The deleterious effects of cortisol implantation on reproductive function in two species of trout, Salmo trutta L. and Salmo gairdneri Richardson

Challenges and Recommendations in Assessing Potential Endocrine-Disrupting Properties of Metals in Aquatic Organisms

New tools and refined frameworks for identifying and regulating endocrine-disrupting chemicals (EDCs) are being developed as our scientific understanding of how they work advances. Although focus has largely been on organic chemicals, the potential for metals to act as EDCs in aquatic systems is receiving increasing attention. Metal interactions with the endocrine system are complicated because some metals are essential to physiological systems, including the endocrine system, and nonessential metals can have similar physiochemical attributes that allow substitution into or interference with these systems. Consequently, elevated metal exposure could potentially cause endocrine disruption (ED) but can also cause indirect effects on the endocrine system via multiple pathways or elicit physiologically appropriate compensatory endocrine-mediated responses (endocrine modulation). These latter two effects can be confused with, but are clearly not, ED. In the present study, we provide several case studies that exemplify the challenges encountered in evaluating the endocrine-disrupting (ED) potential of metals, followed by recommendations on how to meet them. Given that metals have multiple modes of action (MOAs), we recommend that assessments use metal-specific adverse outcome pathway networks to ensure that accurate causal links are made between MOAs and effects on the endocrine system. We recommend more focus on establishing molecular initiating events for chronic metal toxicity because these are poorly understood and would reduce uncertainty regarding the potential for metals to be EDCs. Finally, more generalized MOAs such as oxidative stress could be involved in metal interactions with the endocrine system, and we suggest it may be experimentally efficient to evaluate these MOAs when ED is inferred. These experiments, however, must provide explicit linkage to the ED endpoints of interest. Environ Toxicol Chem 2023;42:2564-2579. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Reproductive endocrine disruption and gonadal intersex induction in male Japanese medaka chronically exposed to betamethasone at environmentally relevant levels

The broad utilization of betamethasone in medical treatments may pose a significant ecotoxicological risk to aquatic organisms, yet its potential reproductive toxicity remains unclear. The present study examined the impacts of environmental exposure on male reproduction using Japanese medaka (Oryzias latipes). After 110 days of betamethasone exposure at environmentally relevant concentrations (0, 20 and 200 ng/L), LH/FSH synthesis and release in the pituitary was inhibited, and the production of sex hormones and their signaling pathways in the gonads of male medaka were greatly influenced. This synthetic glucocorticoid restrained testosterone (T) synthesis and gave rise to a significant increase in E₂/T and E₂/11-KT ratios. Furthermore, chronic betamethasone exposure (20 and 200 ng/L) led to the suppression of androgen receptor (AR) signaling and enhancement of estrogen receptors (ERs) signaling. An increase in hepatic vitellogenin contents was also detected, and testicular oocytes were observed in both 20 and 200 ng/L betamethasone-treated groups. It showed that 20 and 200 ng/L betamethasone could induce male feminization and even intersex, triggering abnormal spermatogenesis in medaka males. With its adverse effects on male fertility, betamethasone could potentially influence the fishery productivity and population dynamics in aquatic ecosystems.

Chronic exposure to environmental concentrations of harmful algal bloom-forming dinoflagellates induces oxidative stress and reduces immune and hepatic functions in red seabream

Harmful algal blooms (HABs) caused by dinoflagellates can be detrimental to aquaculture and fisheries. However, little is known regarding their ichthyotoxic effects on fish, particularly after chronic exposure to sublethal levels. In this study, significant modulations in physiology, immunity, antioxidant components, and hepatic indicators owing to non-toxin-producing dinoflagellate strains (Alexandrium affine and Cochlodinium polykrikoides) were analyzed in juvenile red seabream, Pagrus major, exposed to sublethal concentrations (0, 1, and 100 cells mL^-1) for 60 days. At 60 days, higher mortality was induced by A. affine than by C. polykrikoides. Significant increases in respiration rate and plasma cortisol were observed in red seabream exposed to 100 cells mL^-1 of the two dinoflagellates. Intracellular reactive oxygen species and malondialdehyde levels were significantly elevated in the gill and liver tissues in response to 100 cells mL^-1 of either dinoflagellate. Immunity parameters such as alternative complement activity, lysozyme activity, and total immunoglobulin content were significantly decreased during exposure to 100 cells mL^-1 of the two dinoflagellates. Although no significant change was observed in the gonadosomatic index, the hepatosomatic index was significantly decreased by exposure to 100 cells mL^-1 of the two dinoflagellates on day 60. The significant decrease in enzymatic activities of ethoxyresorufin-O-deethylase, alanine aminotransferase, aspartate aminotransferase, and alkaline phosphatase upon exposure to 100 cells mL^-1 of either dinoflagellate suggested impaired hepatic function through prolonged exposure. Our results suggest that consistent exposure to sublethal concentrations of HAB-forming dinoflagellates is detrimental to fish physiology and biochemical defenses.

Are synthetic glucocorticoids in the aquatic environment a risk to fish?

The glucocorticosteroid, or glucocorticoid (GC), system is largely conserved across vertebrates and plays a central role in numerous vital physiological processes including bone development, immunomodulation, and modification of glucose metabolism and the induction of stress-related behaviours. As a result of their wide-ranging actions, synthetic GCs are widely prescribed for numerous human and veterinary therapeutic purposes and consequently have been detected extensively within the aquatic environment. Synthetic GCs designed for humans are pharmacologically active in non-mammalian vertebrates, including fish, however they are generally detected in surface waters at low (ng/L) concentrations. In this review, we assess the potential environmental risk of synthetic GCs to fish by comparing available experimental data and effect levels in fish with those in mammals. We found the majority of compounds were predicted to have insignificant risk to fish, however some compounds were predicted to be of moderate and high risk to fish, although the dataset of compounds used for this analysis was small. Given the common mode of action and high level of inter-species target conservation exhibited amongst the GCs, we also give due consideration to the potential for mixture effects, which may be particularly significant when considering the potential for environmental impact from this class of pharmaceuticals. Finally, we also provide recommendations for further research to more fully understand the potential environmental impact of this relatively understudied group of commonly prescribed human and veterinary drugs.

Analysis of neuroendocrine factors in response to conditional stress in zebrafish Danio rerio (Cypriniformes: Cyprinidae)

Challenges in the aquatic environment disrupt the homeostasis mechanisms of many teleost fishes. Induction of stress affects the circulating levels of catecholamine and has an impact on development and reproduction. It is not known how osmotic and hypoxic stress could affect the catecholamine and serotonin levels in zebrafish despite its well-known action in the vertebrate brain. This study thus investigates how serotonin (5-HT), epinephrine (E), norepinephrine (NE), and dopamine (DA) in the brain of female zebrafish respond to hypoxic (air) and osmotic conditions (salinity of 10 ppt). Analysis of zebrafish brain utilizing HPLC with PDA detector using reverse-phase PrimeSep column indicated that osmotic stress, air response and its combination modified 5-HT, NE and E levels. The tested stressors elevated 5-HT (>2.8 μM) while lowering NE (<3.00 μM) and E (<1.02 μM) levels in the brain as opposed to exposure to non-stressed fish. In addition, reproductive markers such as vitellogenin (Vtg1) and estrogen receptor (ERα) mRNA expression in the brain were up-regulated after osmotic stress, whereas air exposure down-regulated ERα mRNA expression but up-regulated Vtg1 compared to non-stressed fish. Overall, the data indicate that acute osmotic stress and air exposure that lowered catecholamine E and NE and elevated 5-HT levels could up-regulate mRNA expression of ERα and Vtg1 genes in the zebrafish brain, thus presenting evidence for a role of neurotransmitters on reproductive signals during acute conditional stress in the brain of wild zebrafish.

Exogenous cortisol and red light irradiation affect reproductive parameters in the goldfish Carassius auratus

Reproductive hormones play essential roles in the control of reproduction and gonadal maturation in fish. The purpose of this study was to determine the effects of cortisol administration (10 µg/g or 50 µg/g) or red light irradiation at two intensities (0.5 W/m² or 1.0 W/m²) on the reproductive hormones in goldfish (Carassius auratus). The effects of different treatments were analyzed by determining the mRNA expression levels of gonadotropin-inhibitory hormone receptor (GnIH-R), chicken gonadotropin-releasing hormone (cGnRH-II), salmon GnRH (sGnRH), FSHβ, LHβ, and plasma testosterone and the level of 17β-estradiol for 48 h. Additionally, by double immunofluorescence staining, we detected the expression of both GnIH and GnRH in the diencephalons of goldfish brains. The mRNA expression of GnIH-R was significantly higher in the cortisol group and red light-irradiated group from 3 to 48 h than in the control group. Additionally, the mRNA levels of cGnRH-II, sGnRH, FSHβ, LHβ, testosterone, and 17β-estradiol were significantly lower in the cortisol group than in the other groups from 3 to 48 h. These results indicated that both cortisol and red light-emitting diode (LED) light increased GnIH expression and inhibited GnRH expression. In particular, red light irradiation suppressed reproductive responses as much as the cortisol treatment at 48 h. Thus, it could be an alternative method for suppressing reproductive responses in future aquacultures.

Turning the spotlight on the C11-oxy androgens in human fetal development

Research into the biosynthesis of C11-oxy C₁₉ steroids during human fetal development, specifically fetal adrenal development and during the critical period of sex differentiation, is currently lacking. Cortisol, which possesses a C11-hydroxyl moiety has, however, been firmly established in this context. Compelling questions are whether the C11-oxy C₁₉ steroids (11β-hydroxyandrostenedione, 11β-hydroxytestosterone, 11-ketoandrostenedione and 11-ketotestosterone [11KT]) and the C11-oxy C₂₁ steroids (11β-hydroxyprogesterone and 11-ketoprogesterone) are biosynthesised during gestation, and whether these hormones circulate between the placenta and the developing fetus, and between the placenta and the mother. This review will consider the role of cortisol, 11KT and 11β-hydroxysteroid dehydrogenase type 2 (11βHSD2) in determining the sex of teleost fish, while these hormones and 11βHSD2 will also be discussed with regards to murine mammals. The focus of the review will shift to highlight the potential role of C11-oxy steroids in human fetal development based on the timely expression of steroidogenic enzymes in the adrenal, testes and ovary, as well as in the placenta; summarising reported evidence of C11-oxy steroids in neonatal life.

Atresia of ovarian follicles in fishes, and implications and uses in aquaculture and fisheries

Atresia of ovarian follicles, that is the degenerative process of germ cells and their associated somatic cells, is a complex process involving apoptosis, autophagy and heterophagy. Follicular atresia is a normal component of fish oogenesis and it is observed throughout the ovarian cycle, although it is more frequent in regressing ovaries during the postspawning period. An increased occurrence of follicular atresia above physiological rates reduces fish fecundity and even causes reproductive failure in both wild and captive-reared fish stocks, and hence, this phenomenon has a wide range of implications in applied sciences such as fisheries and aquaculture. The present article reviews the available literature on both basic and applied traits of oocyte loss by atresia, including its morpho-physiological aspects and factors that cause a supraphysiological increase of follicular atresia. Finally, the review presents the use of early follicular atresia identification in the selection process of induced spawning in aquaculture and the implications of follicular atresia in fisheries management.

Special features of neuroendocrine interactions between stress and reproduction in teleosts

Stress and reproduction are both essential functions for vertebrate survival, ensuring on one side adaptative responses to environmental changes and potential life threats, and on the other side production of progeny. With more than 25,000 species, teleosts constitute the largest group of extant vertebrates, and exhibit a large diversity of life cycles, environmental conditions and regulatory processes. Interactions between stress and reproduction are a growing concern both for conservation of fish biodiversity in the frame of global changes and for the development of sustainability of aquaculture including fish welfare. In teleosts, as in other vertebrates, adverse effects of stress on reproduction have been largely documented and will be shortly overviewed. Unexpectedly, stress notably via cortisol, may also facilitate reproductive function in some teleost species in relation to their peculiar life cyles and this review will provide some examples. Our review will then mainly address the neuroendocrine axes involved in the control of stress and reproduction, namely the corticotropic and gonadotropic axes, as well as their interactions. After reporting some anatomo-functional specificities of the neuroendocrine systems in teleosts, we will describe the major actors of the corticotropic and gonadotropic axes at the brain-pituitary-peripheral glands (interrenals and gonads) levels, with a special focus on the impact of teleost-specific whole genome duplication (3R) on the number of paralogs and their potential differential functions. We will finally review the current knowledge on the neuroendocrine mechanisms of the various interactions between stress and reproduction at different levels of the two axes in teleosts in a comparative and evolutionary perspective.

The effect of teprenone on the intestinal morphology and microbial community of Chinese sea bass (Lateolabrax maculatus) under intermittent hypoxic stress

Hypoxia stress may affect the fish intestine and thereby threaten the growth and survival of the fish. Teprenone is a clinically effective agent in protecting gastrointestinal mucosa. This study aims to assess the effect of teprenone in the intestine of Chinese sea bass Lateolabrax maculatus under intermittent hypoxic stress. L. maculatus juveniles were either raised under intermittent hypoxic condition or normal condition (NC). Part of the hypoxic-intervened fish were treated with teprenone at different concentrations (HTs), and the rest were regarded as hypoxic control (HC). Histological analysis was performed on the epithelial tissue of the fish intestine. High-throughput sequencing technology was used to analyze the diversity and composition of the microbial community in L. maculatus intestine. Reduced villi length and goblet cell, exfoliated enterocyte, and improper arrangement of villi were observed in HC compared with NC and HTs. Proteobacteria, Firmicutes, and Bacteroidetes represented the most abundant phyla in each sample. Significantly higher microbial diversity was detected in HC compared with NC (P < 0.05). At the phylum level, HC presented significantly decreased relative abundance of Proteobacteria, and significantly increased relative abundance of Bacteroidetes, Chloroflex, and Cyanobacteria compared with NC (P < 0.05). At the class level, HC showed significantly reduced relative abundance of Alphaproteobacteria and Bacilli, and significantly increased relative abundance of Clostridia, Gammaproteobacteria, and Bacteroides (P < 0.05). Teprenone protects the intestine from epithelial damages and maintains the microbial harmony in L. maculatus under intermittent hypoxic stress.

Reduced lactate dehydrogenase activity in the heart and suppressed sex hormone levels are associated with female-biased mortality during thermal stress in Pacific salmon

Female-biased mortality has been repeatedly reported in Pacific salmon during their upriver migration in both field studies and laboratory holding experiments, especially in the presence of multiple environmental stressors, including thermal stress. Here, we used coho salmon (Oncorhynchus kisutch) to test whether females exposed to elevated water temperatures (18°C) (i) suppress circulating sex hormones (testosterone, 11-ketotestosterone and estradiol), owing to elevated cortisol levels, (ii) have higher activities of enzymes supporting anaerobic metabolism (e.g. lactate dehydrogenase, LDH), (iii) have lower activities of enzymes driving oxidative metabolism (e.g. citrate synthase, CS) in skeletal and cardiac muscle, and (iv) have more oxidative stress damage and reduced capacity for antioxidant defense [lower catalase (CAT) activity]. We found no evidence that a higher susceptibility to oxidative stress contributes to female-biased mortality at warm temperatures. We did, however, find that females had significantly lower cardiac LDH and that 18°C significantly reduced plasma levels of testosterone and estradiol, especially in females. We also found that relative gonad size was significantly lower in the 18°C treatment regardless of sex, whereas relative liver size was significantly lower in females held at 18°C. Further, relative spleen size was significantly elevated in the 18°C treatments across both sexes, with larger warm-induced increases in females. Our results suggest that males may better tolerate bouts of cardiac hypoxia at high temperature, and that thermal stress may also disrupt testosterone- and estradiol-mediated protein catabolism, and the immune response (larger spleens), in migratory female salmon.

Cortisol Directly Stimulates Spermatogonial Differentiation, Meiosis, and Spermiogenesis in Zebrafish (Danio rerio) Testicular Explants

Cortisol is the major endocrine factor mediating the inhibitory effects of stress on vertebrate reproduction. It is well known that cortisol affects reproduction by interacting with the hypothalamic–pituitary–gonads axis, leading to downstream inhibitory and stimulatory effects on gonads. However, the mechanisms are not fully understood. In this study, we provide novel data demonstrating the stimulatory effects of cortisol on spermatogenesis using an ex vivo organ culture system. The results revealed that cortisol treatment did not modulate basal androgen production, but it influenced transcript levels of a selected number of genes involved in the zebrafish testicular function ar (androgen receptor), star (steroidogenic acute regulatory), cyp17a1 (17α-hydroxylase/17,20 lyase/17,20 desmolase), cyp11a2 (cytochrome P450, family 11, subfamily A, polypeptide 2), hsd11b2 (11-beta hydroxysteroid dehydrogenase), cyp2k22 (cytochrome P450, family 2, subfamily K, polypeptide 22), fkbp5 (FKBP prolyl isomerase 5), grα (glucocorticoid receptor alpha), and grβ (glucocorticoid receptor beta) in a short-term culture. We also showed that cortisol stimulates spermatogonial proliferation and differentiation in an androgen independent manner as well as promoting meiosis and spermiogenesis by increasing the number of spermatozoa in the testes. Moreover, we demonstrated that concomitant treatment with RU 486, a potent glucocorticoid receptor (Gr) antagonist, did not affect the cortisol effects on spermatogonial differentiation but blocked the induced effects on meiosis and spermiogenesis. Supporting the Gr-mediated effects, RU 486 nullified the cortisol-induced expression of sycp3l (synaptonemal complex protein 3), a marker for the meiotic prophase that encodes a component of the synaptonemal complex. This is consistent with in silico analysis that found 10 putative GREs (glucocorticoid response elements) upstream of the zebrafish sycp3l. Finally, we also showed that grα mRNA is expressed in Sertoli and Leydig cells, but also in several types of germ cells, including spermatogonia and spermatocytes. Altogether, this evidence indicates that cortisol exerts paracrine roles in the zebrafish testicular function and spermatogenesis, highlighting its effects on spermatogonial differentiation, meiosis, and spermiogenesis.

Experimental manipulation of perceived predation risk and cortisol generates contrasting trait trajectories in plastic crucian carp

Most animals constitute potential prey and must respond appropriately to predator-mediated stress in order to survive. Numerous prey also adaptively tailor their response to the prevailing level of risk and stress imposed by their natural enemies, i.e. they adopt an inducible defence strategy. Predator exposure may activate the stress axis, and drive the expression of anti-predator traits that facilitate survival in a high-risk environment (the predation-stress hypothesis). Here, we quantified two key morphological anti-predator traits, body morphology and coloration, in crucian carp reared in the presence or absence of a predator (pike) in addition to experimental manipulation of physiological stress via implants containing either cortisol or a cortisol inhibitor. We found that predator-exposed fish expressed a deeper-bodied phenotype and darker body coloration as compared with non-exposed individuals. Skin analyses revealed that an increase in the amount of melanophores caused the dramatic colour change in predator-exposed fish. Increased melanization is costly, and the darker body coloration may act as an inducible defence against predation, via a conspicuous signal of the morphological defence or by crypsis towards dark environments and a nocturnal lifestyle. By contrast, the phenotype of individuals carrying cortisol implants did not mirror the phenotype of predator-exposed fish but instead exhibited opposite trajectories of trait change: a shallow-bodied morphology with a lighter body coloration as compared with sham-treated fish. The cortisol inhibitor did not influence the phenotype of fish i.e. neither body depth nor body coloration differed between this group and predator-exposed fish with a sham implant. However, our results illuminate a potential link between stress physiology and morphological defence expression.

Effects of the glucocorticoid clobetasol propionate and its mixture with cortisol and different class steroids in adult female zebrafish

Ecotoxicological effects of glucocorticoids and steroid mixtures in the environment are not sufficiently known. Here we investigate effects of 11-14 days exposure of female zebrafish to the glucocorticoid clobetasol propionate (Clo), cortisol (Cs), their mixture and mixtures with five different class steroids (Clo + triamcinolone + estradiol + androstenedione + progesterone) in liver, brain and gonads. Cs showed little activity, while Clo reduced the condition factor at 0.57 and 6.35 μg/L. Clo induced differential expression of genes in the liver at 0.07-6.35 μg/L, which were related to circadian rhythm (per1, nr1d2), glucose metabolism (g6pca, pepck1), immune system response (fkbp 5, socs3, gilz), nuclear steroid receptors (pgr and pxr), steroidogeneses and steroid metabolism (hsd11b2, cyp2k22). Clo caused strong transcriptional down-regulation of vtg. Similar upregulations occurred in the brain for pepck1, fkbp5, socs3, gilz, hsd11b2, and nr1d2a, while cyp19b was down-regulated. Effects of Clo + Cs mixtures were similar to Clo alone. Transcriptional alterations were different in mixtures of five steroids with no alteration of vtg in the liver due to counteraction of Clo and estradiol. Induction of fkbp5 (brain) and sult2st3 (liver) and downregulation of cyp19a (gonads) occurred at 1 μg/L. Histological effects of the five steroids mixture in gonads were characterized by a decrease of mature oocytes. Our data indicate that effects of steroids of different classes sum up to an overall joint effect driven by the most potent steroid Clo.

Cortisol differentially affects cell viability and reproduction-related gene expression in Atlantic cod pituitary cultures dependent on stage of sexual maturation

Through the action of cortisol, stress can affect reproductive biology with behavioural and physiological alterations. Using mixed sex primary pituitary cultures from Atlantic cod (Gadus morhua), the present study aimed to investigate potential direct effects of basal and stress level cortisol on the pituitary in terms of cell viability and reproduction-related gene expression at different stages of sexual maturity. Stress level of cortisol stimulated cell viability in cells derived from sexually maturing and mature fish. In cells from spent fish, high cortisol levels did not affect cell viability in terms of metabolic activity, but did stimulate viability in terms of membrane integrity. Basal cortisol levels did not affect cell viability. Ethanol, used as solvent for cortisol, decreased cell viability at all maturity stages, but did generally not affect gene expression. Genes investigated were fshb, lhb and two Gnrh receptors expressed in cod gonadotropes (gnrhr1b and gnrhr2a). Cortisol had dual effects on fshb expression; stimulating expression in cells from mature fish at stress dose, while inhibiting expression in cells from spent fish at both doses. In contrast, cortisol had no direct effect on lhb expression. While gnrhr2a transcript levels largely increased following cortisol treatment, gnrhr1b expression decreased in cells from spent fish and was unaffected at other maturity stages. These findings demonstrate that cortisol can act directly and differentially at the pituitary level in Atlantic cod and that factors facilitating these actions are dose-dependently activated and vary with level of sexual maturity.

Corticosteroids deeply depress the in vitro steroidogenic capacity of Eurasian perch ovary at the end of the reproductive cycle

Corticosteroids play positive or negative role in the reproductive mechanisms of many fish species but the physiological contexts relating to such biphasic actions are not well defined. In the present study we investigated to what extent corticosteroids (cortisol-Co, 11-deoxycorticosterone-DOC) hormones may interfere with the steroidogenic capacity of Eurasian perch ovarian tissues, and we tested whether the negative effects of corticosteroids may be mitigated by potential stimulating endocrine factors, namely insulin-like growth factor-1 (IGF), human chorionic gonadotropin (HCG) or thyroid hormones (Triidothyronine-T3, thyroxine-T4). Ovarian tissues from six maturing fish at late vitellogenesis developmental stage (LVO) or at the start of the final meiotic oocyte maturation (FMO) were incubated during 6h in Cortland medium containing various endocrine compounds. Both corticosteroids drastically suppressed aromatase activity (AA) and sex-steroid production, namely 17-β estradiol (E2), 17α-20β-dihydroxy-4-pregnen-3-one (DHP) and testosterone (T). HCG significantly prevented the suppression of both AA and sex-steroid production by low and high cortisol doses, but a lesser AA protection was observed in the case of DOC. The protection of DHP and T productions by HCG from the negative effects by the two corticosteroids was higher at FMO than at LVO stage. IGF or thyroid hormone treatments were lesser effective or ineffective in mitigating the suppression of AA or sex-steroid production by cortisol. The results suggest that an increase in cortisol or DOC such as after mild or high stress intensity may inhibit drastically the ovarian steroidogenic capacity whatever the final oocyte maturation stage in percid fish by hampering AA and sex-steroid production. That inhibition may be partly mitigated by gonadotropins but not IGF nor thyroid hormones, especially at final meiotic oocyte maturation stage.

Stressor timing, not cortisol, is an important embryo viability determinant in female rainbow trout Oncorhynchus mykiss

The objective of this study was to determine whether the timing of elevated cortisol levels in adult female rainbow trout Oncorhynchus mykiss, achieved by silastic implants within the body cavity, had an effect on embryo viability. Cortisol-implanted fish experienced a significant increase in circulating levels of plasma cortisol compared with sham-implanted fish, and plasma cortisol remained elevated relative to sham-implanted fish for 4 months in each of the three treatment groups (0-4, 4-8 and 8-12 months). There were no significant differences in embryo viability, egg diameters or plasma 17β-oestradiol levels between the cortisol and sham-implanted treatments in any of the groups. There was a significant difference in the number of subfertile females (<80% embryo viability) when the three treatments were compared. The majority of the females (75%) implanted immediately postspawn (0-4 months) produced subfertile eggs, which was significantly higher than those treated 4-8 (33%) or 8-12 (17%) months postspawn. These results imply that silastic implantation can affect oocyte development, independent of plasma cortisol levels, leading to a reduction in embryo viability.

Morphological and molecular effects of cortisol and ACTH on zebrafish stage I and II follicles

Oogenesis in zebrafish (Danio rerio) is controlled by the hypothalamus-pituitary-gonadal axis and reproductive hormones. In addition, an interference of stress hormones is known with reproductive biology. In the presented work, we aimed to explore the hypothesis that cortisol (Cort) and ACTH may affect early oogenesis in zebrafish, given the presence of the specific receptors for glucocorticoids and ACTH in the zebrafish ovary. Follicles at stages I and II were exposed in vitro to 1  μM Cort and ACTH for 48 h, then ultrastructural and molecular effects were analyzed. The comet assay demonstrated increased tail moments for Cort and ACTH treatment indicative of DNA damage. The mRNA expression of apoptotic genes (bax, bcl-2) was not altered by both treatments, but Cort increased significantly the expression of the ACTH receptor (mc2r). Cort stimulated the presence of the endoplasmic reticulum, predominantly at stage II, while ACTH induced a strong vacuolization. Viability of oocytes was not affected by both treatments and fluorescent staining (monodansylcadaverine/acridine orange) indicated a reduced quantity of autophagosomes for ACTH, and lower presence of nucleic acids in ooplasm for Cort and ACTH. Concluding, different responses were observed for stress hormones on early stages of zebrafish oocytes, which suggest a role for both hormones in the stress-mediated adverse effects on female gametogenesis.

The effect of catch-and-release angling at high water temperatures on behaviour and survival of Atlantic salmon Salmo salar during spawning migration

In this study, behaviour and survival following catch-and-release (C&R) angling was investigated in wild Atlantic salmon Salmo salar (n = 75) angled on sport fishing gear in the River Otra in southern Norway at water temperatures of 16.3-21.1 °C. Salmo salar were tagged externally with radio transmitters and immediately released back into the river to simulate a realistic C&R situation. The majority of S. salar (91%) survived C&R. Most S. salar that were present in the River Otra during the spawning period 3-4 months later were located at known spawning grounds. Downstream movements (median furthest position: 0.5 km, range: 0.1-11.0 km) during the first 4 days after release were recorded for 72% of S. salar, presumably stress-induced fallback associated with C&R. Individuals that fell back spent a median of 15 days before commencing their first upstream movement after release, and 34 days before they returned to or were located above their release site. Mortality appeared to be somewhat elevated at the higher end of the temperature range (14% at 18-21 °C), although sample sizes were low. In conclusion, C&R at water temperatures up to 18 °C had small behavioural consequences and was associated with low mortality (7%). Nevertheless, low levels of mortality occur due to C&R angling and these losses should be accounted for by management authorities in rivers where C&R is practised. Refinement of best practices for C&R may help to reduce mortality, particularly at warmer temperatures.

Evidence for the involvement of dopamine in stress-induced suppression of reproduction in the cichlid fish Oreochromis mossambicus

In the present study, we examined whether stress-induced suppression of reproduction is mediated through the catecholaminergic neurotransmitter dopamine (DA) in the female cichlid fish Oreochromis mossambicus. In the first experiment, application of antibody against tyrosine hydroxylase (TH; a marker for DA) in brain sections revealed the presence of intensely stained TH immunoreactive cells in the preoptic area (POA) and nucleus preopticus (NPO) during the previtellogenic phase. These cells showed weak immunoreactivity during the vitellogenic and prespawning phases concomitant with darkly stained luteinising hormone (LH) immunoreactive content in the proximal pars distalis (PPD) of the pituitary gland and fully ripened follicles (stage V) in the ovary of control fish. However, in fish exposed to aquacultural stressors, TH secreting cells remained intensely stained in POA and NPO regions during the prespawning phase, indicating increased synthetic and secretory activity, which was reflected by a significantly higher DA content compared to controls. Increased DA activity as a result of stress was associated with a decrease in the LH immunoreactive content in the PPD and an absence of stage V follicles in the ovary. In the second experiment, administration of DA caused effects similar to those in stressed fish, whereas DA receptor antagonist domperidone (DOM) treatment significantly increased the LH content in the PPD and the number of stage V follicles in unstressed fish. On the other hand, treatment of stressed fish with DOM resulted in dark accumulations of LH immunoreactive content in the PPD accompanied by the presence of stage V follicles in the ovary. Taken together, these results suggest an additional pathway for the inhibitory effects of stress through dopaminergic neurones along the reproductive axis.

Reproductive and immune effects of chronic corticosterone treatment in male White's treefrogs, Litoria caerulea

Amphibian populations are declining globally. The potential contribution of glucocorticoid hormones to these declines has received little attention, but chronic elevation of glucocorticoids has been linked to a suite of negative outcomes across vertebrate taxa. Recently, chronic environmental stress has been associated with precipitous declines in sperm count and sperm viability in White's treefrogs (Litoria caerulea), but the mechanism remains unknown. In order to determine whether corticosterone is responsible for suppressing reproductive and immune function in this species, we elevated circulating concentrations of corticosterone in 10 male captive-bred frogs via transdermal application for 7 days. We compared sperm count, sperm viability, splenic cell count and circulating leucocyte counts in corticosterone-treated frogs with those in untreated control frogs. Chronic application of exogenous corticosterone led to supraphysiological circulating concentrations of corticosterone, but had no effect on sperm count or viability. However, corticosterone-treated frogs demonstrated a significant decrease in circulating eosinophils, which are immune cells implicated in fighting a variety of pathogens, including extracellular parasites. These findings suggest that although chronic elevation of circulating corticosterone is not necessarily associated with reproductive suppression in this species, it may cause immunosuppression. Thus, chronic glucocorticoid elevations in amphibians might enhance susceptibility to infection with pathogens and parasites, and their potential contributions to global population declines warrant further study.

Population density-dependent hair cortisol concentrations in rhesus monkeys (Macaca mulatta)

Population density is known to influence acute measures of hypothalamic-pituitary-adrenal (HPA) axis activity in a variety of species, including fish, deer, birds, and humans. However, the effects of population density on levels of chronic stress are unknown. Given the fact that exposure to chronically elevated levels of circulating glucocorticoids results in a host of health disparities in animals and humans alike, it is important to understand how population density may impact chronic stress. We assessed hair cortisol concentrations (HCCs), which are reliable indicators of chronic HPA axis activity, in rhesus monkeys (Macaca mulatta) to determine the influence of population density on these values. In Experiment 1, we compared HCCs of monkeys living in high-density (HD; 1 monkey/0.87m(2)) and low-density (LD; 1 monkey/63.37m(2)) environments (N=236 hair samples) and found that HD monkeys exhibited higher hair cortisol across all age categories (infant, juvenile, young adult, adult, and aged) except infancy and aged (F(5)=4.240, p=0.001), for which differences were nearly significant. HD monkeys also received more severe fight wounds than LD monkeys (χ(2)=26.053, p<0.001), though no effects of dominance status emerged. In Experiment 2, we examined how HCCs change with fluctuating population levels across 5 years in the adult LD monkeys (N=155 hair samples) and found that increased population density was significantly positively correlated with HCCs in this semi-naturalistic population (r(s)=0.975, p=0.005). These are the first findings to demonstrate that increased population density is associated with increased chronic, endogenous glucocorticoid exposure in a nonhuman primate species. We discuss the implications of these findings with respect to laboratory research, population ecology, and human epidemiology.

Fish biomarkers for regulatory identification of endocrine disrupting chemicals

Demonstrating chemical-induced adverse effects, endocrine mechanisms/modes of action (MOAs) and their causal link is needed for regulatory identification of endocrine disrupting chemicals (EDCs). This paper addresses critical issues over MOAs and their causal link to changes in endpoints. Vitellogenin (VTG), secondary sex characteristics (SSC), and sex ratio (also an apical endpoint) are indicative of chemicals interfering with EAS (estrogen, androgen and steroidogenesis) pathways. These biomarkers, however, can be changed by non-EAS chemicals, systemic toxicity and the stress response. Examples are shown that proving causal link between MOAs and changes in endpoints may be difficult for regulatory identification of EDCs. The paper concludes that both in vitro and in vivo data are needed to define MOAs for regulatory identification of EDCs. Further development of guidance documents for data interpretation and for defining the level of evidence is needed for regulatory identification of EDCs.

When do we eat? Ingestive behavior, survival, and reproductive success

The neuroendocrinology of ingestive behavior is a topic central to human health, particularly in light of the prevalence of obesity, eating disorders, and diabetes. The study of food intake in laboratory rats and mice has yielded some useful hypotheses, but there are still many gaps in our knowledge. Ingestive behavior is more complex than the consummatory act of eating, and decisions about when and how much to eat usually take place in the context of potential mating partners, competitors, predators, and environmental fluctuations that are not present in the laboratory. We emphasize appetitive behaviors, actions that bring animals in contact with a goal object, precede consummatory behaviors, and provide a window into motivation. Appetitive ingestive behaviors are under the control of neural circuits and neuropeptide systems that control appetitive sex behaviors and differ from those that control consummatory ingestive behaviors. Decreases in the availability of oxidizable metabolic fuels enhance the stimulatory effects of peripheral hormones on appetitive ingestive behavior and the inhibitory effects on appetitive sex behavior, putting a new twist on the notion of leptin, insulin, and ghrelin "resistance." The ratio of hormone concentrations to the availability of oxidizable metabolic fuels may generate a critical signal that schedules conflicting behaviors, e.g., mate searching vs. foraging, food hoarding vs. courtship, and fat accumulation vs. parental care. In species representing every vertebrate taxa and even in some invertebrates, many putative "satiety" or "hunger" hormones function to schedule ingestive behavior in order to optimize reproductive success in environments where energy availability fluctuates.

Metabolic and reproductive effects of relatively low concentrations of beclomethasone dipropionate, a synthetic glucocorticoid, on fathead minnows

Pharmaceuticals present in the aquatic environment could adversely affect aquatic organisms. Synthetic glucocorticoids (GC) are used in large quantities as anti-inflammatory drugs and have been reported to be present in river water. In order to assess the impact of environmental concentrations of GCs, an in vivo experiment was conducted with adult fathead minnows. Fish were exposed to 0.1 μg/L, 1 μg/L, or 10 μg/L beclomethasone dipropionate (BCMD) via a flow-through system over a period of 21 days. Similar duplicate tanks served as control, with no chemical added. There was a concentration-related increase in plasma glucose concentration and a decrease in blood lymphocyte count. Induction of male secondary sexual characters and a decreasing trend in plasma vitellogenin (Vtg) concentrations in female fish were observed with increasing exposure concentration of BCMD. Expression profiles of selected genes (phosphoenolpyruvate carboxykinase - PEPCK, glucocorticoid receptor - GR, and Vtg) in liver also demonstrated concentration-related effects at all three tested concentrations. The results suggest that GCs could cause effects in lower micrograms per liter concentrations that could be environmentally relevant for total GCs present in the environment. Therefore, studies to determine the environmental concentrations of GCs and no effect concentrations are needed to assess if GCs pose a risk to the aquatic environment.

Injuries from non-retention in gillnet fisheries suppress reproductive maturation in escaped fish

Exploitation of fisheries resources has unintended consequences, not only in the bycatch and discard of non-target organisms, but also in damage to targeted fish that are injured by gear but not landed (non-retention). Delayed mortality due to non-retention represents lost reproductive potential in exploited stocks, while not contributing to harvest. Our study examined the physiological mechanisms by which delayed mortality occurs and the extent to which injuries related to disentanglement from commercial gear compromise reproductive success in spawning stocks of Pacific salmon (Oncorhynchus spp.). We found evidence for elevated stress in fish injured via non-retention in gillnet fisheries. Plasma cortisol levels correlated with the severity of disentanglement injury and were elevated in fish that developed infections related to disentanglement injuries. We also analyzed sex steroid concentrations in females (estradiol-17β and 17,20β-dihydroxy-4-pregnen-3-one) to determine whether non-retention impairs reproductive potential in escaped individuals. We demonstrate evidence for delayed or inhibited maturation in fish with disentanglement injuries. These findings have important implications for effective conservation and management of exploited fish stocks and suggest means to improve spawning success in such stocks if retention in commercial fisheries is improved and incidental mortality reduced.

Effects of progesterone on reproduction and embryonic development in the fathead minnow (Pimephales promelas)

High concentrations (375 ng/L) of the steroid hormone progesterone (P4) were measured in snowmelt runoff associated with large livestock-feeding operations in Wisconsin. To gain insight into the potential endocrine-disrupting effects of P4 in fish, experiments were conducted to evaluate the effects of short-term exposure to environmentally relevant concentrations of P4 on reproduction and embryonic development in the fathead minnow (Pimephales promelas). For the reproduction assay, groups of reproductively mature fish were exposed for 21 d to nominal concentrations of 0, 10, 100, and 1,000 ng/L P4 in a flow-through system, and various key reproductive endpoints (e.g., egg number, fertilization success) were quantified throughout the exposure period. The embryonic development assay consisted of incubating fathead minnow eggs in static culture to quantify the effects of P4 on early development and hatching success. Progesterone caused dose-dependent decreases in fecundity and fertility and significantly reduced gonadosomatic index and vitellogenin gene expression in females. There were no effects of P4 on early embryonic development or hatching success. Progesterone may be a significant endocrine-disrupting chemical in fish.

Cortisol and finfish welfare

Previous reviews of stress, and the stress hormone cortisol, in fish have focussed on physiology, due to interest in impacts on aquaculture production. Here, we discuss cortisol in relation to fish welfare. Cortisol is a readily measured component of the primary (neuroendocrine) stress response and is relevant to fish welfare as it affects physiological and brain functions and modifies behaviour. However, we argue that cortisol has little value if welfare is viewed purely from a functional (or behavioural) perspective-the cortisol response itself is a natural, adaptive response and is not predictive of coping as downstream impacts on function and behaviour are dose-, time- and context-dependent and not predictable. Nevertheless, we argue that welfare should be considered in terms of mental health and feelings, and that stress in relation to welfare should be viewed as psychological, rather than physiological. We contend that cortisol can be used (with caution) as a tractable indicator of how fish perceive (and feel about) their environment, psychological stress and feelings in fish. Cortisol responses are directly triggered by the brain and fish studies do indicate cortisol responses to psychological stressors, i.e., those with no direct physicochemical action. We discuss the practicalities of using cortisol to ask the fish themselves how they feel about husbandry practices and the culture environment. Single time point measurements of cortisol are of little value in assessing the stress level of fish as studies need to account for diurnal and seasonal variations, and environmental and genetic factors. Areas in need of greater clarity for the use of cortisol as an indicator of fish feelings are the separation of (physiological) stress from (psychological) distress, the separation of chronic stress from acclimation, and the interactions between feelings, cortisol, mood and behaviour.

Stressed mothers - troubled offspring: a study of behavioural maternal effects in farmed Salmo salar

Mature female Atlantic salmon Salmo salar were given intraperitoneal cortisol implants 1 week prior to stripping to examine the influence of simulated maternal stress on offspring boldness and social dominance. Behavioural tests originally designed to investigate stress responsiveness and coping styles in salmonids (i.e. feeding in isolation, dominance tests and acute confinement) were carried out on the offspring 1·5 years after hatching. In the feeding test, there were no differences between the two treatment groups in total feeding score or number of pellets eaten, but offspring from the cortisol-implanted females made more unsuccessful feeding attempts than offspring from control females. In dominance tests, there was no difference between controls and cortisol-treated fish regarding propensity to become socially dominant. A higher proportion of individuals with bite marks, however, was observed in the cortisol group when compared to controls. Cortisol-treated offspring that gained dominant rank in the dominance tests performed more aggressive acts after stable dominance-subordinate relationships were established compared to control winners. During acute confinement stress, offspring from cortisol-implanted females showed a reduction in the proportion of time they were moving compared to the controls. These results indicate that the maternal endocrine state at spawning affects several aspects of progeny behaviour potentially related to subsequent success and survival in farmed S. salar.

Implantation of cocoa butter reduces egg and hatchling size in Salmo trutta

This study demonstrated that, irrespective of hormone type or dose, administering cocoa butter implants during egg development affected the growth of female brown trout Salmo trutta and reduced the size of their offspring. Cortisol treatment also increased adult mortality. Caution is urged in the use of implants for studies of maternal hormonal influences on adult fishes and their offspring.

The role of female dominance hierarchies in the mating behaviour of mosquitofish

While studies of sexual selection focus primarily on female choice and male-male competition, males should also exert mate choice in order to maximize their reproductive success. We examined male mate choice in mosquitofish, Gambusia holbrooki, with respect to female size and female dominance. We found that the number of mating attempts made by a male was predicted by the dominance rank of females in a group, with dominant females attracting more mating attempts than subordinates. The number of mating attempts made by males was independent of the female size. The observed bias in the number of mating attempts towards dominant females may be driven either by straightforward male mate choice, since dominance and female fecundity are often closely related, or via the dominant females mediating male mating behaviour by restricting their access to subordinate females.

Synthetic glucocorticoids in the environment: first results on their potential impacts on fish

Human pharmaceuticals have been shown to be entering the aquatic environment in quantities that may produce adverse effects to aquatic organisms. This paper investigates the impacts of synthetic glucocorticoids (GCs), which are used in large amounts as anti-inflammatory drugs, on fish. Mammalian cell lines were transiently transfected with trout corticosteroid receptors (GR1, GR2, and MR) and the transactivation abilities of ten of the most prescribed GCs in the UK were measured in vitro. They showed significantly higher activity with GR2 than with GR1. In order to assess any impacts in vivo, adult fathead minnows were exposed to either 1 μg prednisolone/L or 1 μg beclomethasone dipropionate/L for 21 days. Plasma glucose concentrations were increased and leucocytes were reduced significantly in GC-exposed groups compared to the control group. In another experiment, fish were exposed to three different concentrations of Beclomethasone dipropionate and a dose-dependent increase of plasma glucose was found. The results suggest that low concentrations of synthetic GCs present in water could cause adverse effects on fish. Therefore, quantification of GCs in the aquatic environment and the effects of GCs at environmentally relevant concentrations are required in order to determine if GCs pose a threat to wild fish populations.

Exposure of ova to cortisol pre-fertilisation affects subsequent behaviour and physiology of brown trout

Even before fertilisation, exposure of ova to high levels of stress corticosteroids can have significant effects on offspring in a variety of animals. In fish, high levels of cortisol in ovarian fluid can elicit morphological changes and reduce offspring survival. Whether there are other more subtle effects, including behavioural effects, of exposure to cortisol pre-fertilisation in fish is unclear. Here I demonstrate that a brief (3h) exposure of brown trout eggs to a physiologically relevant ( approximately 500 microg l(-)(1)) concentration of cortisol pre-fertilisation resulted in changes to developing offspring. Embryos exposed to cortisol pre-fertilisation displayed elevated oxygen consumption and ammonia excretion rates during development. After hatch, in contrast to the effects of cortisol exposure in juvenile fish, fish exposed to cortisol as eggs were more aggressive than control individuals and responded differently within a maze system. Thus, a transient exposure to corticosteroids in unfertilised eggs results in both physiological and behavioural alterations in fish.

11-deoxycortisol is a corticosteroid hormone in the lamprey

Corticosteroid hormones are critical for controlling metabolism, hydromineral balance, and the stress response in vertebrates. Although corticosteroid hormones have been well characterized in most vertebrate groups, the identity of the earliest vertebrate corticosteroid hormone has remained elusive. Here we provide evidence that 11-deoxycortisol is the corticosteroid hormone in the lamprey, a member of the agnathans that evolved more than 500 million years ago. We used RIA, HPLC, and mass spectrometry analysis to determine that 11-deoxycortisol is the active corticosteroid present in lamprey plasma. We also characterized an 11-deoxycortisol receptor extracted from sea lamprey gill cytosol. The receptor was highly specific for 11-deoxycortisol and exhibited corticosteroid binding characteristics, including DNA binding. Furthermore, we observed that 11-deoxycortisol was regulated by the hypothalamus-pituitary axis and responded to acute stress. 11-deoxycortisol implants reduced sex steroid concentrations and up-regulated gill Na+, K+-ATPase, an enzyme critical for ion balance. We show here that 11-deoxycortisol functioned as both a glucocorticoid and a mineralocorticoid in the lamprey. Our findings indicate that a complex and highly specific corticosteroid signaling pathway evolved at least 500 million years ago with the arrival of the earliest vertebrate.

Effects of the sea louse Lepeophtheirus salmonis on temporal changes in cortisol, sex steroids, growth and reproductive investment in Arctic charr Salvelinus alpinus

Groups of mature (5+ year old) Arctic charr Salvelinus alpinus held in sea water were exposed for 34 days to either a high (mean +/-s.e. 0.15 +/- 0.01 sea lice Lepeophtheirus salmonis g(-1) fish mass) (HI), medium (0.07 +/- 0.00 sea lice g(-1) fish mass) (MI) or no [control (C)] sea-lice infection during early stages of gonad development (June to July). Infection with sea lice resulted in increased plasma cortisol concentrations and this was related to intensity of infection; females tended to have higher cortisol concentrations than males at high infection intensities (HI group: female c. 130 ng ml(-1); male c. 80 ng ml(-1)). Plasma osmolality (C c. 330, MI c. 350 and HI c. 415 mOsm) and chloride concentrations (C c. 135, MI c. 155 and HI c. 190 mM) increased significantly with infection intensity, indicating osmoregulatory problems in infected fish. A strong positive relationship between plasma osmolality and cortisol concentration was recorded. Plasma sex-steroid concentrations were influenced negatively by sea-lice infection, particularly in the HI group, and were inversely related to plasma cortisol concentrations. The most heavily infected fish postponed the initiation of reproductive development until exposed to fresh water and timing of ovulation tended to be delayed in these fish. Growth rate and condition were negatively influenced by sea-lice infection and growth rate was inversely related to plasma cortisol concentrations. Sea-lice infection resulted in mortality among females in the HI group, and the proportion of maturing females was lower in the MI group (46%) than in the controls (85%). Egg production in the MI and HI groups was c. 50 and 30% of the C group. Egg size, embryonic survival and fry mass did not differ across groups. Sea lice influence reproductive development and egg production in S. alpinus, and consequently these parasites may influence populations via sublethal effects on broodfish, affecting growth and condition, and their reproductive output.

Stressors, glucocorticoids and ovarian function in teleosts

The purpose of this overview is to re-examine the postulated direct and indirect actions of glucocorticoids on ovarian function in teleosts. The re-examination is undertaken in light of recent advances in the understanding of the stress response itself, the mode of action of the hypothalamus-pituitary gland-ovarian (HPO) axis, the mechanisms of control of oestrogen-dependent hepatic vitellogenin (VtG) secretion and the apparent roles of corticotrophin-releasing hormone (CRH) and CRH-related factors in the regulation of feeding activity. Many of the results of different studies, particularly whole-animal studies, are conflicting, and little is known as to whether the hormone acts directly on various components of the HPO axis or indirectly by virtue of redirection of energy resources away from ovarian growth to provide a source of metabolic resources for other organ systems involved in the physiological stress response. In vitro studies provide some new insights into the direct actions of glucocorticoid on hepatic VtG synthesis and ovarian follicle steroidogenesis, but even here, in some studies the cellular sites of action of these hormones is not altogether clear. The overview emphasizes the complexity of the stress response, the complexity of the regulation of glucocorticoid-dependent gene expression and the extensive interactive nature of the HPO with other hypothalamus-pituitary gland-peripheral endocrine gland axes, such as the thyroid (HPT), 'somatic' (GH-IGF) and interrenal tissue (HPI) axes.

Stress transcriptomics in fish: a role for genomic cortisol signaling

The physiological responses to stressors, including hormonal profiles and associated tissue responsiveness have been extensively studied in teleosts, but the molecular mechanisms associated with this adaptive response are not well understood. The advent of cDNA microarray technology has transformed the field of functional genomics by revealing global gene expression changes in response to stressor exposures even in non-mammalian vertebrates, including fish. A unifying response in studies related to stressor exposure is activation of the hypothalamus-pituitary-interrenal (HPI) axis in fish, leading to cortisol release into the circulation. Here we will discuss the implications of some of the gene expression changes observed in response to acute stress in fish, while highlighting a role for cortisol in this adaptive stress response. As liver is a key organ for metabolic adjustments to stressors and also is a major target for cortisol action, the genomic studies pertaining to stress and glucocorticoid regulation have focused mainly on this tissue. The studies have identified several genes that are altered transiently after an acute stressor exposure in fish. A number of these stress-responsive genes were also modulated by glucocorticoid receptor activation, suggesting that elevation in cortisol levels during stressor exposure may be a key signal for target tissue molecular programming, essential for stress adaptation. The identification of regulatory gene networks that are stress activated, and modulated by cortisol, both in hepatic and extra-hepatic tissues, including gonads, brain, immune cells and gills, will provide a mechanistic framework to characterize the multifaceted role of cortisol during stress adaptation.

Ovarian steroidogenesis inhibition by constant photothermal conditions is caused by a lack of gonadotropin stimulation in Eurasian perch

In fish, the reasons for the inhibition of reproduction by constant photothermal conditions of rearing are far from clear. In an in vivo experiment, two groups of females reared under natural (4-28 degrees C) or constant photothermal conditions (20-22 degrees C, photoperiod 12/12) were investigated for gonad development, sex-steroids (testosterone-T, 17-beta-estradiol-E2 and 11 Keto-Testosterone-11KT) dynamics and brain aromatase activity in January, February and March. Two days before each sampling date, a group of females reared under constant conditions was injected with HCG (Human Chorionic Gonadotropin: 100 UI/kg) and evaluated for the same parameters. In addition, in vitro ovarian steroidogenesis capacity for each female was determined with or without stimulation by HCG and/or IGF-1 (Insulin-like Growth Factor-1). The results indicate that vitellogenesis stage is the limit ovarian stage never reached in females submitted to constant photothermal conditions. This was associated with gonadogenesis delay and low levels of circulating sex-steroids (T, E2 and 11KT). Nevertheless, HCG injections partly counteracted the plasma steroid deprivation, indicating that ovaries from fish reared under constant photothermal conditions suffer from a lack of gonadotropin stimulation, maybe caused by plasma LH suppression. Such finding was confirmed by the in vitro ovary incubation test. HCG and IGF-1 treatments induced broad testosterone and 17-beta-estradiol elevations and the exposure to constant photothermal conditions, in some cases, decreased that response to HCG. In conclusion, we show that the inhibition of reproductive cycle in Eurasian perch females by constant photothermal conditions of rearing may be related to lower sex-steroid levels and to an inhibition of ovarian regulation by gonadotropins (at least LH), probably stopping gonadogenesis before vitellogenesis stage.