Periovulatory female goldfish release three potential pheromones: 17 alpha,20 beta-dihydroxyprogesterone, 17 alpha,20 beta-dihydroxyprogesterone glucuronide, and 17 alpha-hydroxyprogesterone

A 30-Year Study of Impacts, Recovery, and Development of Critical Effect Sizes for Endocrine Disruption in White Sucker (Catostomus commersonii) Exposed to Bleached-Kraft Pulp Mill Effluent at Jackfish Bay, Ontario, Canada

Jackfish Bay is an isolated bay on the north shore of Lake Superior, Canada that has received effluent from a large bleached-kraft pulp mill since the 1940s. Studies conducted in the late 1980s found evidence of reductions in sex steroid hormone levels in multiple fish species living in the Bay, and increased growth, condition and relative liver weights, with a reduction in internal fat storage, reduced gonadal sizes, delayed sexual maturation, and altered levels of circulating sex steroid hormones in white sucker (Catostomus commersonii). These early studies provided some of the first pieces of evidence of endocrine disruption in wild animals. Studies on white sucker have continued at Jackfish Bay, monitoring fish health after the installation of secondary waste treatment (1989), changes in the pulp bleaching process (1990s), during facility maintenance shutdowns and during a series of facility closures associated with changing ownership (2000s), and were carried through to 2019 resulting in a 30-year study of fish health impacts, endocrine disruption, chemical exposure, and ecosystem recovery. The objective of the present study was to summarize and understand more than 75 physiological, endocrine, chemical and whole organism endpoints that have been studied providing important context for the complexity of endocrine responses, species differences, and challenges with extrapolation. Differences in body size, liver size, gonad size and condition persist, although changes in liver and gonad indices are much smaller than in the early years. Population modeling of the initial reproductive alterations predicted a 30% reduction in the population size, however with improvements over the last couple of decades those population impacts improved considerably. Reflection on these 30 years of detailed studies, on environmental conditions, physiological, and whole organism endpoints, gives insight into the complexity of endocrine responses to environmental change and mitigation.

Excreted Steroids in Vertebrate Social Communication

Steroids play vital roles in animal physiology across species, and the production of specific steroids is associated with particular internal biological functions. The internal functions of steroids are, in most cases, quite clear. However, an important feature of many steroids (their chemical stability) allows these molecules to play secondary, external roles as chemical messengers after their excretion via urine, feces, or other shed substances. The presence of steroids in animal excretions has long been appreciated, but their capacity to serve as chemosignals has not received as much attention. In theory, the blend of steroids excreted by an animal contains a readout of its own biological state. Initial mechanistic evidence for external steroid chemosensation arose from studies of many species of fish. In sea lampreys and ray-finned fishes, bile salts were identified as potent olfactory cues and later found to serve as pheromones. Recently, we and others have discovered that neurons in amphibian and mammalian olfactory systems are also highly sensitive to excreted glucocorticoids, sex steroids, and bile acids, and some of these molecules have been confirmed as mammalian pheromones. Steroid chemosensation in olfactory systems, unlike steroid detection in most tissues, is performed by plasma membrane receptors, but the details remain largely unclear. In this review, we present a broad view of steroid detection by vertebrate olfactory systems, focusing on recent research in fishes, amphibians, and mammals. We review confirmed and hypothesized mechanisms of steroid chemosensation in each group and discuss potential impacts on vertebrate social communication.

Tilapia male urinary pheromone stimulates female reproductive axis

Mozambique tilapia males congregate in leks where they establish dominance hierarchies and attract females to spawn in sandy pits. Dominant males store more urine than subordinates and the pattern of urination and the high sensitivity of females to male urine suggest chemical signalling via the urine. Here we show that pre-ovulated and post-spawn females when exposed to dominant male urine increased significantly, in less than 1h, the release rate of the maturation-inducing steroid 17,20β-dihydroxypregn-4-en-3-one which is maintained elevated for at least 6h. This indicates a pheromonal role for male urine in the synchronisation of spawning. Furthermore, we show that the lack of affinity of 17,20βP to sex steroid binding globulin explains, at least partly, its rapid release and lack of detection in the blood. Thus tilapia urine involvement in several communication processes confirms that cichlids have evolved a sophisticated chemical signalling system together with their complex visual, acoustic and behavioural displays.

In vivo treatment with progestogens causes immunosuppression of carp Cyprinus carpio leucocytes by affecting nitric oxide production and arginase activity

In this study, carp Cyprinus carpio were injected with various steroid compounds, including synthetic and natural progestogens and the glucocorticoid cortisol, to investigate effects on leucocytes isolated from their kidneys. Injection of cortisol led to an increased spleeno-somatic index (I(S)) on day 21 post-injection (pi) and immunosuppressive effects measured as decreased nitric oxide (NO) production and increased arginase activity in isolated leucocytes on days 14 and 21 pi, respectively. Moreover, reduced NO production was also observed after injection of the synthetic progestogens, levonorgestrel (LEV) and medroxyprogesterone acetate. In addition, LEV influenced arginase activity in head kidney cells on day 14 and day 21 pi. This study is the first demonstration in fishes that the application of these steroid compounds in vivo affects NO production and arginase activity of isolated leucocytes.

Responses of white sucker (Catostomus commersoni) to 20 years of process and waste treatment changes at a bleached kraft pulp mill, and to mill shutdown

The impacts of pulp mill effluents on white sucker (Catostomus commersoni) have been studied at Jackfish Bay, ON, Canada since the late 1980s. The site receives effluent from a large bleached kraft pulp mill which is the only source of chemical contamination in the area. Many laboratory studies have looked at the toxicological consequences of pulping process changes, but the benefit of these changes have not been looked at in wild fish. Jackfish Bay white sucker showed impacts on sexual maturity, gonad size, secondary sexual characteristics and circulating steroids hormone levels in the early years of the studies, and impacts were evaluated after installation of secondary treatment (1989), major pulping process changes (1995) and after the mill ceased pulp production and effluent release (2006). The addition of secondary treatment resulted in minor improvements in wild fish health, and the conversion to elemental chlorine free (ECF) bleaching at the mill was associated with more recovery in liver and gonad size. While some impacts persist at the exposure site, reproductive parameters showed further improvement during the mill shutdown period demonstrating that biologically active chemicals are still being discharged from modernized mills.

Measurement of fish steroids in water--a review

Measurement of fish steroids in water provides a non-invasive alternative to measurement in blood samples, offering the following advantages: zero or minimal intervention (i.e. no anaesthetic, bleeding or handling stress); results not being biased by sampling stress; repeat measurements on the same fish; the possibility of making non-lethal measurements on small and/or rare fish; integrating the response of many (or of single) fish; and allowing concurrent monitoring of behaviour or physiology. The procedure is relatively new and, although applications are still fairly limited, there are several themes and potential problem areas that are worthy of review.

Isolation and characterization of the laure olfactory behavioral mutant in the zebrafish, Danio rerio

To initiate a genetic analysis of olfactory development and function in the zebrafish, Danio rerio, we developed a behavioral genetic screen for mutations affecting the olfactory sensory system. First, we characterized olfactory responses of wild-type zebrafish to various odors. We found that 3-day-old juvenile zebrafish reacted to the amino acid L-cysteine with an aversive behavioral response. We isolated one mutant, laure (lre), which showed no aversive behavioral response to L-cysteine at 3 days of development, and carried out a preliminary characterization of this mutant's defects. We found that lre mutant fish were also defective in their response to L-serine and L-alanine, but not to taurocholic acid, as young adults. In addition, lre mutant fish had significantly fewer primary olfactory sensory neurons than normal, and the axons of these neurons did not form the characteristic axon termination pattern in the developing olfactory bulb. Nevertheless, the olfactory epithelium of lre mutant fish showed normal or near normal electrophysiological responses to several odorants. Our data suggest that the behavioral defects observed in the lre mutant result from the disruption of the developing olfactory sensory neurons and their axonal connections within the olfactory bulb. The isolation of the lre mutant shows that our behavior-based screen represents a viable approach for carrying out a genetic dissection of olfactory behaviors in this vertebrate model system.

The role of sex ratio on spawning performance and on the free and conjugated sex steroids released into the water by common dentex (Dentex dentex) broodstock

This paper reports the results of an experiment to determine whether sex ratio has any effect on the spawning efficiency of common dentex, Dentex dentex, broodstock. The paper also reports preliminary data on diurnal changes in water concentrations of steroids (measured on two separate occasions) in the same groups of fish. These latter observations were made to determine whether, using a non-invasive procedure, it was possible to relate hormonal changes in the fish to the "success of spawning." Mature fish were placed in broodstock tanks at three different sex ratios (Group A, 4 female:1 male; Group B, 1 female:1 male; and Group C, 1 female:4 male) and regularly monitored for egg production. At 18 days after the start of spawning, water samples were removed from all three tanks at 130 min intervals over a period of 24 h. At the end of spawning, water samples were removed at 4 h intervals. Free and conjugated steroids were extracted from the water and measured by radioimmunoassay. The highest number of eggs released, percentage of viable eggs, number of spawnings, spawning index, and relative fecundity were observed in Group B (1 female:1 male). The sex steroids testosterone (T), 11-ketotestosterone (11-KT), 17,20beta-P, and 17,20beta, 21-trihydroxy-pregn-4-en-3-one could be readily detected in water from all tanks. Concentrations of the conjugated forms (sulphate and glucuronide) were higher than those of the free form--with the exception of sulphated T and 11-KT. The concentrations of glucuronidated 17,20beta-P, sulphated 17,20beta-P, and free T appeared to be associated with the number of females in the tank and glucuronidated 11-KT concentrations with the number of males. In the first set of water samples (taken during the spawning period) there was also evidence for a cycle in steroid release with an acrophase during the afternoon and early evening, a few hours before the actual act of spawning. We were not able to show any association between steroid concentrations and success of spawning. However, since the data were derived from a "snapshot" of just a single day in what was a prolonged spawning period, this was perhaps not surprising. The results from the present study will help us to design experiments that are more able to answer this question.

Ovarian steroid sulphate functions as priming pheromone in male Barilius bendelisis (Ham.)

The study reveals that pre-ovulatory females of the fish Barilius bendelisis (Ham.) release sex steroids and their conjugates into the water and that a steroid sulphate of these compounds functions as a potent sex pheromone which stimulates milt production in conspecific males prior to spawning. Since males exposed to the purified subfraction III of the steroid sulphate fraction have increased milt volume and more spermatozoa with greater motility, the function of this priming pheromone appears to be to enhance male spawning success. High turbulence and faster water currents render the hillstream ecosystem extremely challenging for chemical communication. Therefore, ovulatory female fish secrete highly water soluble steroid sulphates for rapid pheromonal action in males. Inhibited milt volume in olfactory tract lesioned (OTL) males exposed to the steroid sulphate fraction and 17alpha,20 beta-dihydroxy-4-pregnen-3-one supports the concept that the pheromonally induced priming effect in male fish is mediated through olfactory pathways.

Pheromone discrimination ability of olfactory bulb mitral and ruffed cells in the goldfish (Carassius auratus)

Significant anatomical differences characterizing mitral cells and ruffed cells were published by Kosaka and Hama in three teleost species. Physiological responses from both types of relay neurons have now been recorded extracellularly and simultaneously in the plexiform layer using a single tungsten microelectrode. During interstimulus intervals mitral cells responded with higher, frequently burst-like impulse rates triggered by the activity of epithelial receptor neurons. Ruffed cell impulse rates were low, and each action potential triggered a long-lasting, continuously variable, integrated granule cell potential. During olfactory stimulation with important biological stimuli such as preovulatory and ovulatory pheromones, a probable alarm pheromone and amino acids contrasting interactions between mitral cells and ruffed cells resulting in a drastic intensification of centrally transmitted information were frequently recorded. Individual neurons excellently discriminated stimuli. Irrespective of the physiological relevance of stimuli, however, similarities were recorded in the distribution of excitatory, inhibitory and indifferent responses.

Overripening as the cause of low survival to hatch in Lake Erie coho salmon (Oncorhynchus kisutch) embryos

We investigated the cause of the low survival to hatch of embryos of coho salmon (Oncorhynchus kisutch) from the Fairview, Pennsylvania, stock in Lake Erie. In 1988, survival to hatch of this stock was only 42%, whereas another Great Lakes coho salmon stock of similar genetic origin had an 84% survival to hatch. Laboratory cross-fertilization studies between the Fairview stock and a reference Lake Erie stock from Simcoe, Ontario, showed that eggs from the Fairview stock were the probable source of the low fertility. The presence of overripe eggs in Fairview females was associated with poor fertilization and low survival to hatch. Plasma gonadotropin II levels were similar in preovulatory females taken from the Fairview and Simcoe stocks, but testosterone and 17α, 20β-dihydroxy-4-pregnen-3-one levels were significantly lower in the Fairview females. Increasing the triiodo-L-thyronine (T3) content of the eggs by the administration of T3 to the preovulatory females did not enhance egg fertility. We propose that the low survival to hatch of the Fairview embryos is due to delayed oocyte maturation and ovulation and vent maturation, which may have been caused by exposure of the Fairview salmon to warmer water during the period of late ovarian maturation and migration.

The evolution of hormonal sex pheromones in teleost fish: poor correlation between the pattern of steroid release by goldfish and olfactory sensitivity suggests that these cues evolved as a result of chemical spying rather than signal specialization

It is becoming increasingly evident that many teleost fish use hormones and their metabolites as sex pheromones. Although hormonal pheromone systems of several species of fish have now been characterized, that of the goldfish is the best understood. Reproductively-active female goldfish sequentially release derivatives of three steroidal hormones and two prostaglandins which have specific and potent actions on the goldfish olfactory sense and subsequently conspecific reproductive behaviour and physiology. Three goldfish hormonal pheromones are unmodified sex hormones which are also found in the blood of many other species of fish and are therefore unlikely to be species-specific. This scenario evokes two related questions. First, how did these systems evolve? Second, do hormonal pheromones represent specialized signals used for communication or rather simple metabolites which fish have evolved the ability to detect because of their intrinsic meaning ('spying')? Here we review hormonal pheromone function in fish and then describe a study of the goldfish which tests whether hormonal pheromones are specialized communicatory signals by comparing the profile of steroids released by goldfish with their olfactory responsiveness to these compounds. Little correlation between signal production and detection was found and we conclude that the goldfish hormonal pheromone system most likely exemplifies spying.

In vitro biosynthesis of steroids, including 11-deoxycortisol and 5 alpha-pregnane-3 beta,7 alpha,17,20 beta-tetrol, by ovaries of the goldfish Carassius auratus during the stage of oocyte final maturation

To examine the production of steroids with potential oocyte maturation-inducing or pheromonal activity in the goldfish (Carassius auratus) we have incubated mature ovaries of this species with 17-[3H]hydroxyprogesterone. The metabolites in the unconjugated, glucuronide, and sulfate fractions were identified by chromatography, microchemical reaction, and, in most cases, crystallization to constant specific activity. A major metabolite, present in all three fractions, was tentatively identified as 5 alpha-pregnane-3 beta,7 alpha,17,20 beta-tetrol. Although 17,20 beta-dihydroxy-4-pregnen-3-one (17,20 beta-P) was found in only low yield (as a sulfate), the presence of the tetrol indicates that it is synthesized in high yield but very rapidly metabolized. The relative proportions of 17,20 alpha-dihydroxy-4-pregnen-3-one (17,20 alpha-P), 11-deoxycortisol (17,21-dihydroxy-4-pregnen-3,20-dione) and 17,20 beta,21-trihydroxy-4-pregnen-3-one (17,20 beta,21-P) varied significantly between incubations and may be affected by the maturational state of the ovary or the method used to stimulate oocyte maturation. Testosterone was present predominantly as its glucuronide. Significant production of glucuronides and sulfates was observed in all incubations. Twenty-five to 30% of the radioactivity remained associated with the tissue, but the distribution of activity between the metabolites did not differ greatly from that found in the medium. These results indicate that 11-deoxycortisol and its 20 beta-reduced derivative (17,20 beta,21-P) may be significant in spawning female goldfish.

Exposure to bleached kraft pulp mill effluent disrupts the pituitary-gonadal axis of white sucker at multiple sites

Our recent studies have demonstrated reproductive problems in white sucker (Catostomus commersoni) exposed to bleached kraft pulp mill effluent (BKME) at Jackfish Bay on Lake Superior. These fish exhibit delayed sexual maturity, reduced gonadal size, reduced secondary sexual characteristics, and circulating steroid levels depressed relative to those of reference populations. The present studies were designed to evaluate sites in the pituitary-gonadal axis of prespawning white sucker affected by BKME exposure. At the time of entry to the spawning stream, plasma levels of immunoreactive gonadotropin (GtH)-II (LH-type GtH) in male and female white sucker were 30- and 50-fold lower, respectively, than the levels in fish from a reference site. A single intraperitoneal injection of D-Arg6, Pro9N-Et sGnRH (sGnRH-A, 0.1 mg/kg) increased plasma GtH levels in male and female fish at both sites, although the magnitude of the response was greatly reduced in BKME-exposed fish. Fish at the BKME site did not ovulate in response to sGnRH-A, while 10 of 10 fish from the reference site ovulated within 6 hr. Plasma 17 alpha,20 beta-dihydroxy-4-pregnen-3-one (17,20 beta-P) levels were depressed in BKME-exposed fish and unlike fish at the reference site, failed to increase in response to sGnRH-A. Testosterone levels in both sexes and 11-ketostestosterone levels in males were elevated in fish from the reference site but were not further increased by GnRH treatment. In contrast, BKME-exposed fish exhibit a transitory increase in testosterone levels in response to the GnRH analog. In vitro incubations of ovarian follicles obtained from fish at the BKME site revealed depressed basal secretion of testosterone and 17,20 beta-P and reduced responsiveness to the GtH analog human chorionic gonadotropin and to forskolin, a direct activator of adenylate cyclase. By comparison, ovarian follicles from fish collected at BKME and reference sites produced similar levels of prostaglandin E basally and in response to a phorbol ester and calcium ionophore A23187, suggesting that BKME effects on ovarian function are selective and do not reflect a general impairment of ovarian function. BKME-exposed fish had plasma levels of testosterone glucuronide proportionately lower than those of reference fish, suggesting that there are site differences in the peripheral metabolism of steroids. These studies demonstrate that BKME exposure affects reproduction by acting at multiple sites in the pituitary-gonadal axis.

Multiplicity of UDP-glucuronosyltransferases in fish. Purification and characterization of a phenol UDP-glucuronosyltransferase from the liver of a marine teleost, Pleuronectes platessa

The aim of this work was to determine if a non-mammalian species had multiple UDP-glucuronosyltransferase (UDPGT) isoforms. At least six highly purified UDPGT isoenzymes were partially resolved by anion-exchange chromatography and UDP-hexanolamine-Sepharose 4B affinity chromatography from liver microsomes of a fish, the plaice. Q-Sepharose FF, chromatofocusing and affinity-chromatographic procedures were employed to separate and purify the phenol UDPGT isoform to apparent homogeneity. The purified enzyme conjugated 1-naphthol, but not bilirubin or steroids, and displayed a pI of 7.0 and a subunit molecular mass of 55 kDa. Bilirubin and testosterone UDPGT activities were more labile and, although purified over 200-fold, these preparations also contained the phenol UDPGT and had multiple polypeptides with molecular masses of 52-57 kDa. Antisera to rat bilirubin/phenol UDPGT and testosterone/phenol UDPGT isoforms cross-reacted strongly with the partially purified plaice UDPGT isoforms of molecular masses 52, 53 and 57 kDa and less strongly with phenol UDPGT 54 kDa and 56 kDa isoforms. Fish and mammalian UDPGTs therefore apparently possess a high degree of evolutionary conservation.

Properties of common carp gonadotropin I and gonadotropin II

Two gonadotropins, GtH I and GtH II, were extracted with 35% ethanol-10% ammonium acetate, pH 6.1, from female common carp pituitary glands and purified by ion-exchange chromatography on a DE-52 column followed by gel filtration on a Sephadex G-75 column. Molecular weights of GtH I and GtH II as determined by SDS-PAGE were 45,000 and 35,000, respectively. Both GtHs dissociate into two subunits following reduction with beta-mercaptoethanol. These subunits contain different N-terminal amino acids (Tyr and Gly for GtH I; Tyr and Ser for GtH II). GtH I was acid stable and did not dissociate into subunits following treatment with 0.1% trifluoroacetic acid; GtH II readily dissociated into subunits by this treatment. GtH I and GtH II have distinct elution profiles on reverse-phase HPLC. The N-terminal amino acid sequence of the beta-subunit of GtH II was identical to that of common carp maturational GtH described by other workers suggesting that GtH I is a newly identified molecule. This was supported by radioimmunoassay analysis. GtH II and a common carp maturational GtH preparation (F11 cGtH; Peter et al., 1982, J. Interdiscipl. Cycle Res. 13, 229-239) had similar immunological activity in tests with antisera to the beta-subunit of maturational GtH whereas GtH I had low (less than 6%) cross-reactivity. GtH I, GtH II, and F11 cGtH were equipotent in tests with antisera to the alpha-subunit of maturational GtH suggesting these molecules contain a similar alpha-subunit. In vitro bioassays using goldfish revealed that GtH I and GtH II share the same spectrum of biological activities causing stimulation of ovarian and testicular steroidogenesis and induction of oocyte final maturation. The demonstration of two chemically distinct GtHs in common carp is similar to what has been described for chum and coho salmon.

Differing behavioral and endocrinological effects of two female sex pheromones on male goldfish

Ovulatory female goldfish sequentially release at least two sex pheromones: 17 alpha, 20 beta-dihydroxy-4-pregnen-3-one (17,20 beta P) and a mixture of F prostaglandins (PGFs). This study sought to determine whether these pheromones have different endocrinological and behavioral actions and whether the PGF pheromone, which is released by spawning females, is responsible for increasing the gonadotropin (GtH) and milt (sperm and seminal fluid) levels of spawning males. Grouped and isolated males were exposed to combinations of these pheromones, food odor, and spawning and nonspawning females. 17,20 beta P stimulated GtH increases in both grouped and isolated males but had only minor effects on behavior; because its principal function appears to be physiological it may be considered a "primer" pheromone. In contrast, exposue to the PGFs elicited large increases in sexual behavior but increased GtH only when fish were exposed as groups; this pheromone's principal action appears to be behavioral and it should be considered a "releaser" pheromone. Although males had increased GtH and milt levels after 1 hr of spawning, males allowed to interact with nonspawning females also had elevated GtH; thus, behavioral interactions appear capable of elevating GtH in the absence of either pheromone. The existence of an independent behavioral mechanism which stimulates GtH was supported by the fact that males exposed to 17,20 beta P while spawning had GtH levels much greater than males exposed to only one of these stimuli.

Direct evidence that 17 alpha,20 beta-dihydroxy-4-pregnen-3-one functions as a goldfish primer pheromone: preovulatory release is closely associated with male endocrine responses

This study directly tested the hypothesis that 17 alpha,20 beta-dihydroxy-4-pregnen-3-one (17,20 beta-P) is a goldfish preovulatory pheromone (pheromone released at peak levels during oocyte final maturation) which increases blood gonadotropin (GtH) and milt volume in males. During spontaneous ovulation, GtH and 17,20 beta-P in female blood and 17,20 beta-P released to the water increased dramatically 7-10 hr prior to ovulation, peaked 1-4 hr prior to ovulation, and then rapidly declined. Males held with these females, or exposed to their odors, had increased GtH levels and milt volumes at approximately the time when increased 17,20 beta-P release by ovulatory females commenced. Although these findings strongly support the hypothesis that 17,20 beta-P is a preovulatory female sex pheromone in goldfish which stimulates male GtH levels and milt production prior to spawning, the milt increases occurred earlier than predicted, suggesting either that preovulatory 17,20 beta-P release begins earlier than the data indicate or that other steroids known to have pheromonal activity are released before 17,20 beta-P.