Temporal dynamics of oocyte development, plasma sex steroids and somatic energy reserves during seasonal ovarian maturation in captive Murray cod Maccullochella peelii peelii.

The temporal dynamics of oocyte growth, plasma sex steroids and somatic energy stores were examined during a 12 month ovarian maturation cycle in captive Murray cod Maccullochella peelii peelii under simulated natural photothermal conditions. Ovarian function was found to be relatively uninhibited in captivity, with the exception that post-vitellogenic follicles failed to undergo final maturation, resulting in widespread pre-ovulatory atresia. Seasonal patterns of oocyte growth were characterised by cortical alveoli accumulation in March, deposition of lipids in April, and vitellogenesis between May and September. Two distinct batches of vitellogenic oocytes were found in Murray cod ovaries, indicating a capacity for multiple spawns. Plasma profiles of 17beta-oestradiol and testosterone were both highly variable during the maturation period suggesting that multiple roles exist for these steroids during different stages of oocyte growth. Condition factor, liver size and visceral fat stores were all found to increase prior to, or during the peak phase of vitellogenic growth. Murray cod appear to strategically utilise episodes of high feeding activity to accrue energy reserves early in the reproductive cycle prior to its deployment during periods of rapid ovarian growth.     

Age-related changes in ovarian characteristics, plasma sex steroids and fertility during pubertal development in captive female Murray cod Maccullochella peelii peelii

Age-related changes in ovarian development characteristics and plasma sex steroids in female Murray cod were examined throughout their second, third and fourth years of life to better understand the physiological and endocrine processes associated with puberty in this species in captivity. Spawning performance of 2+ and 3+ year old females was also assessed to identify ontogenetic differences in egg fertility. Puberty was acquired in 38% of 1+ year old females and 100% of age 2+ females. By age 3+, all females had developed full (adult) reproductive function. Ovarian development in pubertal fish was characterised by a rapid transition between cortical alveoli and lipid droplet oogenic phases, coinciding with significantly lower plasma 17β-oestradiol in age 2+ females (p < 0.05). Mean mature oocyte diameter (2.44 mm), post-fertilisation viability (30.80%) and hatchability (0.99%) of eggs from age 2+ females were significantly reduced relative to age 3+ adults (2.81 mm, 84.89% and 23.58%, respectively). Ovaries of pubertal Murray cod exhibited both vitellogenic and ovulatory capacities, yet functional abnormalities during secondary oocyte growth are likely to have contributed to poor egg fertility and consequently, evaluations of age-at-first maturity based on the presence of advanced ovarian stages may overestimate the reproductive potential of younger broodstock populations.     

Fatty acid metabolism in the freshwater fish Murray cod (Maccullochella peelii peelii) deduced by the whole-body fatty acid balance method

The whole-body fatty acid balance method was used to investigate the fatty acid metabolism in Murray cod (Maccullochella peelii peelii) fed diets containing canola (CO) or linseed oil (LO). Murray cod were able to elongate and desaturate both 18:2n-6 and 18:3n-3. In fish fed the CO diet, 54.4% of the 18:2n-6 consumed was accumulated, 38.5% oxidized and 6.4% elongated and desaturated to higher homologs. Fish fed the LO diet accumulated 52.9%, oxidized 37% and elongated and desaturated 8.6% of the consumed 18:3n-3. The overall roles of n-6 fatty acids appeared more important in Murray cod compared to other freshwater species. Murray cod also showed a preferential order of utilization of C18 fatty acid for energy production (18:3n-3 > 18:2n-6 > 18:1n-9). Moreover, it is demonstrated that an increase in dietary 18:3n-3 is directly responsible of increased desaturase activity and augmented saturated fatty acid accumulation in the fish body. The present study also suggests that, in the context of the possible maximization of the natural ability of fish to produce long chain polyunsaturated fatty acids, the whole-body approach can be considered well suited and informative and Murray cod is a suited candidate to fish oil replacement for its diets.     

A correlation between juvenile hormone deficiency and vitellogenic oocyte degeneration inDrosophila melanogaster

Summary It is known from previous work that juvenile hormone (JH) is required to initiate vitellogenin uptake into maturing oocytes ofDrosophila melanogaster, but additional requirements for this hormone during oocyte maturation have not been fully understood. To determine if early vitellogenic oocytes (stages 8 and 9) require JH for continued development, these oocytes were transplanted toDrosophila female and male hosts which were rendered deficient in JH by three methods. Implanted stage 9 and usually stage 8 oocytes were found to degenerate in JH-deficient hosts unless ZR-515, a JH analogue, was applied to the host shortly after implantation.These results were confirmed during in situ ovary development. JH deficiency was produced in gravid females, and ovaries examined at subsequent time intervals were found to be deficient in stage 8–10 oocytes as early as 6 h after treatment. Degenerating oocytes corresponding to these stages were commonly found. ZR-515 prevented oocyte degeneration during at least the first 8 h and continued to support stage 8–10 oocyte development 24 h after application to these females. The results suggest that JH is required not only for initiation but also for continuation of vitellogenin uptake and oocyte development.     

Do fast increasing food conditions promote the midsummer decline of Daphnia galeata?

Ovaries from mature giant red shrimp Aristaeomorpha foliacea were investigated histochemically and ultrastructurally. Four growing stages of the oocytes were distinguished: premeiosis stage, previtellogenetic stage, early vitellogenic stage and late vitellogenic stage. In addition, occasional resorptive oocytes were found. Oogonia and premeiotic oocytes were found in germinative zones. Previtellogenic and vitellogenic oocytes were localized in maturative zones. As vitellogenesis proceeded, oocytes showed a progressive development in the number of lipid droplets as well as in the extension of RER, constituted of dilated cisternae, uniformely scattered throughout the cytoplasm. The RER produced yolk granules and a lampbrush-like substance. The latter was released under the oolemma and constituted a characteristic cortical zone. The oolemma did not develop microvilli or micropinocytotic vesicles to incorporate yolk precursors. Thus, the protein yolk appeared to be of endogenous origin. Few somatic cells were found around the oocytes, but they never gave place to a continuous epithelial layer around oocytes, thus it is not possible to speak of ovarian follicle. The cytoplasm of these mesodermal-oocyte associated cells (MOAC) was characterized by a typical steroidogenic apparatus. Few resorptive immature oocytes were found inside late vitellogenic oocytes. Since the ovaries were packed with late vitellogenic oocytes and the few immature oocytes were hardly detectable, oocyte maturation occurred in a synchronous way.     

Expression Patterns of CREBs in Oocyte Growth and Maturation of Fish

In fish, oocyte meiotic maturation is regulated by 17α, 20β-dihydroxy-progesterone through cAMP. To study the role of cAMP response element binding protein (CREB) in meiotic maturation, we cloned and characterized the expression pattern of CREBs from two fish models, the Nile tilapia and catfish. In the Nile tilapia three different CREBs were identified where in CREB1 was found in many tissues including gonads with abundant expression in testis. CREB2, few amino acids shorter than CREB1, was expressed in several tissues with abundant expression in ovary. In addition, a 3’UTR variant form, CREB3 was exclusively found in ovary. During natural 14-day ovarian cycle of the Nile tilapia, CREB1 expression was stable throughout vitellogenesis with a sharp decrease on the day of spawning. In contrast, CREB2 remain unchanged throughout the ovarian cycle, however elevated in 11-day full-grown immature ovarian follicle and after hCG-induction. Interestingly, CREB3 expression was induced three folds on the day of spawning as well as during hCG-induced oocyte maturation. Based on the synergistic expression pattern, CREB1 is likely to control oocyte growth, whereas CREB 2 and 3 contribute to oocyte maturation in tilapia and the latter seems to be critical. In catfish, a single form of CREB showed a maximum expression during spawning phase and hCG-induced maturation both in vivo and in vitro augmented CREB expression. These results suggest that spatial and temporal expression of CREBs seems to be important for final oocyte maturation and may also regulate oocyte growth in fish.     

Cytochemical characterisation of the leucocytes and thrombocytes from Murray cod (Maccullochella peelii peelii,Mitchell)

Cytochemistry has proven effective in differentiating specific cell lineages and elucidating their functional properties. This study utilised a range of cytochemical techniques to further investigate the leucocyte populations from Murray cod, an iconic Australian teleost fish species. This analysis provided clear insight into the structure and function of the leucocytes from this fish, which were found to be broadly similar to those of other fish species. However, some important differences were identified in Murray cod, such as the presence of naphthol AS chloroacetate esterase activity in the heterophil population, positive staining for periodic acid Schiff's, alkaline phosphatase and Sudan black B in the lymphocyte population, and a prevalent population of myeloid precursor cells.     

Relations Between Hibernation and Ovarian Functions in a Temperate Zone Frog,Rana temporaria

Adult female frogs were exposed to artificial hibernation in a refrigerator, at about 1–3°C, 1–2 months earlier than in nature, isolated or together with males. Ovarian functional state at the beginning of hibernation was assessed from ovarian biopsies taken in mid-September. All frogs ovulated during hibernation which was interrupted in mid-May, but in seven out of 19 frogs ovulation was incomplete. The number of non-ovulated oocytes varied from a minor fraction to about two thirds of the complement of vitellogenic oocytes, indicating that the follicle size reached at the time of induced hibernation was at the critical level for successful maturation. This critical size was about half the normal oocyte volume at the onset of natural hibernation. There was no vitellogenic growth during hibernation, which presumably constitutes the period of follicle maturation. In five of the frogs, oogenesis sensu stricto had occurred during the period of hibernation, some oogenic events being completely finished at autopsy in mid-May and others still progressing.     

Reproductive biology ofAwaous guamensis, an amphidromous Hawaiian goby

Synopsis Spawning season, size at first reproduction, oocyte maturation, and fecundity ofAwaous guamensis, an amphidromous Hawaiian goby, were studied from June 1989 through May 1991 in the Wainiha River, Kau'ai, Hawai'i. Female fish larger than 73 mm standard length (SL) had mature gonads from August through December in 1989 and 1990. Gonadosomatic index (GSI) values for mature females ranged from 0.2 to 14.5 during the spawning season. Male fish larger than 64 mm SL had elevated GSI values from June 1989 through December 1989 and from August 1990 through December 1990. Mature sperm were found in two male fish collected in January and February. GSI values for mature males ranged from less than 0.01 to 4.0 in the spawning season. Size-frequency distributions of measurements of vitellogenic oocyte diameters and microscopic observations of oocytes indicated this species has group-synchronous oocyte development. Ovarian maturation stages examined over a 29-month period suggest that members of the stock spawned at different times within the spawning season, although mass spawning events have been documented for this species. Estimates of clutch sizes from nests measured in situ were comparable to estimates of potential fecundity from in vitro examination of ovaries, and indicated that female fish deposited an entire clutch during a spawning event. No evidence for multiple spawning by an individual fish in a single season was found. However, microscopic observations of brown bodies in some ovaries suggested that individual fish probably spawn more than once in a lifetime.     

Cytodifferentiation of ovarian follicle cells during oocyte growth and maturation

Inasmuch as 17α,20β-diOHprog was identified as the maturation-inducing hormone, we now have two known biologically important mediators of oocyte growth and maturation in salmonids, estradiol-17β and 17α,20β-diOHprog. It is now established that the granulosa cells are the site of production of these two mediators, but production by the ovarian follicle depends on the provision of precursor steroids by the thecal cell (two-cell type hypothesis). A dramatic switch in the steroidogenic pathway from estradiol-17β to 17α,20β-diOHprog occurs only in ovarian follicle cells immediately prior to oocyte maturation. This switch is a prerequisite step for the growing oocyte to enter the maturation phase. Resolution of the molecular events regulating this switch will provide new insight into the hormonal events regulating oocyte growth and maturation.     

Biomanipulation: a review of biological control measures in eutrophic waters and the potential for Murray cod Maccullochella peelii peelii to promote water quality in temperate Australia

Biomanipulation is a method of controlling algal blooms in eutrophic freshwater ecosystems. The most common approach has been to enhance herbivores through a reduction of planktivorous fish and introduction of piscivorous fish. The method was originally intended to reduce grazing pressure on zooplankton, thereby increasing grazing pressure on phytoplankton to increase water clarity and promote the growth of aquatic macrophytes. Biomanipulation has received considerable attention since it was proposed in 1975 where innovative approaches and explanations of the processes have been developed. Although many successful biomanipulation exercises have been conducted internationally, it has received comparatively little attention in the Southern Hemisphere and has not been trialled in the southern temperate climate of South Australia. This is a review to speculate upon the criteria for and against the application of biomanipulation in southern temperate Australia using the native species Murray cod (Maccullochella peelii peelii) and to suggest future research.     

Comparative study of reproductive biology in single and multiple-spawner cyprinid fish. II. Sex steroid and plasma protein phosphorus concentrations

The dynamics and regulation of oogenesis in single and multiple-spawner cyprinid fish showing group-synchronous oocyte development, was investigated in three species from the River Meuse (Belgium): the roach Rutilus rutilus as a single spawner, and the bleak Alburnus alburnus and the white bream Blicca bjoerkna as multiple spawners. This paper compares the seasonal profiles of sex steroids (oestradiol-17β, testosterone and 17,20β-dihydroxy-4-pregnen-3-one) and plasma alkali-labile protein phosphorus. Different patterns of plasma oestradiol-17β (E2) and plasma protein phosphorus (PPP) have been observed not only between the single and the multiple spawner fish, but also among the two multiple spawners. In roach, two increases of E2 levels were observed. The first occurred in September after a short gonadal quiescent period, and coincided with the increase of the PPP at the onset of exogenous vitellogenesis. The second took place in spring before the spawning season. The low PPP recorded during that period probably reflected its rapid incorporation by the oocytes. In both multiple spawners, highest values of PPP were recorded just before the spawning season. In white bream, the PPP declined progressively once the differentiation of exogenous vitellogenic oocytes was completed before the onset of the spawning season. In bleak, PPP levels remained high throughout the spawning season and corresponded to a sustained oocyte recruitment during the whole of this period. Regardless of the pattern of oocyte growth recruitment, the E2 concentrations were high in both multiple spawner species during the breeding season. In the three species, testosterone levels remained low regardless of the maturation stage (ranging from 0.6 to 13.4ng ml^?1). Except for relatively high concentrations of 17,20βP in roach during final maturation and postspawning stages (20 and 28 ng ml^?1, respectively), low levels of this steroid were measured in these cyprinids, and especially in the multiple spawner fish. The role of this progestogen as the maturation inducing Steroid is discussed.     

Vitellogenesis in Varroa jacobsoni,a parasite of honey bees

Reproduction in Varroa jacobsoni occurs only in cells of the capped honey bee brood. Female mites were sampled at different times after cell sealing and ovaries containing a vitellogenic oocyte of the first gonocycle were examined under an electron microscope. It was found that the cytoplasmic connection between the lyrate organ and the oocyte persists far into the vitellogenic growth phase. In addition, a large amount of yolk material is taken up from the haemolymph. All ultrastructural features characteristic of vitellogenesis, such as microvilli, coated pits, vesicles and growing yolk platelets, are present. If more than four Varroa females live in an overcrowded brood cell, they appear to be in stress conditions and their vitellogenic oocytes may become atretic. Alterations typical for oocyte degradation and oosorption were observed in such situations.     

Oogenesis and the ovarian cycle in Salamandra salamandra infraimmaculata Mertens (Amphibia; Urodela; Salamandridae) in fringe areas of the taxon's distribution

Reproductive cycle and oogenesis were studied in specimens of Salamandra salamandra infraimmaculata Mertens that inhabit fringe areas of the taxon's distribution in the Mediterranean region. Both ovarian mass and length are correlated significantly with body mass and length. Ovarian length is also correlated with the number of oocytes. During the oogenetic cycle six stages in oocyte development were recognized. Three occur during previtellogenesis: stage 1, in which oogonia divide and form cell nests; stage 2 in which oogonia differentiate into oocytes; and stage 3, in which the oocyte cytoplasm increases in volume. In the vitellogenic phase two additional stages, 4 and 5, were recognized: stage 4, in which lipid accumulates in vacuoles in the periphery followed by the appearance of yolk platelets near the cytoplasmic margin; and stage 5, in which oocyte volume increases rapidly due to increased number of yolk platelets until it reaches its maximal size. During postvitellogenesis one stage was recognized: stage 6, in which the beginning of maturation is characterized by movement of the nucleus toward the animal pole. Oogenesis continues year-round. The first four stages were seen in all ovaries examined. The ovarian cycle is independent of season and reproductive stage apart from the number of mature, postvitellogenic oocytes that increases following gestation toward the beginning of spring (March-April). J. Morphol 231:149–160, 1997. © 1997 Wiley-Liss, Inc.     

Polymorphic microsatellite loci for species of Australian freshwater cod, <Emphasis Type="Italic">Maccullochella</Emphasis>

The Australian freshwater cod genus, Maccullochella is represented by three species: Murray cod, M. peelii peelii, eastern freshwater cod, M. ikei, and trout cod, M.macquariensis. Seven novel microsatellite loci from M. ikei and six previously published loci from M. peelii peelii were tested on wild populations of Murray, eastern and trout cod. Levels of polymorphism varied between species with 13 loci polymorphic in Murray cod, 9 in trout cod and 7 in eastern cod. Observed heterozygosities ranged from 0.053 to 0.842. This suite of microsatellite loci will facilitate future studies of the genetic status of wild and hatchery bred populations of Maccullochella.     

The neuroendocrine regulation of the human ovarian cycle.

The menstrual cycle is now thought to be mainly determined by the ovary itself, which sends various signals to the pituitary and the hypothalamus. The hypothalamus is an autonomous pacemaker, with a pulse frequency that is modulated by ovarian signals; in turn, it is indispensable to ovarian function. In women, the ovarian cycle produces a single mature oocyte each month from puberty to menopause. This follicle is rescued from atresia, the genetically controlled ovarian apoptosis (or "programmed cell death"), involving 99.9% of the follicles. Follicular growth and maturation are mostly independent of gonadotropins from the stage of primordial to antral follicles. A complete intraovarian paracrine system is implied in this gonadotropin-independent follicular growth and in the modulation of the action of gonadotropins in the ovary. Follicle-stimulating hormone (FSH) allows the rescue of a minority of follicles from atresia and is indispensable only for the final maturation of the preovulatory follicle during the follicular phase of the cycle. Luteinizing hormone (LH) is responsible for the final growth of the dominant follicle in the late follicular phase. the induction of ovulation during the LH peak, and the survival of the corpus luteum during the luteal phase. The cyclical variations of gonadotropins are under the control of ovarian steroids (estradiol and progesterone) and peptides (inhibins). The cycle length is determined by the duration of terminal follicular growth and by the fixed life span of the corpus luteum. The ovarian cycle can be monitored as well at the level of target tissues of steroids, such as the endometrium. In fact, the endometrial maturation is synchronized to follicular development, and this synchronization is indispensable for successful implantation of the embryo. The improving knowledge of follicular and endometrial physiology will allow the development of new treatments of infertility, the design of new contraceptive techniques, and a better tolerance of treatments using sex steroids.     

Gonadal development and sex steroids in a female Arctic charr broodstock

Gonadal development and plasma levels of sex steroids were investigated in female Arctic charr at 3-week intervals over a 12-month period. Circulating levels of oestradiol-17β (E₂), testosterone (T) and 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P) were measured by radioimmunoassay, and gonadal status assessed through histological examination and measurement of gonadosomatic index (GSI) and frequency distribution of oocyte size-classes. Gonadal recrudescence during March-July was characterized by modest but insignificant increases in plasma levels of E₂ (2–4 ng ml^?1) and T (2–5 ng ml^?1) and recruitment of oocytes into yolk accumulation. Only a small and insignificant rise in GSI and no apparent increase in oocyte diameter occurred during this period, indicating that the rate of yolk formation and oocyte growth was low. Following transformation from stage V (peripheral yolk granule stage) to stage VI (yolk granule migration stage) in late July, the vitellogenic oocytes entered a phase of rapid growth which resulted in a marked rise in GSI until ovulation commenced in late September. Gonadal growth during this period was accompanied by increases in plasma levels of E₂ and T which peaked at 11 ± 1 (mid-August) and 71 ± 5ng ml^?1 (late September), respectively. The levels of both steroids dropped rapidly during final maturation and ovulation, followed by a surge in plasma levels of 17,20β-P which peaked at an average of 74 ± 17 ng ml^?1 in early October. All three steroids returned to basal levels within a month after ovulation, and all steroids, except E₂, remained low until March of the following year. A slight increase in E₂ detected in February and March during the second season may have been associated with recruitment into vitellogenesis of a new generation of oocytes. It is suggested that the abrupt increase in vitellogenesis in late July may reflect a condition-dependent decision to proceed with maturation, once the energy reserves have been repleted during spring-early summer.     

Qualitative and quantitative changes in hemolymph proteins during an ovarian cycle and after insemination in Thermobia domestica (packard) (thysanura,lepismatidae)

Qualitative and quantitative investigations on the hemolymph proteins in the adult firebrat Thermobia domestica were performed during an ovarian cycle in inseminated and noninseminated females. Variations of hemolymph protein concentration were determined by Lowry's method. In addition, the proteins were studied by gradient slab gel electrophoresis using nondenaturing conditions and microdensitometry. Besides five major protein fractions, which are present in both sexes, three female-specific protein bands (vitellogenins) are found in the hemolymph and in maturing oocytes. These vitellogenins have molecular masses of 430, 300 and 240 kiloDalton. In fact, associated with the main 300-kD band, there were two smaller bands (320 and 280 kD) indistinguishable by densitometric measurement. Quantitative changes of vitellogenins are linked to oocyte maturation. These proteins appeared in the hemolymph before ecdysis, at the same time as the first yolk granules in the basal oocytes. They increased after ecdysis during the intense vitellogenic phase and decreased during chorion formation. In noninseminated females, in which all maturing oocytes are resorbed before chorion formation, the level of the 300 kD vitellogenins remained lower than in inseminated females. The quantity of vitellogenins fell only after complete oosorption. Thus insemination caused changes in the relative quantities of the different vitellogenic proteins.     

Gonadotropin-induced steroidogenic shift towards maturation-inducing hormone in Japanese yellowtail during final oocyte maturation

Intact ovarian follicles, obtained from untreated and human chorionic gonadotropin (HCG) treated Japanese yellowtail Seriola quinqueradiata during different maturational stages, were incubated with radioactive [3H]pregnenolone, [³H]17‐hydroxyprogesterone or [¹⁴C] androstenedione and steroid metabolites identified by thin layer chromatography (TLC) followed by recrystallization to constant specific activity. In untreated late vitellogenic (0 h) follicles, androstenedione was the major product with smaller amounts of testosterone and oestradiol‐17α. In post‐vitellogenic (12 h post‐injection) intact follicles, androstenedione predominated, and although testosterone and oestradiol‐17α were not produced, there were small amounts of 17, 20β‐dihydroxy‐4‐pregnen‐3‐one (17,20β‐P) and 17,21‐dihydroxy‐4‐pregnene‐3, 20‐dione (11‐deoxycortisol). In HCG‐treated fish, a steroidogenic shift resulted in the disappearance of testosterone and oestradiol‐17 coinciding with the appearance of 17, 20β‐P. During early and late final oocyte maturation FOM (24 and 36 h post‐injection), there was a five‐ to seven‐fold increase in the production of 17, 20β‐P, whereas production of 11‐deoxycortisol remained almost the same. During FOM, in addition to 17,20β‐P, its 5β‐reduced metabolite, 17,20β‐dihydroxy‐5β‐pregnan‐3‐one (5β‐17,20β‐P) was synthesized, suggesting a decrease in maturation‐inducing 17,20β‐P activity. 17, 20β,21‐Trihydroxy‐4‐pregnen‐3‐one (20β‐S) was not synthesized by ovarian fragments in Japanese yellowtail at any maturational stage. The metabolites identified on TLC during FOM were tested to evaluate their maturation‐inducing activity in an in vitro bioassay. Of the steroids tested, 17,20β‐P was the most effective inducer of germinal vesicle breakdown (GVBD), followed by 5β‐17,20β‐P. Timely synthesis of 17,20β‐P immediately prior to and during FOM as well as its great potency in inducing GVBD in vitro supports the evidence for a physiological role of 17,20β‐P as a maturation‐inducing hormone in Japanese yellowtail.