Comparison of the gonadal development and plasma levels of sex steroid hormones in diploid and triploid sea bass, Dicentrarchus labrax L

The goal of this study was to compare the reproductive physiology of triploid and diploid European sea bass (Dicentrarchus labrax L.). Gonads of diploid and triploid fish (males and females) were examined both microscopically and macroscopically, together with the plasma levels of the major sex steroids produced (testosterone and estradiol-17beta) when fish were adults. Prior to sexual maturation, the gonadosomatic index (GSI) of triploid males was similar to that of diploids. However, the GSI in 4-year-old adult triploid males was 1.8 times lower than that of diploids (P < 0.05). All diploid males exhibited normal gonadal development. In contrast, in triploid males spermatogenesis was impaired during late meiosis, affecting severely spermiogenesis. This was achieved by an increasing imbalance in the amount of DNA present in daughter cells of the same type as spermatogenesis progressed, as demonstrated by abnormal cell sizes, culminating in inviable spermatids. Thus, no spermiating triploid fish were observed during 4 years, which included three full consecutive maturation cycles. Furthermore, the germ cells from triploids were significantly larger than those from diploids (P < 0.001). Seasonal profiles of plasma levels of testosterone in 4-year-old males were essentially similar in both ploidies. On the other hand, triploid females had rudimentary ovaries containing oogonia and primary oocytes that were arrested during meiotic prophase I, while diploid females exhibited all stages of ovarian development. Diploid females showed levels of testosterone and estradiol-17beta significantly higher than those of triploids (P < 0.05), in which no endocrine signs of maturation were observed at all. Regarding sex ratios, triploids had 10% more females than diploids (P < 0.05) but in both ploidies males predominated, as is usually found in this species under culture conditions. These results show that triploidy blocked the initial phases of meiosis in females and the latter ones in males, resulting in the absence of or reduced gonadal development, respectively. In conclusion, we provide an explanation for the lack of gonadal development in triploid male fish, and, to the best of our knowledge, we report for the first time a case in which induced triploidy completely blocks meiosis in both sexes, thus conferring functional sterility in the sea bass.     

Social control of terminal phase transition in primary males of the diandric wrasse, <Emphasis Type="Italic">Halichoeres poecilopterus</Emphasis> (Pisces: Labridae)

In many diandric fishes, large territorial males with bright body coloration (terminal phase (TP) males) are derived either from initial phase (IP) females that change sex to male or from IP primary males that change color and behavior, but do not change sex. The mechanism controlling the transition of IP primary males into TP males is not well understood. We conducted cohabitation experiments to examine social conditions favoring TP transition by primary males in the diandric wrasse, Halichoeres poecilopterus. IP primary males always started TP-specific sexual behavior in the presence of a smaller subordinate, and subsequently acquired TP body coloration. In contrast, primary males under subordinate conditions often performed female-like sexual behavior. In pairs with similar body sizes, both individuals initiated TP male behavior. The results suggest that TP transition in primary males may be closely related to a dominance relationship (or size order) within social groups, as it is in the case of sex change by females.     

Annual physiological changes in individually housed squirrel monkeys (Saimiri sciureus)

This study investigated whether annual changes in physiology occur in individually housed squirrel monkeys (Saimiri sciureus). Physiological measures were monitored for 20 months. Over the course of the study, all individually housed males and females exhibited clear annual changes in gonadal and adrenal hormone levels, and males exhibited species‐typical changes in body weight. Females exhibited a typical pattern of hormonal changes, with elevations in gonadal steroids occurring during the same months as elevations in cortisol. Males, however, exhibited an atypical pattern, as elevations in hormone levels were not synchronized with each other; rather, elevations in testosterone occurred out of phase with changes in cortisol and body weight. The timing of annual events in individually housed subjects was compared to that in nearby social groups, in which the timing of the breeding season from year to year was determined by social group formations and was outside the naturally occurring breeding season. Elevations of ovarian and adrenocortical hormones in individually housed females were synchronized with indices of breeding in heterosexual social groups. Similarly, weight gain in males was associated with elevations in cortisol and, as with socially housed males, tended to precede seasonal breeding in the social groups. In contrast, annual testosterone elevations for individually housed males were not synchronized with breeding in nearby social groups. We conclude that direct physical interaction is not required for the annual expression of breeding readiness. Synchrony of seasonality among squirrel monkeys may be accomplished by distant social cues in females, but males may require physical interaction for complete synchrony of annual physiological changes. Am. J. Primatol. 47:93–103, 1999. © 1999 Wiley‐Liss, Inc.     

Aromatase inhibitor induces complete sex change in the protogynous honeycomb grouper (Epinephelus merra)

The protogynous hermaphrodite fish change sex from female to male at the certain stages of life cycle. The endocrine mechanisms involved in gonadal restructuring throughout protogynous sex change are not clearly understood. In the present study, we implanted maturing female honeycomb groupers with nonsteroidal aromatase inhibitor (AI), Fadrozole (0, 1, and 10 mg/fish) and examined changes in gonadal structures and serum levels of sex steroid hormones 2(1/2) months after implantation. The ovaries of control females had oocytes undergoing active vitellogenesis, whereas AI caused females to develop into functional males. These males had testes, which were indistinguishable in structure from those of normal males, but bigger in size, and completed all stages of spermatogenesis including accumulation of large amount of sperm in the seminiferous tubules. AI significantly reduced the serum levels of estradiol-17beta (E2) and increased levels of testosterone (T), 11-ketotestosterone (11-KT), and 17alpha, 20beta-dihydroxy-4-pregnen-3-one (DHP). Further, AI suppressed in vitro production of E2, and stimulated the production of T and 11-KT in the ovarian fragments of mature female. In the honeycomb grouper, suppression of both in vitro and in vivo production of E2 and degeneration of oocytes by AI suggests that AI induces complete sex change through inhibition of estrogen biosynthesis, and perhaps, subsequent induction of androgen function.     

Effects of catecholamines on ovary morphology, blood concentrations of estradiol-17beta, progesterone, zinc, triglycerides and rate of ovulation in domestic hens

The present study is an attempt to shed more light on the role of epinephrine (EP) and norepinephrine (NE) in regulating ovarian follicular development, folliculogenesis and ovulation in laying hens. Sixty Egyptian local cross females (Mandarah), 50 weeks old, were individually housed and equally divided into three treatments: control (saline, 0.9% NaCl), EP (0.15 mg epinephrine/hen/day) and NE (0.75 mg norepinephrine/hen/day) (n=20). Animals were injected intramuscularly once a day for 15 successive days. At the end of the experimental period, 10 females from each treatment were randomly chosen, weighed and killed by decapitation. Ovaries and oviducts and ovarian follicles were examined. Plasma concentrations of estradiol-17beta, progesterone, zinc and triglyceride were determined. Results indicated that the ovaries of NE- and EP-treated hens were more developed than those of control hens being heavier and containing more yellow yolk-filled follicles. EP or NE significantly increased the ovulation rate and plasma concentrations of estradiol-17beta, progesterone, zinc and triglyceride compared with control treatment. It could be concluded that catecholamines may have a part in promoting ovarian follicular development and in stimulating ovulation in laying hens at the end of their reproductive lives.     

Gonadal sex reversal in triploid rainbow trout (Oncorhynchus mykiss).

Sex determination in salmonids is primarily governed by sex chromosomes; however, phenotypic expression and successful development of the gonads may be influenced by additional factors. Exposure to exogenous steroids during the critical period of gonadal differentiation will reverse the expected phenotypic sex of both female and male trout. Triploidy, a viable condition in rainbow trout (RBT), alters the degree of gonadal development in a gender-specific manner. Males produce testes with similar morphology and function as diploid fish, but females produce underdeveloped ovaries devoid of growing oocytes. One possible explanation for this observed gender difference is that the timing of meiotic initiation may influence ovarian/testicular development in triploid RBT. To determine whether the early entrance of germ cells into meiosis results in the lack of ovarian development in triploid females, the objective of this study was to sex-reverse genotypic triploid female RBT (XXX) into phenotypic males and genotypic triploid male RBT (XXY) into phenotypic females. Male fish were exposed to estradiol-17beta (E(2)) and females were exposed to the non-aromatizable androgen 17alpha-methyldihydrotestosterone (MDHT). Over 90% of the male fish treated with exogenous E(2) developed gonadal structures indistinguishable from the gonads of triploid females. Triploid female RBT treated with MDHT developed testes; however, not all fish treated with this androgen were completely sex reversed. The results of this investigation are consistent with the hypothesis that the failure of ovarian development in triploid RBT is due to the early onset of meiosis and does not appear to be due to genotypic sex. J. Exp. Zool. 284:466-472, 1999.     

Sex differences in the energetic content of reproductive tissues in the Blackeye Goby,Rhinogobiops nicholsii

Differential energetic investment in reproduction between the sexes has been a driving a force of life history theory and sexual selection. However, reproductive costs between the sexes have often been based on morphology, such as gonad mass and gonadosomatic indices (GSI), and few have directly measured the energy content of gonadal tissues in relation to GSI. Using the blackeye goby, Rhinogobiops nicholsii, we measured the energetic content of whole gonadal tissues, specifically testes, ovaries and associated reproductive tissues using oxygen bomb calorimetry. The energy content per gram unit of gonadal tissues was generally predictive of GSI, indicating that GSI is a reasonable measure of energetic costs. Interestingly, although females had greater gonadal mass, GSI and energy content per gram than males, the sex difference in energy content per mass unit was only 13 %, suggesting that gross indices such as gonadal mass or GSI may overestimate energetic costs where instead the cost difference in a unit gram of gonadal tissues between the sexes is smaller than often predicted. This study also demonstrates that although the cost of ovaries is greater than testes, males’ investment in reproductive tissue can be considerable, which is consistent with the often inflated reproductive success for males in haremic mating systems.     

Examination of the ability of gonadal sex change in primary males of the diandric wrasses Halichoeres poecilopterus and Halichoeres tenuispinis: estrogen implantation experiments

Primary males that function as males throughout their lives are often found among protogynous fishes such as wrasses and parrotfishes. However, the issue of whether the sexuality of primary males involves gonochorism or hermaphroditism remains uncertain. To clarify this, we implanted estradiol-17beta (E2) into the body cavities of primary males of two protogynous wrasses, Halichoeres poecilopterus and Halichoeres tenuispinis. At 51-63 days after implantation, primary males with E2 treatment in both wrasses were observed to develop ovarian tissues. These results suggest that primary males of Halichoeres wrasses potentially have the ability to change sex and that estradiol-17beta is related to gonadal transitions in primary males.     

Reproductive biology of Raja clavata (Elasmobranchii: Rajidae) from Southern Black Sea coast around Turkey

Specimens of Raja clavata were monthly collected at the coast of Havaalan? (Trabzon/Turkey) from January 2009 to December 2009 at depths between 20 and 40?m. A total of 230 individuals of thornback ray (131 females and 99 males) were collected by bottom trawls during research cruises. Using logistic regression, it was determined that TL at 50% maturity of males was 718?mm TL and of females 746?mm TL. The ovarian fecundity ranged from 27 to 60 yellow follicles in both ovaries. Females carrying egg cases were found in July and October. Variations in the gonadosomatic and hepatosomatic indices indicated a continuous reproductive cycle during the year.     

Biochemical and hormonal characterization of follicles from follicular and luteal phase ovaries of goat and sheep.

Follicles from goat and sheep ovaries were characterized for their biochemical and hormonal parameters to investigate the effect of developmental stage of follicles on ovarian steroidogenesis. The follicles were isolated mechanically from follicular and luteal phase ovaries and divided in 6 morphologically different groups (small, medium and large follicular and small, medium and large luteal). Follicles were characterized for their contents of protein, DNA, estradiol-17 beta and progesterone and the activity of 3 beta-hydroxysteroid dehydrogenase. There was a progressive increase in the contents of all these biomolecules and activity of the enzyme as size of follicles increased in both the follicular and luteal phase ovaries. Follicles from follicular phase ovaries exhibited higher estradiol-17 beta content than those shown by luteal phase follicles. The reverse pattern was obtained for progesterone content. The results provide the basic data on biochemical and hormonal entities at different stages of follicular development in small ruminants which may be useful for in vitro studies on regulation of follicular development and steroidogenesis.     

The life history characteristics of Neosebastes pandus and the relationship between sexually dimorphic growth and reproductive strategy among Scorpaeniformes

Scorpaeniformes are an important component of commercial and recreational fisheries world-wide. The Neosebastes species, found in the western Pacific and south-east Indian Ocean, have received little attention from a research perspective. Samples of the bighead gurnard perch, Neosebastes pandus, collected from the lower west and south coasts of Western Australia, were used to undertake the first comprehensive investigation of the biological characteristics of a Neosebastes species. Opaque zones in sectioned sagittal otoliths were validated as forming annually. Female N. pandus grow to a significantly larger size, on average, than males and dominate the largest size classes, while males, growing to a smaller size, accumulate in the intermediate size classes. Although males were far less numerous than females in those age classes in which both sexes were found, males and females attain similar maximum ages >25 years. Neosebastes pandus spawns over a brief period between May (austral late autumn) and July (austral mid-autumn) when water temperature and day length are declining. The mean monthly gonadosomatic indices (GSI, I_GS) values of females during the spawning period are 37–50 times higher than those of males, which mature at an earlier age and smaller length compared to females. Histological examination of the ovaries of females indicate that their structure is consistent with “general” teleost ovarian anatomy and thus differs from Scorpaena, Helicolenus and Sebastes species whose ovaries are adapted for specialized reproductive modes. The reproductive strategy of N. pandus of maximizing the reproductive output of females, by this sex attaining a larger size than males and pair spawning (i.e., large disparity in I_GS values) demonstrates the close lineage between the Neosebastes and other Scorpaeniformes, such as the Scorpaena, Helicolenus and Sebastes.     

Sex Change in Both Directions by Alteration of Social Dominance in Trimma okinawae (Pisces: Gobiidae)

The mating system of the gobiid fish Trimma okinawae is one of polygynous hermaphroditism, in which the largest female of a social unit changes sex following the removal of the dominant male. Histological observations of the gonads however, revealed that males have an ovarian tissue within a functional testis. The occurrence of ovarian tissue in the functional male suggests that T. okinawae males should be able to revert back into being functional females. To test this prediction, we placed females in an aquarium and allowed them to change sex. After confirming sex change from female to male, we individually placed new males into another aquarium and added a larger male to each. Our experiments revealed that females change sex and become males upon the removal of dominant males, and that those males changed sex again and became females in the presence of larger males. Sex change in both directions may be advantageous when a male is forced to become subordinate following the take over of the social unit by a larger male.     

Psychobiology of sexual behavior in a whiptail lizard, Cnemidophorus inornatus

This study investigated the effects of social environment on gonadal recrudescence and sexual behavior in male and female Little Striped Whiptail lizards (Cnemidophorus inornatus). The presence of sexually active males facilitates ovarian recrudescence in conspecific females. Similarly, the presence of reproductively active females facilitates testicular recrudescence in conspecific males. Males housed with females, however, had lower average circulating concentrations of testosterone and dihydrotestosterone, and higher average concentrations of corticosterone compared to intact males housed in isolation. In other studies, the presence of reproductively active females partially restored courtship behavior in castrated males compared to castrated males housed in isolation. Despite the stimulatory effects of females on castrates, exogenous androgens are required for complete restoration of all components of sexual behavior in male C. inornatus. Females are receptive to male courtship and copulatory behavior only during the vitellogenic stages; females in previtellogenic or postovulatory ovarian stages aggressively reject male courtship advances. These findings demonstrate reciprocal effects of sexual behaviors of males and females upon each other's reproductive behavior and physiology.     

Reproductive biology of Astyanax fasciatus (Pisces: Characiformes) in a reservoir in southeastern Brazil

To study the reproductive biology of Astyanax fasciatus (Cuvier, 1819) in Furnas Reservoir, Minas Gerais, Brazil, a total of 1307 specimens were captured in bimonthly sampling from August 1993 to July 1994. The sex ratio showed a predominance of females, representing 65.2% of the total sample. The stages of gonadal maturation and spawning type were determined through macro- and microscopic analysis of the gonads as well as by variation in the gonadosomatic indices. A . fasciatus showed fractionated spawning and reproduction throughout the year, with spawning peaks influenced by water temperature and rainfall. Males and females initiated gonadal maturation at a mean standard length of 6.4 and 6.5 cm, respectively. During gonadal maturation, females showed a reduction in hepatosomatic index (from 1.06 to 0.83), suggesting that hepatic substances are transferred from the liver to the ovaries. In the reproductive period, A. fasciatus had lower stomach repletion and coelomic fat indices, indicating that this species ate less and consumed more fat reserves when reproduction had the maximum GSI (11.3 for females and 2.7 for males). Weight of the ovaries had a positive influence on the condition factor (K1), as the lowest K2 value (weight without gonads) were obtained during maturation, confirming the influence of the ovaries upon the physiological condition of the females. In weight–length relationship, parameter b was 3.02 for females and 2.23 for males, and the correlation coefficient ( r ²) was 0.84 and 0.66, respectively.     

Multiple mechanisms of phenotype development in the bluehead wrasse

Despite having detailed information on mechanisms mediating sex-typical behavior in many species, we have little understanding of whether the same mechanisms regulate these behaviors when they are performed in the same species under different social contexts. In the five field experiments of this study of bluehead wrasses (Thalassoma bifasciatum), a sex-changing fish, we examined the roles of arginine vasotocin (AVT) and the potent teleost androgen 11-ketotestosterone (11KT) in mediating sexual and aggressive behaviors typical of dominant males. We demonstrated that AVT appears necessary for the assumption of dominant territorial status in males and females, but is sufficient only in the socially dominant terminal phase (TP) male phenotype. Specifically, an AVP V(1) receptor antagonist prevented both TP males and females from gaining dominance over recently vacated territories. However, unlike TP males in a previous study, neither females nor initial phase males responded to AVT treatment with increases in display of TP male typical behaviors when under social conditions that inhibit sex change. Treating females with 11KT did not alter responsiveness to AVT, but did induce male coloration and courtship behavior that was not observed in oil-treated females. Combined with the results of a previous study, these results indicate that the ability of AVT to induce male-typical behavior differs among sexual phenotypes and that this differential responsiveness appears to be dependent on social context and not directly on exposure to 11KT. Furthermore, since 11KT can induce courtship behavior in females that is not affected by AVT, there may be different hormonal mechanisms mediating courtship behavior under different social contexts.     

Steroid hormone profiles and correlative gonadal histological changes during natural sex reversal of sobaity kept in tanks and sea-cages

The gonadosomatic index of sobaity Sparidentex hasta fits well with the natural spawning season of February-March. At 12 and 24 months all the population matured as males. However, during this time, between April-September intersex gonads were seen. From October of the third year of life, females were seen for the first time. These changes in the histology of the gonads were correlated with the hormonal profile. Testosterone showed no significant correlation with sex but 11-ketotestosterone correlated very well with the mature male gonads and thus can be used for sexing. Oestradiol-17β higher in sex reversed individuals (females) in the spawning season than in males. The sequence of events in the protandrous sex change of this fish during the first two spawning seasons is male → intersex → male. However, during the third spawning season (age 36–37 months) this sequence is male →intersex → male or female (10–17%).     

The multiple spawning pattern of weakfish in the Chesapeake Bay and Middle Atlantic Bight

Weakfish Cynoscion regalis were collected from commercial fisheries in the Chesapeake Bay and the Middle Atlantic Bight (n=4380) during 1989–1992 and their reproductive biology assessed using the gonadosomatic index, macroscopic gonad stages, oocyte diameter distributions, microscopic whole oocyte analysis and histology. Sex ratios were approximately 3:1, females to males, in 1990–1992. Most fish (90%) attained sexual maturity by age 1 and at a small size. Estimated mean length at first maturity was: 164mm total length (TL) for males, and 170 mm TL for females. Weakfish spawn within the Chesapeake Bay, as far north as the Virginia/ Maryland border. Although spawning occurred during May–August and gonad development and initiation of spawning was synchronous, cessation of spawning was asynchronous. There was no indication that older fish exhibited a more extended spawning season than younger fish. Weakfish are multiple spawners with indeterminate fecundity. Oocyte development is asynchronous with oocytes of all stages being present in developed ovaries. Because of the complex and dynamic weakfish ovarian cycle, typical methods of assessing reproduction, such as the GSI and macroscopic gonad stages, are inadequate for this species if not used in conjunction with more detailed methods such as histology.     

Gonadal restructuring and correlative steroid hormone profiles during natural sex change in protogynous honeycomb grouper (Epinephelus merra)

The honeycomb grouper shows protogynous hermaphroditism. The endocrine mechanisms involved in gonadal restructuring throughout protogynous sex change are largely unknown. In the present study, we investigated changes in the gonadal structures and levels of serum sex steroid hormones during female to male sex change in the honeycomb grouper. On the basis of histological changes, entire process of sex change was assigned into four developmental phases: female, early transition (ET), late transition (LT), and male phase. At the female phase, the oocytes of several developmental stages were observed including gonial germ cells in the periphery of ovigerous lamellae. At the beginning of ET phase, perinucleolar and previtellogenic oocytes began degenerating, followed by proliferation of spermatogonia toward the center of lamella. The LT phase was characterized by further degeneration of oocytes and rapid proliferation of spermatogenic germ cells throughout the gonad. At the male phase, no ovarian cells were observed and testis had germ cells undergoing active spermatogenesis. Serum levels of estradiol-17beta (E2) were high in females in the breeding season, but low in the non-breeding female, transitional and male phase, and those of 11-ketotestosterone (11-KT) and testosterone (T) were low in females and gradually increased in the transitional and male phase. The present results suggest that low serum E2 levels and degeneration of oocytes accompanied by concomitant increase in the 11-KT levels and proliferation of spermatogenic germ cells are probably the events mediating protogynous sex change in the honeycomb grouper.