Hormonal and behavioral correlates of morphological variation in an Amazonian electric fish (Sternarchogiton nattereri: Apteronotidae)

The weakly electric fish from the main channel of the Amazon river, Sternarchogiton nattereri, offers a striking case of morphological variation. Females and most males are toothless, or present only few minute teeth on the mandible, whereas some males exhibit exaggerated, spike-like teeth that project externally from the snout and chin. Androgens are known to influence the expression of sexually dimorphic traits, and might be involved in tooth emergence. In this study we assess the relationship in S. nattereri between morphological variation, 11 ketotestosterone (11-KT) and testosterone (T). We also examine relationships of morphology and androgen levels with electric organ discharge (EOD) frequency, reproductive condition, and seasonality. Our main finding is that male morph categories differed significantly in plasma concentrations of 11-KT, with toothed males showing higher levels of 11-KT than toothless males. By contrast, we did not detect statistical differences in T levels among male morph categories. Reproductive condition, as measured by gonadosomatic indexes (GSI), differed across two sample years, increased as the season progressed, and was higher in toothed males than in non-toothed males. EOD frequency was higher in toothed males than in either toothless males or females. Taken together, our findings suggest that S. nattereri male sexual characters are regulated by 11-KT levels, and that both morphology and androgens interact with reproductive condition and EOD frequency in ways that vary within and across reproductive seasons.     

Seasonal changes of serum sex steroids concentration and aromatase activity of gonad and brain in red-spotted grouper (Epinephelus akaara)

Levels of serum sex steroids (estradiol-17beta, E2; testosterone, T; 11-ketotestosterone, 11-KT) in male, female and natural sex-reversing red-spotted grouper (Epinephelus akaara), and aromatase activity of gonad and brain in both male and female were investigated throughout an annually reproductive cycle. In females, serum E2 and T peaked during vitellogenesis, but in males and natural sex-reversing fish, 11-KT, T and E2 reached peak during spermatogenesis. In addition, in females, serum 11-KT levels (monthly means: 0.32 +/- 0.03 ng/ml) which were very low did not significantly fluctuate during the annual reproductive cycle. In breeding season, females displayed higher E2 levels than males and sex-reversing fish, while males and sex-reversing fish showed higher 11-KT levels and, to a lesser extent, higher T levels than females. Furthermore, the changing pattern of sex steroids in males was similar to that in natural sex-reversing fish, and a second peak of serum androgens 11-KT and T appeared in December both in male and natural sex-reversing fish; significantly higher serum 11-KT levels were observed in natural sex-reversing fish than that in females from December to April. In females, but not in males, aromatase activity of brain and gonad demonstrated significantly seasonal changes (exhibiting a peak in breeding season); moreover, aromatase activity in females was higher than that in males. Furthermore, significantly lower aromatase activity in testis was observed in breeding season, in contrast to that in ovary. Taken together, the present findings indicated that changes of serum sex steroids levels and aromatase activity in red-spotted grouper were closely associated with sex inversion. In addition, the present results also suggested that sex inversion in red-spotted grouper peaked mainly from December to March.     

Androgen correlates of socially induced changes in the electric organ discharge waveform of a mormyrid fish

Weakly electric fish from the family Mormyridae produce pulsatile electric organ discharges (EODs) for use in communication. For many species, male EODs are seasonally longer in duration than those of females, and among males, there are also individual differences in EOD duration. While EOD elongation can be induced by the administration of exogenous androgens, androgen levels have never before been assessed under natural or seminatural conditions. By simulating the conditions occurring during the breeding season in the laboratory, we provide evidence of a sex difference in EOD duration as well as document levels of circulating androgens in males. In this study, we analyzed the nature of social influences on male EOD duration and plasma androgen levels in Brienomyrus brachyistius. Individual males, first housed with a single female and then placed into social groups consisting of three males and three females, showed status-dependent changes in EOD duration. Top-ranking males experienced a relatively large increase in EOD duration. Second-ranking males experienced a more modest increase, and low-ranking males experienced a decrease in EOD duration. These changes were paralleled by differences in circulating levels of plasma 11-ketotestosterone (11-KT), but not testosterone, suggesting that the changes in EOD duration may have been mediated by changes in plasma 11-KT levels. Thus, it appears that EOD duration is an accurate indicator of male status, which is under social and hormonal control.     

Plasma Sex Steroid Levels and Steroidogenesis in the Gonad of the Self-fertilizing Fish Rivulus marmoratus

Synopsis The mangrove killifish, Rivulus marmoratus, is the only known self-fertilizing vertebrate. This species is sexually dimorphic; sexually mature individuals are either hermaphrodite or primary and secondary males. Although the mangrove killifish has a unique reproductive strategy, there has been no study on the reproductive endocrinology of this species. Thus we investigated plasma sex steroid hormone levels and steroidogenesis in the gonads of R. marmoratus by enzyme linked immunosorbent assay (ELISA). Plasma 17β-estradiol (E2) and 11-ketotestosterone (11-KT) were detected both in hermaphrodite and in primary male. Ovarian follicles (follicle-enclosed oocytes) from hermaphrodites, which were categorized into early yolk stage and late yolk stage, and testis tissue of primary males were cultured with different concentrations of 17α-hydroxyprogesterone (OHP) or testosterone (T) for 24 h. Production of T, E2, 11-KT and 17α-20 β-dihydroxy-4-pregnen-3-one (17α,20β-P) in the medium from tissue culture were measured by ELISA. Early and late ovarian follicles of hermaphrodites and testis pieces of primary males synchronously secreted E2, 11-KT, and 17α,20β-P following incubation with OHP or T. We conclude that both hermaphrodite and primary male of the mangrove killifish secrete estrogen, androgen, and progestin synchronously.     

Annual changes in testicular development and plasma sex steroids in the captive male dojo loach <Emphasis Type="Italic">Misgurnus anguillicaudatus</Emphasis>

Testicular development in the captive male dojo loach Misgurnus anguillicaudatus was examined monthly in relation to the levels of plasma sex steroids [testosterone (T), 11-ketotestostrone (11-KT), and 17,20β-dihydroxy-4-pregnen-3-one (DHP)]. On the basis of testicular histology, the annual gonadal cycle was found to be divisible into 3 periods: the recovery and proliferation period, which mainly consists of early spermatogenic testis from August to November (reproductive phase I); the preparation period for the next spawning period, which mainly consists of late spermatogenic testis from December to April (reproductive phase II); and the mature period, characterized by a high proportion of mature testis from May to July (reproductive phase III). Individual variability in testicular development was high, and continuous spermatogenesis was observed throughout the year. High levels of plasma T, 11-KT, and DHP were observed during reproductive phase III. 11-KT began to increase in February, while T was present at low levels in reproductive phase II. These results suggest that the physiologically active season of testis development for breeding in the dojo loach is from May to July, although spermatogenesis occurs throughout the year.     

Endocrine and morphological correlates of reproduction in the draughtboard shark Cephaloscyllium laticeps (Elasmobranchii: Scyliorhinidae)

This study examined the endocrine and reproductive correlates of reproduction in 636 female and 468 male draughtboard sharks (Cephaloscyllium laticeps) captured from southeastern Australia. Females were oviparous and displayed a single external-type ovary with a maximum follicle diameter of 35 mm. Vitellogenesis commenced at a follicle diameter of 10 mm. Females showed a constant overlap between follicular recruitment, ovarian growth, and egg laying. The male reproductive tract consisted of paired testes with spermatocysts undergoing diametric development. Plasma levels of the presumptive gonadal steroids, testosterone (T), 17beta-estradiol (E2), progesterone (P4), and 11-ketotestosterone (11-KT; males only) were correlated with morphological developmental stages of the gonads. In females, E2 increased as the follicle developed before declining as the follicle reached maturity. T remained low during the first stages of ovarian growth and increased as the follicle reached maturity. P4 showed a peak just before ovulation. In males, T was the only hormone that varied with maturity, increasing in adults; E2 and P4 were present at low plasma concentrations in males and did not change with stage of gonadal development. 11-KT was undetectable at all times. Endocrine changes in draughtboard sharks were consistent with hormonal correlates reported for other species and suggest roles for E2( in females) and T (in both sexes) in gametogenesis and P4 in maturational events in females.     

Changes in hormonal profile, gonads and sperm quality of Argyrosomus regius (Pisces, Scianidae) during the first sexual differentiation and maturation

In the present study, sexual gonadal differentiation and first sexual maturation of Meagre (Argyrosomus regius) was studied, based upon the annual changes in gonadosomatic index (GSI), gonadal histology, and the plasma steroid hormones, testosterone (T), 11-ketotestosterone (11-KT), and estradiol (E2). In addition, spermatozoa characteristics were evaluated by measuring sperm motility and morphology. Results demonstrated that Meagre completes sex differentiation at 10 to 12 mo of age, and are group-synchronous spawners, which reach puberty at 2 (mean length 26.8 ± 0.7 cm, mean weight 920 ± 75 g; N = 10) and 3 (mean length 35.8 ± 0.8 cm, mean weight 1610 ± 89 g; N = 10) years of age for males and females, respectively. In males, during the sex differentiation period, T levels were significantly higher with respect to those of 11-KT; this suggests that T has a key role in the early phases of the sex differentiation. During the spawning season an increase in plasma concentrations of all hormones was observed with 11-KT levels being significantly higher that those of T. In females, during the sex differentiation period, there was an increase in E2 plasma levels, while during the first spawning season, a significant increase of T and E2 levels were measured. Regarding sperm characteristics, the measured curvilinear velocity (VCL) and straight-linear velocity (VSL), resulted in the same order of magnitude with respect to those measured in other marine fish, while the average path velocity (VAP) was similar to that measured in the European Eel. The head of Meagre spermatozoa presents as oval shaped with a surface area of approximately 3.66 μm² and a perimeter of approximately 6.65 μm. All these findings represent an important basis for further investigation on the reproductive biology of this specie and may assist the farmers to improve seed production in aquaculture.     

Testosterone and 11-ketotestosterone have different regulatory effects on electric communication signals of male Brachyhypopomus gauderio

The communication signals of electric fish can be dynamic, varying between the sexes on a circadian rhythm and in response to social and environmental cues. In the gymnotiform fish Brachyhypopomus gauderio waveform shape of the electric organ discharge (EOD) is regulated by steroid and peptide hormones. Furthermore, EOD amplitude and duration change on different timescales and in response to different social stimuli, suggesting that they are regulated by different mechanisms. Little is known about how androgen and peptide hormone systems interact to regulate signal waveform. We investigated the relationship between the androgens testosterone (T) and 11-ketotestosterone (11-KT), the melanocortin peptide hormone α-MSH, and their roles in regulating EOD waveform of male B. gauderio. Males were implanted with androgen (T, 11-KT, or blank), and injected with α-MSH before and at the peak of androgen effect. We compared the effects of androgen implants and social interactions by giving males a size-matched male stimulus with which they could interact electrically. Social stimuli and both androgens increased EOD duration, but only social stimuli and 11-KT elevated amplitude. However, no androgen enhanced EOD amplitude to the extent of a social stimulus, suggesting that a yet unidentified hormonal pathway regulates this signal parameter. Additionally, both androgens increased response of EOD duration to α-MSH, but only 11-KT increased response of EOD amplitude to α-MSH. Social stimuli had no effect on EOD response to α-MSH. The finding that EOD amplitude is preferentially regulated by 11-KT in B. gauderio may provide the basis for independent control of amplitude and duration.     

Photoperiod and water temperature regulation of seasonal reproduction in male round stingrays (Urobatis halleri)

This study characterizes the seasonal reproductive cycle of male round stingrays (Urobatis halleri) in Seal Beach, California. Mature round stingrays were collected monthly by beach seine near the San Gabriel River outfall from August 2004–September 2006, and rays were assessed for gametogenesis and steroid hormone levels. Male round stingrays exhibit a seasonal pattern of increased gonadosomatic index (GSI), spermatogenesis, and production of testosterone (T) and 11-ketotestosterone (11-KT). Based on GSI, the male reproductive cycle was broken into three distinct phases. TUNEL positive staining was only observed in the Sertoli cells of mature spermatocysts during the degenerative testicular phase, suggesting that Sertoli cell death potentially plays a role in testicular degeneration and the regulation of sperm release. GSI, T, and 11-KT were all inversely correlated with daylength, while only T was inversely correlated with temperature. Captive male round stingrays subjected to water temperatures of 25 °C showed a significant decrease in plasma testosterone concentrations, but the same males exposed to ambient water temperatures (18 °–20 °C) exhibited T concentrations observed in wild male round stingrays during the recrudescent phase. Together, these findings suggest that temperature plays an important role in the regulation of testosterone, and may serve as an ultimate cue for reproduction in male round stingrays.     

Testosterone and estradiol potentiate the serum gonadotropin response to gonadotropin-releasing hormone in goldfish

The effects of gonadal steroids on gonadosomatic index (GSI; gonad wt/total body wt x 100), pituitary gonadotropin (GTH) content, and serum GTH response to [D-Ala6,Pro9-Net]-luteinizing hormone-releasing hormone (LHRH-A) were investigated throughout the seasonal reproductive cycle of the goldfish. Gonad-intact female fish were implanted i.p. for 5 days with silastic pellets containing no steroid (blank), testosterone (T; 100 micrograms/g), or estradiol (E2; 100 micrograms/g). The serum GTH response at 6 h following i.p. injection of saline or 0.1 microgram/g LHRH-A was assessed. In blank-implanted, saline-injected animals, seasonal variations in GSI, pituitary GTH content, and serum GTH levels were evident; maximal and minimal levels were noted in the spring and summer months, respectively. In blank-implanted fish, LHRH-A effectively stimulated GTH release in females undergoing gonadal recrudescence (late autumn and winter) and in sexually mature (spring) females, but not in sexually regressed (summer and early autumn) females. Implantation of T or E2 raised serum steroid levels to those found during ovulation in goldfish. Steroid treatments did not affect unstimulated serum GTH levels at any time of the year. Testosterone effectively potentiated the serum GTH response to LHRH-A during the entire reproductive cycle, whereas the positive effects of E2 were evident in sexually regressed and post-spawning females only. Both T and E2 potentiated the GTH response to LHRH-A in male fish. To examine the involvement of T aromatization in mediating its actions on induced GTH secretion, male and female fish were implanted with T or the nonaromatizable androgens 5 alpha-dihydroxytestosterone (DHT; 100 micrograms/g) and 11-keto-testosterone (11-KT; 250 micrograms/animal). Testosterone potentiated the GTH response to LHRH-A in both males and females whereas DHT and 11-KT were without effect. Furthermore, the positive action of T on induced GTH secretion was blocked by 2-day pretreatment with the aromatase inhibitor 1,4,6-androstatrien-3,17-dione (100 or 300 micrograms/g). Multiple i.p. injections of hCG (0.2 microgram/g every 3 days for 39 days), probably through stimulation of endogenous T secretion, resulted in potentiation of the GTH response to LHRH-A in mature male goldfish. These results clearly demonstrate that T, through aromatization to E2, can increase pituitary responsiveness to exogenous LHRH-A in gonad-intact male and female goldfish.     

Human chorionic gonadotropin-induced shifts in the electrosensory system of the weakly electric fish, Sternopygus

Sternopygus macrurus of both sexes were injected with human chorionic gonadotropin (hCG) or saline. Electric organ discharge (EOD) frequency rose after hCG injections in females and gradually declined to baseline levels over the next few weeks. EOD changes in males were more complex and variable; most males showed an initial minor rise in EOD frequency followed by a larger decrease, or simply a decrease. hCG treatment also resulted in a rise in electroreceptor best frequency and shortened electric organ pulse duration in females, and had the opposite effect on these parameters in males. The saline-injected controls showed no changes in any of these parameters. Levels of testosterone (T) and 11-ketotestosterone, but not estrogen (E), were elevated in males preceding the fall in EOD frequency, whereas neither T nor E changed significantly in females before EOD frequency increases. Saline injections caused a drop in T in the male control group and had no effect in the female control group. We presume that the effect of hCG on the electrosensory system of males is mediated via androgens. Whether the effects of hCG on females are mediated by slight increases in circulating levels of gonadal steroids, the release of hormones other than T or E, or are due to direct effects on the nervous system is not known.     

Effect of paired encounters on plasma androgens and behaviour in males and females of the spiny damselfish Acanthochromis polyacanthus

Sexually mature male and female spiny damselfish, Acanthochromis polyacanthus (Pomacentridae) were introduced to resident fish of both sexes in paired encounter trials and the effect on activity, agonistic behaviour and plasma levels of testosterone (T) and 11-ketotestosterone (11-KT) in males, and T and 17β-estradiol (E₂) in females, and cortisol in both sexes was determined. Introduced males showed suppressed levels of T in the presence of both resident males and females, whereas resident males showed elevated T in response to introduced males but not females. Plasma 11-KT levels were unchanged in either resident or introduced males. Resident males showed increased activity in the presence of males but not females. Resident females showed an increase in activity when paired with introduced females and greater aggressive behaviour towards females than males. There were no differences in plasma hormone levels in either resident or introduced female fish. Plasma cortisol levels were low in all fish and stress effects did not appear to account for differences in T levels in males. The results of the present study show that elevations in plasma T levels in resident male spiny damselfish are associated only with male presence but that suppression of T in introduced fish occurs irrespective of the sex of the resident. In contrast resident females, which show stronger evidence of aggressive behaviour do not show changes in plasma androgen levels. This suggests that aggressive behaviour in male and female fishes may be mediated by different endocrine pathways.     

Gonadal development and associated changes in liver size and sexual steroids during the reproductive cycle of captive male and female Atlantic cod (Gadus morhua L.)

Gametogenesis in female and male Atlantic cod (Gadus morhua L.) was investigated by sampling blood plasma and gonadal tissue from 19 to 33-month-old fish. The reproductive cycles of both female and male Atlantic cod are characterized by distinct annual variations in gonadal size and developmental stage and these are associated with changes in sex steroids and liver size. I(H) did not change during early gonadal development, but both spent females and males had lower I(H) than late maturing females and spermiating males, respectively. In females I(G) was correlated to plasma E2 levels and they were highest in spawning females. The lowest levels during the reproductive cycle were observed in spent females. Plasma T levels were low throughout ovarian development, and were at a minimum in spent females. 11-ketotestosterone in plasma of males increased rapidly during spermiation, while T increased at earlier testicular stages and reached maximum during spermiation. High plasma levels of steroids in male and female cod during spawning serve to promote further development and growth of less advanced stages of germ cells.     

Sex inversion of sexually immature honeycomb grouper (Epinephelus merra) by aromatase inhibitor

Previous studies have shown that estrogen plays an important role in sex change of protogynous honeycomb grouper, and that the treatments with aromatase inhibitor (AI) cause estrogen depletion and complete sex inversion of pre-spawning females into functional males. In the present study, we examined whether AI causes sex inversion of sexually immature females. Female honeycomb groupers were implanted with various doses of Fadrozole (0, 100, 500 and 1000 microg/fish) in the non-breeding season, and resultant changes in the gonadal structures and the plasma levels of sex steroid hormones (estradiol-17 beta, E2; testosterone, T; 11-ketotestosterone, 11-KT) were examined three months after implantation. Vehicle-implanted groups did not change sex, while 100 and 500 microg AI-implanted groups had turned into transitionals with intersex gonad. In contrast, the highest dose receiving group exhibited both transitional and male phases. Transitional phase gonad had atretic oocytes and spermatogenic germ cells at the late stages of spermatogenesis, while male phase testis contained spermatozoa accumulated in the seminiferous tubules. All males released sperm upon slight pressure on the abdomen. In the AI-implanted fish, plasma levels of E2 decreased in a dose-dependent manner, while the levels of 11-KT were high in the highest dose receiving group. Present results suggest that estrogen plays an important role in sex change of protogynous honeycomb grouper, and that treatments with AI potentially inhibits endogenous E2 production in vivo, causing oocyte degeneration and subsequently the sex inversion from female to male. The Fadrozole could be an important tool for manipulating the sex of hermaphrodite fishes.     

Sexual and seasonal plasticity in the emission of social electric signals. Behavioral approach and neural bases

Behavior in electric fish includes modulations of a stereotyped electric organ discharge (EOD) in addition to locomotor displays. Gymnotiformes can modulate the EOD rate to produce signals that participate in different behaviors. We studied the reproductive behavior of Brachyhypopomus pinnicaudatus both in the wild and laboratory settings. During the breeding season, fish produce sexually dimorphic social electric signals (SES): males emit three types of chirps (distinguished by their duration and internal structure), and accelerations, whereas females interrupt their EOD. Since these SES imply EOD frequency modulations, the pacemaker nucleus (PN) is involved in their generation and constitutes the main target organ to explore seasonal and sexual plasticity of the CNS. The PN has two types of neurons, pacemakers and relays, which receive modulatory inputs from pre-pacemaker structures. These neurons show an anisotropic rostro-caudal and dorso-ventral distribution that is paralleled by different field potential waveforms in distinct portions of the PN. In vivo glutamate injections in different areas of the PN provoke different kinds of EOD rate modulations. Ventral injections produce chirp-like responses in breeding males and EOD interruptions in breeding females, whereas dorsal injections provoke EOD frequency rises in both sexes. In the non-breeding season, males and females respond with interruptions when stimulated ventrally and frequency rises when injected dorsally. Our results show that changes of glutamate effects in the PN could explain the seasonal and sexual differences in the generation of SES. By means of behavioral recordings both in the wild and in laboratory settings, and by electrophysiological and pharmacological experiments, we have identified sexual and seasonal plasticity of the CNS and explored its underlying mechanisms.     

Testosterone modulates female chirping behavior in the weakly electric fish,Apteronotus leptorhynchus

The weakly electric fish, Apteronotus leptorhynchus, produces a wave-like electric organ discharge (EOD) utilized for electrolocation and communication. Both sexes communicate by emitting chirps: transient increases in EOD frequency. In males, chirping behavior and the jamming avoidance response (JAR) can be evoked by an artificial EOD stimulus delivered to the water at frequencies 1–10 Hz below the animal's own EOD. In contrast, females rarely chirp in response to this stimulus even though they show consistent JARs. To investigate whether this behavioral difference is hormone dependent, we implanted females with testosterone (T) and monitored their chirping activity over a 5 week period. Our findings indicate that elevations in blood levels of T cause an enhancement of chirping behavior and a lowering of basal EOD frequency in females. Elevated blood levels of T also appear to modulate the quality of chirps produced by hormone treated females. The effects of T on female chirping behavior and basal EOD frequency appear specific, since the magnitude of the JAR was not affected by the hormonal treatment. These findings suggest that seasonal changes in circulating concentrations of T may regulate behavioral changes in female chirping behavior and basal EOD frequency.Abbreviations DHT dihydrotestosterone - E estradiol - EOD elecdric organ discharge - GSI gonadal size index - JAR jamming avoidance response - PPn prepacemaker nucleus - T testosterone     

The involvement of sex steroid hormones in downstream and upstream migratory behavior of masu salmon

From May through July when masu salmon, Oncorhynchus masou, commence downstream migration under natural conditions, yearling precocious male masu salmon (resident form) showed higher GSI and plasma levels of testosterone (T) and 11-ketotestosterone (11-KT) in contrast to immature smolts (migratory form). From March through September coinciding with the upstream migration period, 2-year-old male and female adults also showed higher GSI and plasma levels of T, estradiol-17beta (E(2)) 11-KT, 17alpha-hydroxyprogesterone and 17alpha,20beta-dihydroxy-4-pregnene-3-one (DHP). In order to test the effects of steroid hormones on migratory behaviors, silascone tube capsules containing 500 microg of T, E(2), 11-KT, DHP, or a vehicle was implanted into smolts, castrated precocious males, or immature parr, and downstream and upstream behavior were observed in artificial raceways in spring and autumn. Downstream behavior of smolts was inhibited significantly by T, E(2) and 11-KT. Upstream behavior was stimulated by T and 11-KT in castrated precocious males and stimulated by T, E(2) and 11-KT in immature parr. These results indicate that T, E(2) and 11-KT are the factors regulating downstream and upstream migratory behavior. In particular, because of its changing patterns in plasma and significant effects, T, the common precursor hormone of E(2) (female) and 11-KT (male), is considered to play central roles in both types of behavior.     

11-ketotestosterone synchronously induces oocyte development and silvering-related changes in the Japanese eel, Anguilla japonica

To evaluate the effects of sex steroids on silvering in the Japanese eel, Anguilla japonica, the development of oocytes, eye size, digestive tract, and swim bladder were studied in relation to observations of the profiles of plasma levels of sex steroids (estradiol 17β, E2; testosterone, T; 11-ketotestosterone; 11-KT) during silvering for each sex and by administrating 11-KT to yellow eels. All steroids examined in the study increased in female eels after silvering had begun, whereas in males, only 11-KT increased significantly, and no statistical differences were found in plasma levels of E2 and T between eels in both developmental stages. 11-KT appeared to induce the early stage of oocyte growth, enlargement of the eyes, degeneration of the digestive tract and the development of the swim bladder. This suggested that 11-KT synchronously accelerates early development of the ovaries and the morphological changes, possibly in adaption to oceanic migration, and that 11-KT is one of the most important factors in early stages of development in the Japanese eel, as it appears to be in other anguillid eels.     

Effects of constant short and long photoperiod regimes on the spawning performance and sex steroid levels of female and male sea bass

Under constant short photoperiod, the spawning time of 2-year-old sea bass Dicentrarchus labrax was advanced as compared to controls, whereas spawnings were delayed under constant long photoperiod. High plasma levels of 17β-oestradiol (E_2/) and testosterone (T) in females were coincident with the appearance of vitellogenic oocytes in the ovary, while high levels of 11-ketotestosterone (11-KT) and T in males were coincident with the presence of spermiating males. Although plasma levels of E₂ in females and 11-KT in males were low during the remainder of the cycle, levels of T were always >1 ng ml⁻¹ in both sexes, suggesting that T could play an important role during the initial stages of gonadal development. The profiles of E₂ and T in females and 11-KT and T in males exposed to constant short days were similar to those in the control group, but fish which were maintained under constant long photoperiods showed a bimodal pattern of these steroids. The results obtained from fish exposed to constant photoperiod regimes provide further evidence that an endogenous process could be operating to control the reproduction of sea bass.     

Natural sex change in mature protogynous orange-spotted grouper (Epinephelus coioides): gonadal restructuring,sex hormone shifts and gene profiles

Sexual patterns of teleosts are extremely diverse and include both gonochorism and hermaphroditism. As a protogynous hermaphroditic fish, all orange-spotted groupers (Epinephelus coioides) develop directly into females, and some individuals change sex to become functional males later in life. This study investigated gonadal restructuring, shifts in sex hormone levels and gene profiles of cultured mature female groupers during the first (main) breeding season of 2019 in Huizhou, China (22° 42′ 02.6″ N, 114° 32′ 10.1″ E). Analysis of gonadal restructuring revealed that females with pre-vitellogenic ovaries underwent vitellogenesis, spawning and regression and then returned to the pre-vitellogenic stage in the late breeding season, at which point some changed sex to become males via the intersex gonad stage. A significant decrease in the level of serum 17β-estradiol (E2) was observed during ovary regression but not during sex change, whereas serum 11-ketotestosterone (11-KT) concentrations increased significantly during sex change with the highest concentration in newly developed males. Consistent with serum hormone changes, a significant decrease in cyp19a1a expression was observed during ovary regression but not during sex change, whereas the expression of cyp11c1 and hsd11b2 increased significantly during sex change. Interestingly, hsd11b2 but not cyp11c1 was significantly upregulated from the pre-vitellogenic ovary stage to the early intersex gonad stage. These results suggest that a decrease in serum E2 concentration and downregulation of cyp19a1a expression are not necessary to trigger the female-to-male transformation, whereas increased 11-KT concentration and upregulation of hsd11b2 expression may be key events for the initiation of sex change in the orange-spotted grouper.