Endocrine changes associated with spawning behavior and social stimuli in a wild population of rainbow trout (Salmo gairdneri). I. Males

Reproduction and Maturation of Sea Bass, Lateolabrax japonicus, after Transportation from Net-Cages to Indoor Tanks

To determine whether the reproductive processes of sea bass, Lateolabrax japonicus, proceed normally after transportation from an outdoor net-cage into indoor tanks, we examined changes in the gonadosomatic index (GSI), histological gonadal tissue, and plasma levels of sex hormones (testosterone and estradiol-17ß) during their annual reproductive cycle. We also measured maturation and spawning across two sea water salinity levels (full and low salinity). Fecundity was estimated by the relationship between egg number and body size in female sea bass. Monthly changes in the GSI, histological gonadal tissues, and oocyte size showed both male and female sea bass reach final maturation in January and February, respectively, indicating that the spermiation of males occurs earlier than the spawning of females. The histological results indicated that the sea bass is a multiple spawner, similar to many marine teleosts, exhibiting group-synchronous oocyte development. Female maturation and spawning were enhanced in lower salinity seawater (29.6–31.0 psu) compared to that of normal salinity (34.5–35.1 psu). These results confirm that sea bass reproduction can occur successfully in captivity and imply that fertilized eggs can be collected from February to March. Additionally, our results show that lower salinity enhances oocyte maturation and spawning of female sea bass.

Gonadal steroid fluctuations and reproduction results of European grayling (Thymallus thymallus L.) from broodstock farmed in a recirculation aquaculture system

The initial experiment of this study was conducted to determine whether sex steroid concentrations varied before, during and after the reproductive season of European grayling (Thymallus thymallus L.) farmed broodstock confined in a recirculation aquaculture system (RAS). The results indicated that the plasma sex steroid (testosterone - T, progesterone - P₄ and estradiol - E₂) concentrations varied (P < 0.05) during these reproductive periods. There were greater concentrations of T, P₄ and E₂ before and during the grayling reproductive season indicating there are important functions of these steroid hormones associated with gonadal maturation, gamete production and reproductive behavior during the spawning period. In the second experiment of this study, the effectiveness of European grayling controlled reproduction treatment regimens was analyzed and there were 34.69 % and 68.18 % having ovulations in the 2 and 3-year-old broodfish, respectively. Of the embryos developing to the eyed-egg stage, there were 3.70 % and 6.87 % derived from eggs of 2- and 3-year-old grayling females, respectively. Proportions of embryos developing from the eyed-egg stage to hatching were 38.1 % and 52.1 % from eggs of 2- and 3-year-old grayling females, respectively, when there was culturing in a RAS. The results indicate that with grayling broodfish there is greater efficacy in induction of reproduction when there is imposing of the controlled reproduction treatment regimen on 3- rather than 2-year-old broodfish.

Exploring the Impact of a Low-Protein High-Carbohydrate Diet in Mature Broodstock of a Glucose-Intolerant Teleost, the Rainbow Trout

Sustainable aquaculture production requires a greater reduction in the use of marine-derived ingredients, and one of the most promising solutions today is the augmentation in the proportion of digestible carbohydrates in aquafeed. This challenge is particularly difficult for high trophic level teleost fish as they are considered to be glucose-intolerant (growth delay and persistent postprandial hyperglycemia observed in juveniles fed a diet containing more than 20% of carbohydrates). It was previously suggested that broodstock could potentially use carbohydrates more efficiently than juveniles, probably due to important metabolic changes that occur during gametogenesis. To investigate this hypothesis, 2-year old male and female rainbow trout (Oncorhynchus mykiss) were either fed a diet containing no carbohydrates (NC) or a 35%-carbohydrate diet (HC) for an entire reproductive cycle. Zootechnical parameters as well as the activities of enzymes involved in carbohydrate metabolism were measured in livers and gonads. Fish were then reproduced to investigate the effects of such a diet on reproductive performance. Broodstock consumed the HC diet, and in contrast to what is commonly observed in juveniles, they were able to grow normally and they did not display postprandial hyperglycemia. The modulation of their hepatic metabolism, with an augmentation of the glycogenesis, the pentose phosphate pathway and a possible better regulation of gluconeogenesis, may explain their improved ability to use dietary carbohydrates. Although the HC diet did induce precocious maturation, the reproductive performance of fish was not affected, confirming that broodstock are able to reproduce when fed a low-protein high-carbohydrate diet. In conclusion, this exploratory work has shown that broodstock are able to use a diet containing digestible carbohydrates as high as 35% and can then grow and reproduce normally over an entire reproductive cycle for females and at least at the beginning of the cycle for males. These results are highly promising and suggest that dietary carbohydrates can at least partially replace proteins in broodstock aquafeed.

Rapid sex steroid effects on reproductive responses in male goldfish: Sensory and motor mechanisms

Contribution to Special Issue on Fast effects of steroids. Although we have learned a great deal about the molecular mechanisms through which sex steroids rapidly affect cellular physiology, we still know little about the links between those mechanisms and behavioral output, nor about their functional consequences in natural contexts. In this review, we first briefly discuss the contexts associated with rapid effects of sex steroids on reproductive behaviors and their likely functional outcomes, as well the sensory, motor, and motivational mechanisms associated with those effects. We then discuss our recent studies on the rapid effects of testosterone in goldfish. Those studies indicate that testosterone, through its aromatization and the subsequent activation of estrogen receptors, rapidly stimulates physiological processes related to the release of milt/sperm through likely influences on motor pathways, as well as behavioral responses to female visual stimuli that may reflect, in part, influences on early stages of sensory processing. Such motor and sensory mechanism are likely important for sperm competition and mate detection / tracking, respectively, in competitive mating contexts. We also present preliminary data on rapid effects of testosterone on responses to pheromones that may not involve estrogen receptors, suggesting a dissociation in the receptor mechanisms that mediate behavioral responses in different sensory modalities. Lastly, we briefly discuss the implications of our work on unresolved questions about rapid sex steroid neuromodulation in fish.

Zygoparity and sex steroid hormone profiles in bluemouth Helicolenus dactylopterus

Two hundred and seven individuals (103 females and 104 males) of bluemouth Helicolenus dactylopterus (Scorpaeniformes, Sebastidae), a commercially important deep-water species with an unusual reproductive strategy, from the eastern Atlantic Ocean ranging from 13·9 to 37·5 cm total length (L_T ) were analysed from September 2011 to October 2012. The analysis included gonad maturity phases and blood-plasma levels of oestradiol-17β (E₂ ), 11-ketotestosterone (11-KT) and 17,20β-dihydroxypregn-4-en-3-one (17,20β-P). Results confirmed the existence of an annual reproductive cycle with asynchrony between females and males and a spawning season from January to May. A pronounced peak in 17,20β-P in October for both sexes was associated with possible mating behaviour and recent copula. Levels of E₂ increased preceding the elevation of the gonado-somatic index during ovarian growth and were lower during regression and regeneration. The frequency distribution of oocyte-embryonic stages and variation of hormone levels suggest the existence of daily rhythms. Fertilization was detected between 2000-0000 and 0800-1200 h and spawning took place throughout the day peaking between 2000 and 0000 h. The cyclic pattern of sex steroids and ovarian recruitment provides a new insight into the reproductive strategy of this species.

Effects of temperature on the final stages of sexual maturation in Atlantic salmon (Salmo salar L.)

Maturing male and female Atlantic salmon (Salmo salar L.) were held under three temperature regimes for 10 weeks between September and December: warm (constant 14-16 °C), ambient (decreasing from 11 to 5 °C), and cold (decreasing from 7 to 3 °C). Blood samples were analyzed for plasma steroid levels, and the fish were inspected for the presence of expressible milt (total volume and spermatocrit) and ovulation weekly. Samples of eggs were dry-fertilized with milt stripped from three males held at the same temperatures and incubated until the eyed stage. In females, levels of plasma testosterone (T) and 17β-oestradiol (E2) dropped as ovulation approached, concurrent with a rapid increase in levels of plasma 17α,20β-dihydroxy-4-pregnen-3-one (17,20β-P). In males, levels of T and 11-ketotestosterone (11-KT) peaked 2-3 weeks after the first appearance of expressible milt, while levels of 17,20β-P increased steadily and did not exhibit a definite peak. Exposure of females to cold water amplified and advanced the profiles of all three steroids compared with the ambient group, and increased the survival rates to the eyed egg stage. Cold water had no immediate effect on the male steroid profiles, but later, higher levels of 17,20β-P were evident compared with both the ambient controls and the warm water group, while the effects on 11-KT and T were more variable. Exposure to warm water completely inhibited both milt production and ovulation. Moreover, warm water modulated the steroid profiles of the males with lower 11-KT levels compared with ambient controls and lower 17,20β-P level compared with cold-water-treated males. In females, warm water resulted in total inhibition of the peri-ovulatory peak in 17,20β-P and prevented the normal decline of T and E2 levels associated with ovulation. The findings of the present study are highly relevant for broodstock management in aquaculture, as well in understanding the impact of climate change/temperature variability on wild salmon spawning.

A multidisciplinary study on social status and the relationship between inter-individual variation in hormone levels and agonistic behavior in a Neotropical cichlid fish

Social animals with hierarchal dominance systems are particularly susceptible to their social environment. There, interactions with conspecifics and hierarchal position can greatly affect an individual's behavior, physiology and reproductive success. Our experimental model, Cichlasoma dimerus, is a serially-monogamous Neotropical cichlid fish with a hierarchical social system, established and sustained through agonistic interactions. In this work, we aimed to describe C. dimerus social structure and its association with hormonal profiles and testicular cellular composition. We recorded and quantified agonistic interactions from the territorial pair, i.e. the top ranked male and female, and the lowest ranked male of stable social groups. Plasma levels of 11-ketotestosterone (11-KT), testosterone, 17β-estradiol (E2) and cortisol were measured by ELISA. Results show that territorial pairs cooperatively guarded the territory, but rarely attacked in synchrony. Territorial males had higher testosterone and 11-KT plasma levels than non-territorial males, while E2 and an index of its metabolization from testosterone were higher in non-territorial males. No difference was observed in cortisol levels. Plasma 11-KT and an index of the conversion of testosterone to 11-KT, positively correlated with the frequency of aggressiveness, while E2 showed the opposite pattern. Territorial males had a higher gonadosomatic index than non-territorial males. The quantification of testicular cellular types revealed that the percentage of spermatocytes and spermatids was higher in non-territorial males, while territorial males showed a greater percentage of spermatozoa. Thus, C. dimerus male social position within a stable hierarchy is associated with distinct behaviors, steroid levels and testicular degree of development.

Androgens directly stimulate spermatogonial differentiation in juvenile Atlantic salmon (Salmo salar)

We studied the effects of androgens on early stages of spermatogenesis along with androgen receptor binding characteristics and the expression of selected testicular and pituitary genes. To this end, immature Atlantic salmon postsmolts received testosterone (T), adrenosterone (OA, which is converted in vivo into 11-ketotestosterone, 11-KT) or a combination of the two androgens (T+OA). Treatment with OA and T elevated the plasma levels of 11-KT and T, respectively, and co-injection of OA with T lead to high 11-KT levels but prevented plasma T levels to reach the levels observed after injecting T alone. Clear stimulatory effects were recorded as regards pituitary lhb and gnrhr4 transcript levels in fish receiving T, and to a lesser extent in fish receiving OA (but for the lhb transcript only). The two androgen receptors (Ara1 and Ara2) we cloned bound T and 11-KT and responded to these androgens in a similar way. Both androgens down-regulated testicular amh and increased igf3 transcript levels after 1 week of treatment, but effects on growth factor gene expression required sustained androgen stimulation and faded out in the groups with the decreasing T plasma levels. In fish exhibiting a sustained elevation of 11-KT plasma levels (OA and T+OA groups) for 2 weeks, the number of differentiating spermatogonia had increased while the number of undifferentiated spermatogonia decreased. Previous work showed that circulating gonadotropin levels did not increase following androgen treatments of gonad-intact immature male salmonids. Taken together, androgen treatment of immature males modulated testicular growth factor expression that, when sustained for 2 weeks, stimulated differentiation, but not self-renewal, of undifferentiated type A spermatogonia.

Differential responses of brain, gonad and muscle steroid levels to changes in social status and sex in a sequential and bidirectional hermaphroditic fish

Sex steroids can both modulate and be modulated by behavior, and their actions are mediated by complex interactions among multiple hormone sources and targets. While gonadal steroids delivered via circulation can affect behavior, changes in local brain steroid synthesis also can modulate behavior. The relative steroid load across different tissues and the association of these levels with rates of behavior have not been well studied. The bluebanded goby (Lythrypnus dalli) is a sex changing fish in which social status determines sexual phenotype. We examined changes in steroid levels in brain, gonad and body muscle at either 24 hours or 6 days after social induction of protogynous sex change, and from individuals in stable social groups not undergoing sex change. For each tissue, we measured levels of estradiol (E(2)), testosterone (T) and 11-ketotestosterone (KT). Females had more T than males in the gonads, and more E(2) in all tissues but there was no sex difference in KT. For both sexes, E(2) was higher in the gonad than in other tissues while androgens were higher in the brain. During sex change, brain T levels dropped while brain KT increased, and brain E(2) levels did not change. We found a positive relationship between androgens and aggression in the most dominant females but only when the male was removed from the social group. The results demonstrate that steroid levels are responsive to changes in the social environment, and that their concentrations vary in different tissues. Also, we suggest that rapid changes in brain androgen levels might be important in inducing behavioral and/or morphological changes associated with protogynous sex change.

The role of the maturation-inducing steroid, 17,20beta-dihydroxypregn-4-en-3-one, in male fishes: a review

The major progestin in teleosts is not progesterone, as in tetrapods, but 17,20beta-dihydroxypregn-4-en-3-one (17,20beta-P) or, in certain species, 17,20beta,21-trihydroxy-pregn-4-en-3-one (17,20beta,21-P). Several functions for 17,20beta-P and 17,20beta,21-P have been proposed (and in some cases proved). These include induction of oocyte final maturation and spermiation (milt production), enhancement of sperm motility (by alteration of the pH and fluidity of the seminal fluid) and acting as a pheromone in male cyprinids. Another important function, initiation of meiosis (the first step in both spermatogenesis and oogenesis), has only very recently been proposed. This is a process that takes place at puberty in all fishes and once a year in repeat spawners. The present review critically examines the evidence to support the proposed functions of 17,20beta-P in males, including listing of the evidence for the presence of 17,20beta-P in the blood plasma of male fishes and discussion of why, in many species, it appears to be absent (or present at low and, in some cases, unvarying concentrations); consideration of the evidence, obtained mainly from in vitro studies, for this steroid being predominantly produced by the testis, for its production being under the control of luteinizing hormone (gonadotrophin II) and, at least in salmonids, for two cell types (Leydig cells and sperm cells) being involved in its synthesis; discussion of the factors involved in the regulation of the switch from androgen to 17,20beta-P production that seems to occur in many species just at the time of spermiation; discussion of the effects of in vivo injection and application of 17,20beta-P (and closely related compounds) in males; a listing of previously published evidence that supports the proposed new function of 17,20beta-P as an initiator of meiosis; finally, discussion of the evidence for environmental endocrine disruption by progestins in fishes.

Ca(2+)-Calmodulin regulation of testicular androgen production in Mozambique tilapia (Oreochromis mossambicus)

The Ca(2+)-Calmodulin (CaM) signaling pathway has previously been shown to be involved in the regulation of teleost fish ovarian steroidogenesis. However, a putative role of CaM in testicular steroidogenesis and potential targets has not been examined. To examine whether basal steroidogenesis is modulated by Ca(2+) and CaM levels in the testis of Mozambique tilapia (Oreochromis mossambicus) we have incubated testicular fragments in vitro under different conditions and analyzed steroid output. Calcium-free medium with or without EGTA did not affect testicular basal 11-ketotestosterone (11-KT) and testosterone (T) secretion. However, addition of 80microM the CaM inhibitor W7 significantly reduced basal 11-KT, T and androstenedione secretion. Interestingly, the decreased androgen production by 80microM of W7 was accompanied by increased 11-desoxicortisol output and by the activation of cortisol synthesis in the testis, the latter undetected in untreated tissues. However, production of 17,20alpha-dihydroxy-4-pregnen-3-one was unaltered by W7. This suggests that C17,20 desmolase, 21-hydroxylase and possibly 11beta-hydroxysteroid dehydrogenase are targets for CaM. In addition, androgen production was also found to be regulated by the level of cAMP since incubations with forskolin (FK) significantly increased 11-KT and T output. A cross-talk between the cAMP and Ca(2+)-CaM signaling pathways was detected since W7 administration also decreased FK stimulated androgen production. Altogether, these data show that both basal and cAMP stimulated androgen levels were modulated by intracellular Ca(2+)-dependent CaM and that possibly Ca(2+)-CaM determines the shift in steroidogenesis from C21 steroids to androgens.

From social behavior to neural circuitry: steroid hormones rapidly modulate advertisement calling via a vocal pattern generator

Across vertebrates, androgens are rapidly elevated within minutes in response to aggressive or reproductive stimuli, yet it is unclear what the causal relationship is between fast androgen elevation and the ongoing (minute-by-minute) expression of behavior. This study tested the hypothesis that rapid increases in plasma steroid levels induce similarly rapid increases in both vocal behavior and the neurophysiological output of a central pattern generator that governs vocal behavior. In Gulf toadfish (Opsanus beta), males call to attract females to their nesting sites, and both males and females vocalize in aggressive interactions. Previous field experiments with males showed that simulated territorial challenges produce rapid and concurrent elevations in ongoing calling behavior and circulating levels of the teleost-specific androgen 11-ketotestosterone (11kT), but not the glucocorticoid cortisol. The current field experiments showed that non-invasive (food) delivery of 11kT, but not cortisol, induced an elevation within 10 min in the ongoing calling behavior of males. Electrophysiological experiments revealed that intramuscular injections of either 11kT or cortisol, but neither testosterone nor 17-beta-estradiol, induced increases within 5 min in the output of the vocal pattern generator in males, whereas only cortisol had similarly fast effects in females. The field behavioral results support predictions generated by the challenge hypothesis and also parallel the 11kT-dependent modulation of the vocal pattern generator in males. The cortisol effect on the vocal pattern generator in both sexes predicts that glucocorticoids regulate vocalizations in non-advertisement contexts. Together, these experiments provide strong support for the hypothesis that surges in circulating steroid levels play a causal role in shaping rapid changes in social behavior (vocalizations) through non-genomic-like actions on neural (vocal motor) circuits that directly encode behavioral patterning.

Raffles, roles, and the outcome of sperm competition in sockeye salmon

In species with male alternative reproductive phenotypes, one phenotype is usually disadvantaged in mating competition. In salmonid fishes, large late-maturing males pair with nesting females and maintain close contact before and during spawning. Small early-maturing males have little contact with nesting females and, during spawning, begin to release sperm after the paired male. The effects of male phenotype and timing of ejaculation on success in sperm competition are not known. In this study, we determined paternity of offspring resulting from in vitro competitive fertilizations to examine these two aspects of sperm competition in sockeye salmon, Oncorhynchus nerka (Walbaum, 1792). When we fertilized eggs with mixtures of equal numbers of sperm from each of two male age classes, we found that success in sperm competition did not depend on male age. However, success in these competitive fertilizations did not conform to the fair raffle model of sperm competition, since paternity in most of the clutches was biased in favour of one male. When we added milt from two males sequentially to a batch of eggs, we found that sperm from the second male fertilized fewer eggs than sperm from the first male, but the difference was less than expected. In addition, a male's success when his milt was added first was not correlated with his success when his milt was added second.

Social modulation of androgen levels in male teleost fish

Androgens are classically thought of as the sex steroids controlling male reproduction. However, in recent years evidence has accumulated showing that androgens can also be affected by the interactions between conspecifics, suggesting reciprocal interactions between androgens and behaviour. These results have been interpreted as an adaptation for individuals to adjust their agonistic motivation and to cope with changes in their social environment. Thus, male-male interactions would stimulate the production of androgens, and the levels of androgens would be a function of the stability of its social environment ['challenge hypothesis', Gen. Comp. Endocrinol. 56 (1984) 417]. Here the available data on social modulation of androgen levels in male teleosts are reviewed and some predictions of the challenge hypothesis are addressed using teleosts as a study model. We investigate the causal link between social status, territoriality and elevated androgen levels and the available evidence suggests that the social environment indeed modulates the endocrine axis of teleosts. The association between higher androgen levels and social rank emerges mainly in periods of social instability. As reported in the avian literature, in teleosts the trade-off between androgens and parental care is indicated by the fact that during the parental phase breeding males decreased their androgen levels. A comparison of androgen responsiveness between teleost species with different mating and parenting systems also reveals that parenting explains the variation observed in androgen responsiveness to a higher degree than the mating strategy. Finally, the adaptive value of social modulation of androgens and some of its evolutionary consequences are discussed.

Involvement of sex steroid hormones in the early stages of spermatogenesis in Japanese huchen (Hucho perryi )

In higher vertebrates, considerable progress has been made in understanding the endocrine regulation of puberty; however, in teleosts, the regulatory mechanisms of spermatogenesis during the first annual cycle remain unclear. The present study was conducted to understand the regulatory mechanisms of spermatogenesis throughout the different stages of the first spermatogenic cycle and to check the ability of various steroids and hormones to induce in vitro spermatogonial proliferation in Japanese huchen (Hucho perryi ). The results indicate that the serum level of 11-ketotestosterone (11-KT) was positively associated with germ cell type; the level first began to rise with the appearance of late-type B spermatogonia and continued to increase gradually throughout the active spermatogenic stages and spermiogenesis, reaching a peak value 2 wk before spawning, and then declined. During the spermatogenic stages, the serum concentration of 17alpha,20beta-dihydroxy-4-pregnen-3-one (17alpha,20beta-DP) was undetectable. Only a small peak was detected with the appearance of spermatocytes and spermatids, and at the time of spawning, the level increased dramatically, reaching its maximum value with the onset of milt production. Despite the high variation in serum levels of 17beta-estradiol (E2) both between months and among the individuals, E2 was found during the whole reproductive cycle. From these results, we concluded that 1) 11-KT is necessary for the initiation of spermatogenesis and sperm production, and it probably plays a role in spermiation, 2) 17alpha,20beta-DP is essential for the final maturation stage, could play a significant role in the mitosis phase and meiosis process, and probably participates in the regulation of spawning behavior, and 3) estrogen is an indispensable male hormone that plays a physiological role in some aspects of testicular functions, especially during the mitotic phase. The three steroids were also able to induce DNA synthesis, spermatogonial renewal, and/or spermatogonial proliferation in vitro.

Sex steroids relative to alternative mating behaviors in the simultaneous hermaphrodite Serranus subligarius (Perciformes: Serranidae)

This study is the first investigation of reproductive endocrinology in a simultaneously hermaphroditic teleost, the belted sandfish (Serranus subligarius). We address two questions: (1) Do steroid hormone levels vary during the spawning season or during the daily spawning cycle of sandfish? (2) Do hormone levels vary relative to an individual's phenotype-size, frequency of spawning and aggressive behaviors, and proportion of testis in the gonad? We analyzed circulating estradiol-17beta (E2), testosterone (T), 11-ketotestosterone (11KT), 17alpha,20beta,21-trihydroxy-4-pregnen-3-one (20betaS), and 17alpha,20beta-dihydroxy-4-pregnen-3-one (DHP) concentrations in a field population. Only E2 levels were significantly higher at the new and full moon, suggesting peak periods of vitellogenesis at these times. Naturally spawning sandfish were sampled every 2 h during the photophase of a 25-h period (12 pm to 1 pm the following day) and gonadosomatic index, degree of oocyte hydration and ovulation, and plasma levels of E2, T, DHP, and 20betaS were analyzed. E2 and T levels did not vary during photophase, suggesting continuous recruitment of oocytes into vitellogenesis. The 20betaS levels peaked around the time of final oocyte maturation. Since frequency of spawning behaviors changes with body size, we captured individuals of various sizes throughout the spawning season and analyzed circulating levels of hormones. 11KT and 20betaS levels increased significantly with body size. In 1992, we quantified frequency of spawning and aggressive behaviors, circulating T and 11KT levels and testicular mass relative to ovotestis mass in focal animals. 11KT levels tended to be positively correlated with frequency of courting male behavior, but were unrelated to the frequency of aggressive behavior or testis mass. Because hormone levels increased with size and frequency of each spawning behavior changes with size, we propose that sex steroids influence growth-related changes in spawning tactics of individuals.

Reproductive condition and behavior in relation to plasma levels of gonadal steroids in the spiny damselfish Acanthochromis polyacanthus

Gonadal condition and plasma levels of gonadal steroids were measured in relation to behavior in the biparental brood-protecting spiny damselfish Acanthochromis polyacanthus. Fish were captured by SCUBA divers from natural populations on Australia's Great Barrier Reef and immediately bled underwater, following diver or video observation of precapture behaviour. In winter (July), most fish were nonterritorial, with a low proportion of mature males, or vitellogenic females present. In spring (November), most fish were territorial with broods of young at varying stages of maturity, and all stages of gonadal development were represented. Territorial males were larger than nonterritorial fish, but territorial fish that had large (older) young (the end of the brooding phase) had lower condition factors than fish at other stages. Males of all gonad stages had a high proportion of spermatozoa in the testis, but this was higher in November than in July. Ovaries of females commonly had several classes of developing follicles present, although fish that were brooding large young had regressed ovaries with a high incidence of atresia. Plasma levels of testosterone (T) and 11-ketotestosterone were elevated in males of advanced gonadal maturity, and also in relation to recent or imminent spawning behaviour, but there were no changes in plasma 17, 20beta-dihydroxy-4-pregnen-3-one (17,20betaP), which was near assay detection limits at all times. Females had elevated T and 17beta-estradiol (E2) in association with vitellogenesis and elevated T in relation to spawning activity in some fish, but as in males, 17,20betaP levels were low and unchanging. Territorial females without young had lower cortisol levels than nonterritorial fish, or females protecting young. The results confirm the importance of elevated androgens to spawning activity in territorial male fish, but not females where endocrine activity is more closely related to stage of ovarian development. Extended brooding appears to inhibit vitellogenesis, perhaps via a stress-related mechanism.

Reproductive behavioural sequences of single pairs of Atlantic salmon in an experimental stream

We studied 12 size-matched pairs of Atlantic salmon, Salmo salar, in an experimental stream in southwest France, to determine whether fish activity and motivation changed during the course of reproduction. The absolute weight of spawners did not affect their spawning activity. On average, females deposited their eggs within 3 days in nine nests. Male and female breeding behaviours changed throughout the reproductive period. This cyclic variation in behaviour appeared to be determined in part by the activity of the other sex, as a consequence of complex interplay between the sexes, but also largely by the stage of the spawning period. During the first three ovipositions, male-female stimulus-reaction chaining became more consistent just before spawning, which may help synchronize gamete release for successful fertilization. During the last three ovipositions, sequence chaining between the sexes was less coherent, possibly as a result of reduced mate attractiveness and/or physiological limitations. Copyright 1999 The Association for the Study of Animal Behaviour.

Steroid hormones and paternal care in the plainfin midshipman fish (Porichthys notatus)

The present study investigated the relationship between plasma steroid hormone levels and the expression ofpaternal behavior in the plainfin midshipman fish (Porichthys notatus), where males may simultaneously care for multiple clutches in different stages of development. Blood samples were collected from free-living parental males during that part of the breeding season when males may be found in various stages of parental care. Plasma 11-ketotestosterone levels were significantly higher in males with empty nests and nests containing only eggs than in males with nests containing embryos. All males with nests containing embryos had undetectable testosterone levels, whereas testosterone levels were detectable in many males with empty nests or nests containing only eggs. Estradiol levels were detectable in only a few males from nests with no eggs or nests containing only eggs. Cortisol levels were not correlated with stage of paternal care or with handling time. These results follow the frequently reported vertebrate pattern of declining androgen levels over the course of the breeding season or during the period of parental care. However, many male midshipman guarding nests containing only eggs had androgen levels similar to those of males whose nests contained no offspring. Thus the pattern of androgen levels exhibited by reproductively active parental male midshipman may reflect a compromise between investment in paternal care versus courtship and/or territoriality.

Plasma testosterone and 11-ketotestosterone levels of male pacu Piaractus mesopotamicus (Cypriniformes, Characidae)

The levels of testosterone (T) and 11-ketotestosterone (11-KT) of the South American pacu Piaractus mesopotamicus were determined by radioimmunoassay during two stages of the reproductive cycle, i.e., resting and maturation, and the gonadosomatic index (GSI) was calculated. The highest levels of T and 11-KT were reached during the maturation stage (T = 2400 +/- 56 pg/ml; 11-KT = 2300 +/- 60 pg/ml) and lower levels were maintained during the resting period. The rise in androgen levels occurred with the appearance of spermatozoa in the maturation stage, when GSI was highest.

Plasma gonadotropin II, sex steroids, and thyroid hormones in wild striped bass (Morone saxatilis) during spermiation and final oocyte maturation

The blood levels of gonadotropin II (GtH II), sex-steroid hormones, and thyroid hormones were determined in wild spermiating male striped bass (Morone saxatilis) in males and in females at various stages of final oocyte maturation (FOM), captured on their spawning grounds. The progression of spermiation was associated with increases in plasma GtH II and decreases in plasma testosterone (T), 11-ketotestosterone, and thyroxine (T4). Plasma triiodothyronine (T3) remained at high and relatively unchanged levels. Plasma levels of 17,20beta-dihydroxy-4-pregnen-3-one (17,20beta-P) and 17,20beta, 21-trihydroxy-4-pregnen-3-one (17,20beta,21-P), the proposed maturation-inducing steroids (MIS) in striped bass, were low and unchanged during the same period. It was concluded that low progestogen levels are adequate to induce spermiation in striped bass, and that higher levels may be associated with spawning behavior. In the females, based on the profiles of the studied hormones, FOM was separated into two phases. Early FOM, which included germinal vesicle (GV) migration and lipid-droplet coalescence, was associated with elevations in plasma GtH II, T, and estradiol 17beta. Late FOM, which included GV breakdown and yolk-globule coalescence, was associated with a further surge in plasma GtH II, increases in the levels of the two MIS, mainly 17, 20beta-P, and a drop in T4. Plasma T3 levels did not change during FOM. Examination of conjugated steroids demonstrated, in the males, a reduction in conjugated androgens at the peak of the spawning season and, in the females, a small increase in conjugated 17, 20beta-dihydroxylated and 5beta-reduced,3alpha-hydroxylated steroids after spawning. This is the most comprehensive report, to date, on the endocrine regulation of gonadal maturation in wild striped bass, demonstrating that a two-stage process of FOM is regulated by different endocrine signals, providing further evidence for the involvement of 17,20beta-P as a MIS in the females, and indicating that both males and females are in an euthyroid state during the spawning season.

Male dominance, plasma hormone concentrations, and availability of milt in male rainbow trout (Oncorhynchus mykiss)

The relationships among social status, endocrine profile, and amounts of milt available by stripping were examined in pairs of male rainbow trout (Oncorhynchus mykiss) competing for access to sexually active females in laboratory spawning channels. Gonadotropic hormone (GtH II), the gonadal steroids 11-ketotestosterone, testosterone, and 17α,20β-dihydroxy-4-pregnen-3-one, and milt volumes increased in dominant males in response to stimuli provided by a nesting female. Subordinate males in the same location did not show endocrine or milt responses. Following the removal of the dominant male of each pair, plasma hormone and milt levels increased in the previously subordinate males. This result indicates that endocrine and spermiation responses depend upon close-range sensory and behavioural interaction with the sexually active female. Treatment with testosterone did not cause a change in behaviour or social status of smaller males predicted to be subordinate.

Endocrine and gonadal changes during the annual reproductive cycle of the freshwater teleost,Stizostedion vitreum

The annual reproductive cycle of walleye (Stizostedion vitreum) was characterized by documenting changes in gonadal development and serum levels of estradiol-17β (E2), testosterone (T), 17α,20β-dihydroxy-4-pregnen-3-one (17,20-P), and 11-ketotestosterone (11-KT) in wild fish captured from upper midwestern lakes and rivers throughout the year. Fish from the populations used in this study spawn annually in early- to mid-April. Walleye showed group synchronous ovarian development with exogenous vitellogenesis beginning in autumn. Oocyte diameters increased rapidly from ∼ 200 μm in October to ∼ 1,000 μm in November, and reached a maximum of 1,500 μm just prior to spawning. Changes in gonadosomatic indices (GSIs) paralleled changes in oocyte diameters. Serum E2 levels in females increased rapidly from low values in October (< 0.1 ng ml(-1)) to peak levels of 3.7 ng ml(-1) in November, coinciding with the period of the most rapid ovarian growth. Subsequently, E2 levels decreased from December through spawning. Serum T levels exhibited a bimodal pattern, increasing to 1.6 ng ml(-1) in November, and peaking again at 3.3 ng ml(-1) just prior to spawning. We detected 11-KT in the serum of some females at concentrations up to 5.6 ng ml(-1), but no seasonal pattern was apparent. In this study (unlike our results in a related study) 17,20-P was not detected. In males, differentiation of spermatogonia began in late August, and by January the testes were filled (> 95% of germ cells) with spermatozoa. Mature spermatozoa could be expressed from males from January through April. GSIs ranged from 0.2% (post-spawn) to 3.2% (pre-spawn). Serum T levels rose from undetectable levels in post-spawn males to 1.6 ng ml(-1) by November, remained elevated throughout the winter, and peaked at 2.8 ng ml(-1) I prior to spawning. Levels of 11-KT in males remained low (< 10 ng ml(-1), from post-spawning through January, then increased significantly by March and peaked just prior to spawning at 39.7 ng ml(-1). Our results indicate that vitellogenesis and spermatogenesis are complete or nearly so, in walleye by early winter, and suggest that it may be possible to induce spawning in this species several months prior to the normal spawning season by subjecting fish to relatively simple environmental and hormonal treatments.

Effect of salmon gonadotropic hormone on sex steroids in male rainbow trout: plasma levels and testicular secretion in vitro

Male rainbow trout were treated with salmon gonadotropic hormone (GTH) at different stages of the circannual reproductive cycle; spawning fish were also treated with an antiserum against salmon GTH. Injection of GTH led to a several-fold increase of plasma sex steroid levels during spermatogenesis and in the spawning season but was without effect at early stages of testicular development. GTH neutralization during the spawning season was followed by a several-fold decrease of plasma sex steroid levels. During spermatogenesis and in the spawning season, both treatment regimes resulted in an increased sensitivity of testicular explants in response to a subsequent stimulation of steroid secretion in vitro. This up-regulatory response may facilitate and maintain the high sex steroid plasma levels observed during the spawning season. It may also be necessary to allow for concomitant peak values of plasma GTH and sex steroids in the spawning season, a situation difficult to understand within the negative feedback concept. The adaptive capacities of the testicular steroidogenic system indicate that it is not only an effector site for GTH but also an active part of the endocrine system controling reproduction.

Changes in plasma thyroxine, estradiol-17 beta, and 17 alpha,20 beta-dihydroxy-4-pregnen-3-one during smoltification of coho salmon

Circulating levels of plasma estradiol, 17 alpha,20 beta-dihydroxy-4-pregnen-3-one (17 alpha,20 beta PROG), and thyroxine were measured during smoltification of coho salmon in two successive years (1984 and 1985). Two elevations of thyroxine occurred in both years, the first occurred in April followed by a second increase in May. Estradiol levels were dynamic with variable changes particularly in postsmolts when estradiol levels were either depressed in 1984 or high in 1985. However, elevations of estradiol preceded the second elevation of thyroxine in May in both years when the salmon were undergoing the later stages of smoltification. There were no consistent changes of plasma 17 alpha,20B PROG during this period. Although, in 1984, there were significant elevations and depressions of 17 alpha,20B PROG, and in 1985, there was a major unexplained depression of 17 alpha,20B PROG on April 24. There were no sexual differences noted for plasma steroid levels in the juvenile fish. These data suggest that there are seasonal changes of estradiol coinciding with other developmental changes during smoltification.

Changes in plasma levels of gonadal steroids during spawning behaviour in territorial male demoiselles Chromis dispilus (Pisces: Pomacentridae) sampled underwater

Males of the demoiselle Chromis dispilus (a species endemic to New Zealand) were hand-netted from nest territories by scuba divers and blood sampled in situ. Reproductive condition and behaviour prior to capture were compared with plasma levels of testosterone (T) and 17 alpha,20 beta dihydroxy-4-pregnen-3-one (17,20 beta P). Spawning cycles of about 7 days, consisting of 1-2 days of spawning activity followed by 4-5 days of brooding behaviour, were observed. Plasma levels of T and 17,20 beta P were elevated (4-6 and 1-1.5 ng.ml-1, respectively) in fish that were engaged in courtship display, spawning, or guarding freshly spawned eggs. Levels of both hormones fell to less than 1 (T) and less than 0.4 ng.ml-1 (17,20 beta P) at the end of spawning episodes and remained low through the subsequent brooding period. T levels increased slightly toward the end of the brooding phase. Samples taken at 2- to 3-hr intervals during daylight hours showed similar correlation of steroid levels and activity; however, there was a marked fall in 17,20 beta P in spawning fish with the onset of shelter seeking at dusk. Values returned to high levels with the resumption of spawning the next day. Plasma steroid levels were not consistently correlated with reproductive condition (degree of spermiation). It is concluded that there is a strong correlation between plasma T and 17,20 beta P levels and the male spawning cycle, but not brooding or territorial behaviour per se.

Seasonal changes in and effect of castration/androgen replacement on the plasma levels of five androgens in the male three-spined stickleback, Gasterosteus aculeatus L

The seasonal changes in plasma levels of the androgens 11-ketotestosterone (OT), testosterone (T), 11 beta-hydroxytestosterone (OHT), 11-ketoandrostenedione (OA), and 11 beta-hydroxyandrostenedione (OHA) were measured in the male three-spined stickleback (Gasterosteus aculeatus L). OT was the dominant plasma androgen in the breeding season in summer and was the only androgen that peaked during this period. The levels of OT correlated closely with the development of male secondary sexual characters and reproductive behavior. T and OHT were low in all seasons, whereas OHA and OA displayed the highest levels in early winter. During the postbreeding period, the time of active spermatogenesis, all measured steroids were low. Castration resulted in an almost complete loss of plasma OT and reduced T, whereas OHT, OHA, and OA were not reliably influenced. Androstenedione implants in castrated fish increased plasma T and OA implants increased plasma OT, suggesting a nontesticular site of conversion.

Serum 11-ketotestosterone and testosterone concentrations associated with reproduction in male bluegill (Lepomis macrochirus: Centrarchidae)

Male bluegill (Lepomis macrochirus) display a complex reproductive behavior involving two alternative life history pathways: delay of sexual maturation to become "parentals" or precocious maturation as "cuckolders." The purpose of our study was to investigate the association of two androgens, 11-ketotestosterone (11KT) and testosterone (T), with reproduction in these two types of males. Radioimmunoassay techniques were used to measure daily levels of the two androgens in the blood serum of parental male bluegill captured during the prespawning, spawning, and nesting periods throughout the reproductive season. Dramatic changes in the levels of 11KT and T were observed among parental males during these periods. Peaks occurred at the onset of spawning activity during each breeding bout. Compared to spawning parental males, spawning cuckolder males had significantly lower serum levels of 11KT. In contrast, the serum levels of T among parental and cuckolder males were not significantly different. These findings suggest that the elevated levels of 11KT are associated with the behaviors displayed by spawning parental males. The levels of T, however, seem to be associated with the occurrence of a phenomenon common to both parental and cuckolder males, such as development of gonads and/or spermiation.

Endocrine changes during gonadal maturation and spawning in the orange roughy (Hoplostethus atlanticus Collett), a teleost from the midslope waters off New Zealand

Orange roughy were sampled at all stages of the reproductive cycle by trawling at depths of 700-1200 m off the coast of New Zealand. Blood samples were collected from live fish, and changes in plasma levels of gonadal steroids were correlated with gonadal development and spawning. Plasma androgens were low in spent and regressed fish of both sexes and increased during gametogenesis to peak early in the spawning period at 6.6 and 9.4 ng.ml-1 for males and females, respectively. Androgen levels dropped to near basal levels over successive days during the first week of spawning in both prespawning and ovulated or spermiated fish. Falls in plasma androgens were not accompanied by increasing levels of plasma 17 alpha,20 beta-dihydroxy-4-pregnen-3-one (17 alpha,20 beta P) which remained at or near assay detection limits throughout. 11-Deoxycortisol (11-DOC) was present in the plasma of both sexes but did not change in concert with reproductive development. 17 beta-Estradiol was present in low concentrations (maximum 0.9 ng.ml-1 plasma) in recrudescing females, whereas estrone was detectable but not elevated at any stage. 17 alpha-Hydroxyprogesterone was not detectable in the plasma of any fish at any time. It is suggested that neither 17 alpha,20 beta P nor 11-DOC were active as maturation-inducing steroids (MIS) in orange roughy and that androgens may act as MIS. If the recorded fall in androgens was due to synthesis of another steroid from a common precursor, then the unidentified steroid does not appear to have been involved in stimulating final gamete maturation, but may have some action in initiating spawning behavior.

Gonadotropin stimulated androgen secretion of rainbow trout (Salmo gairdneri Richardson) testis in vitro

1. The secretion of five androgens was quantified from trout testes under GTH-stimulation in vitro before and after the onset of milt production, and a general increase of basal and GTH stimulated androgen secretion was recorded during this period. 2. 11-Ketotestosterone, testosterone, and in spermiating males, 11 beta-hydroxytestosterone as well showed GTH dependent concentration increases, while androstenetrione and 11 beta-hydroxyandrostendione were found in highly variable amounts. 3. 17 beta-Hydroxyandrogen glucuronides in the medium (with the exception of testosterone) and tissue androgens were by far exceeded by the free androgens in the medium.

Endocrine changes associated with spawning behavior and social stimuli in a wild population of rainbow trout (Salmo gairdneri). II. Females

Rainbow trout (Salmo gairdneri) were collected from a natural spawning population at Pennask Lake, B.C. Blood samples taken from female trout at different stages of spawning were assayed by radioimmunoassay for gonadotropin (GtH), estradiol-17 beta (E2), androgens, including testosterone (T), and 17 alpha-hydroxy-20 beta-dihydroprogesterone (17,20-P). Plasma levels of androgen and estradiol were highest in females sampled shortly before ovulation ("green" females) and declined in ovulated and sexually active females, reaching lowest levels in postspawning fish. Concentrations of 17,20-P rose markedly in ovulated females allowed to dig nests and interact with sexually active males. Plasma GtH levels were similar in green unovulated females and ovulated fish prevented from spawning, but showed a marked increase in actively nest building ovulated fish. The results demonstrate that social stimuli affect plasma levels of 17,20-P and perhaps GtH. The functional significance of the endocrine responses to social factors is not clear, but it is suggested that increased hormone levels may contribute to an acceleration or synchronization of breeding, or be responsible for causing and maintaining more vigorous sexual activity.