early cortical alveoli oocytes emerged at 300 dah. The mRNA expression of lhb and fshb coincided with their immunoreactive signals. Taken together, these results suggest that only Lh is involved in primary oocyte growth in ricefield eels, but both Fsh and Lh are important for the secondary ooctye growth.

Histological Study of the Sex-Change in the Skunk Clownfish Amphiprion akallopisos

Sex change in the protandrous fish Amphiprion akallopisos Bleeker, 1853 (F.Pomacentridae) has been ana- lysed. Experiments consisted of placing males together after being separated from their mates, and observe changes in go- nad histology at different periods, in order to identify signs of the sex change process. The presence of a first invagination on the male gonad wall, and the observation of the first cortical alveoli oocytes as an indication of the beginning of the vitellogenesis process, was the first symptom of the sex change, which has been detected after 18 days in one of the males. Period needed for the sex changing process was size independent. The process by which wall invagination is con- verted into ovarian lumen in the future mature ovary is also described.

Reproductive biology of female big‐bellied seahorses

In this study, ovarian morphology, reproductive condition and sex steroid levels were investigated in the big‐bellied seahorse Hippocampus abdominalis, collected by snorkel and SCUBA diving in Wellington Harbour, New Zealand. Within the ovary, oocytes were contained between an outer muscular wall and an inner layer of luminal epithelium. Two germinal ridges ran along the entire length of the ovary. In cross‐section, oocytes were arranged in sequential order of development beginning at the germinal ridges and ending at the mature edge. Ovarian lamellae were absent. Vitellogenic and advanced cortical alveoli oocytes were elongated in shape, whereas maturing oocytes were distinctively pear‐shaped. Mature oocytes were large (2·6 – 4·4 mm in length) and aligned with the animal pole towards the muscular wall. Reproductively mature females were found throughout the year indicating a protracted reproductive season. The gonado‐somatic index was significantly different between all ovarian stages, but the hepato‐somatic index was not. Females with previtellogenic ovaries had significantly higher plasma concentrations of testosterone than females with vitellogenic or maturing ovaries. There was no significant difference in plasma concentrations of testosterone between females with vitellogenic or maturing ovaries, or in plasma concentrations of 17β‐oestradiol between females in all ovarian stages. This study contributes to the knowledge on the reproductive biology of female syngnathids.

Changes in the ovary of the Gulf killifish, Fundulus grandis (Baird and Girard), during seasonal and semilunar spawning cycles

Annual and semilunar ovarian cycles were examined in a wild population of Gulf killifish, Fundulus grandis, from the Alabama (U.S.A.) coast of the Gulf of Mexico. Production of mature eggs was first observed in late February, with the main breeding season beginning by mid‐March and extending into August. The season was punctuated by shorter, typically semilunar, cycles of spawning activity and gamete development that became more pronounced as the season progressed. In September any remaining ovulated eggs and oocytes past the intermediate‐cortical alveolus stage underwent atresia, suggesting that the latter may be the final gonadotropin‐ independent stage of oocyte development in F. grandis. Seasonal proliferation of primary growth phase and cortical alveolus oocytes occurred in late autumn and early winter (October‐January). Vitellogenic oocytes first appeared in early February at the start of a month of intense and rapid vitellogenic oocyte growth prior to the March onset of a new breeding season.