Distribution of cortisol among its free and protein-bound fractions in rainbow trout (Oncorhynchus mykiss): evidence of control by sexual maturation.

1. Total cortisol concentrations did not differ in sexually matured female, male, and immature rainbow trout. 2. The per cent cortisol bound to a corticosteroid binding protein was greater in mature female fish (48.2%) than in mature male (16.0%) and immature fish (19.5%). 3. The mature female fish exhibited a lower percentage of free cortisol (21.8%) compared to mature males (44.8%) and immature fish (43.2%). 4. Parallel aspects of the teleostean cortisol binding-protein and the mammalian counterpart are compared and commented upon.     

Changes in the pituitary metabolism of monoamines (dopamine, norepinephrine, and serotonin) in female and male rainbow trout (Oncorhynchus mykiss) during gonadal recrudescence

The dynamics of the levels and metabolism of dopamine, norepinephrine, and serotonin were studied in pituitaries of male and female rainbow trout at different stages of gonadal development. In female rainbow trout, the turnover of dopamine (calculated using the inhibitor of tyrosine hydroxylase alpha-methyl-p-tyrosine methyl-ester HCl), serotonin metabolism, and norepinephrine levels decreased in the advanced stage of exogenous vitellogenesis with respect to the initial stage. However, data obtained in males did not show changes in either serotonergic or noradrenergic metabolism during the last stages of gonadal development. However, an increase of dopaminergic turnover was noticed in the male fish at the end of spermiation. Finally, pituitary dopaminergic activity was significantly higher in immature (prepubescent stage) than in adult fish.     

Incidence of physical injury of mature male parr in a natural population of brown trout

In a brown trout Salmo trutta population, there was a much higher frequency of injuries among mature male parr than among immature or female parr. The quantitative data are discussed in relation to spawning success and overall fitness.     

Measurement of five androgens in the blood of immature and maturing male rainbow trout, Salmo gairdneri (Richardson)

Antisera for radioimmunoassay (RIA) against testosterone, 11-oxo-testosterone, 11 beta-hydroxytestosterone, 11-oxo-androstenedione, and 11 beta-hydroxyandrostenedione were raised in female rabbits. The RIAs were tested for their suitability for quantification of the steroids after thin layer chromatography of ether extracts from plasma pools of immature and maturing male rainbow trout. Results from control experiments of the RIAs (buffer blanks, sensitivity, cross reactivity, intra- and inter-assay coefficients of variation, accuracy) were all within a normal range. These RIAs should be helpful tools to test the significance of the hypothesis concerning the "interrenal-liver-gonad axis" which has been proposed to account for the high androgen levels in male trout during high reproductive activity.     

The influence of sex and spawning on levels of tryptophan, serotonin and 5-hydroxyindoleacetic acid in the brains of wild brook trout, Salvelinus fontinalis

Levels of tryptophan (TP), serotonin (5-hydroxytryptamine, 5HT) and 5-hydroxyindoleacetic acid (5HIAA) have been determined in the brains of wild brook trout, Salvelinus fontinalis (Mitchill), and brown trout, Salmo trutta L., using high performance liquid chromatography with electrochemical detection. Immediately prior to spawning, adult female brook trout exhibit higher levels of 5HT in the brain than adult males, immature brook trout and immature brown trout. After spawning, the highest levels of TP are found in spent males, which also have higher levels of 5HT in the brain than spent females and immature brook trout. Immature brook trout exhibit higher levels of 5HIAA than prespawning adults. This difference disappears after the spawning season. Serum protein levels and condition factors are lower in spent female brook trout; however, haematocrit values for both sexes remain unchanged after spawning.     

Fish gonadotropin(s). I. Bioassay of salmon gonadotropin(s) in vitro with immature trout gonads.

1. The effect of salmon gonadotropin(s) (SG) on cyclic AMP (cAMP) levels in immature trout gonadal tissue of both sexes was measured by radioimmunoassay. 2. A dose-response line was obtained to SG in gonads of both male and female trout. 3. As little as 0.45 SG units (1 SG unit = 1 mug NIH-LH-S18 in the chick bioassay) significantly increased cAMP formation in the presence of 8 mM theophylline; mammalian LH, FSH, LTH, ACTH, TSH and HCG were inactive. 4. The assay for SG was investigated with respect to time of incubation and two phosphodiesterase inhibitors; some conditions for the cAMP radioimmunoassay (cAMP-RIA) were compared.     

The role of F-series prostaglandins as reproductive priming pheromones in the brown trout

Electrophysiological studies demonstrated that the olfactory epithelium of mature male brown trout Salmo trutta parr was acutely sensitive to F-series prostaglandins (PGFs) PGF_1α and PGF_2α, with detection threshold concentrations of 10⁻¹¹ M. The olfactory epithelium was also sensitive to the PGF metabolite 15-ketoPGF_2α (threshold 10⁻⁸ m), but did not detect a further metabolite, 13,14,-dihydro-15-ketoPGF_2α Immature brown trout did not detect any of the prostaglandins tested. Exposure of mature male brown trout parr to waterborne PGF_1α and PGF_2α (concentration 10⁻⁸ m), resulted in significant increases in levels of expressible milt and the plasma concentrations of 17,20β-dihydroxy-4-pregnen-3-one, testosterone and 11-ketotestosterone. The olfactory epithelium of both immature and mature male brown trout parr was sensitive to the urine and ovarian fluid from ovulated female brown trout. Exposure of mature male brown trout parr to ovarian fluid resulted in an increase in the levels of plasma 17,20β-dihydroxy-4-pregnen-3-one whilst exposure to urine increased the levels of expressible milt. In addition, PGF_2α was found to be present within both the urine and ovarian fluid of mature female brown trout. It is suggested that the F-series prostaglandins have a role as priming pheromones in male brown trout.     

Immunohistochemical Detection of Vitellogenin in Male Brown Trout from Swiss Rivers

The detection of vitellogenin, a yolk precursor protein, may serve as a biomarker for exposure to environmental oestrogens as its induction by xenobiotic oestrogens in the immature and male fish has been reported repeatedly. In the present work, juvenile brown trout were injected with oestradiol (5 g g–1 body weight oestradiol benzoate) in order to assess the induction and organ distribution of vitellogenin by means of immunohistochemistry. In addition, brown trout collected from Swiss rivers were analysed. Vitellogenin was detected in the oestradiol-injected juvenile trout but not in uninjected controls. The presence of vitellogenin was also demonstrated in a male and an immature feral brown trout from one of two locations downstream of three sewage treatment plants. In contrast, no positive staining was found in livers of trout upstream of the respective plants. The results demonstrate the suitability of immunohistochemistry for monitoring feral fish fo r the presence of vitellogenin production.     

Surgical transplantation of sexually immature ovaries in rainbow trout (Oncorhynchus mykiss)

Transplantation of testes between isogenic rainbow trout males has been recently demonstrated. The objective of the present investigation was to determine if ovaries detached from the body wall and removed from the abdominal cavity would reestablish themselves when autografted to an ectopic site. In the first experiment, eleven sexually immature, female rainbow trout were laparotomized midventrally, and the right ovary was removed and transplanted to the abdominal cavity and positioned along the pyloric cecae on the right side. In the second experiment, the ovary was autografted in four animals as in experiment 1 or was transferred to and allografted in four other sexually immature female trout. The animals were examined three months following surgery. At the termination of experiment 1, the autografted ovaries were present in 73% of the animals; the transplanted ovaries were smaller in size than the intact control ovaries. Histological examination did not reveal any necrotic tissue in these transplanted gonads, and oocyte development was not different between the transplanted and the intact ovary within animal. Transplanted ovaries allografted from another female were not found. Taken together, these data support the conclusion that rainbow trout ovaries detached from the body wall can reestablish their blood supply and maintain ovarian development and that female trout appear to reject gonadal tissue from other individuals of their species.     

On remembrance of the abdominal pores in rainbow trout, Salmo gairdneri Richardson, and some other salmonid spp.

Direct connections (abdominal pores) between the peritoneal cavity and the external environment of elasmobranch fishes and some teleost species including the Salmonidae were recognized almost 100 years ago but over this period their existence in these teleost species has been omitted from anatomical texts. In this report, the abdominal pores of rainbow trout, Salmo gairdneri , Atlantic salmon, Salmo salar , and the cisco, Coregonus artedii , were examined in relationship to ip injected particulate material. Both carbon particles and suspensions of the bacterial kidney disease organism were found to be extruded within masses of macrophages and as free particles through the abdominal pores in fish injected ip 72 h previously. The pores were patent in male and female, mature and immature fish. The role and significance of the abdominal pores in rainbow trout in the clearance from the body of material, including material likely to be used for vaccinating fish, is discussed.     

Sex differences of hematological and biochemical parameters in healthy rainbow trout (Salmo gairdneri, R)

A hematological study of the rainbow trout has permitted to establish a sexual difference in the parameters related to it, such as haemoglobin, haematocrit, erythrocyte and leukocyte count. The types of leukocytes were homologated to the human blood. Haemoglobin, haematocrit, erythrocyte sedimentation rate, erythrocyte and leukocyte count values were lower in female than male. The normal values of some biochemistry parameters were equally studied and in some cases they similarly showed a sexual difference. Creatinine, triglycerides, phosphatase alkaline, sodium and globulin values were higher in female than male. Establishing a sexual difference from the biochemical and hematological parameters is possible.     

Effects of acute 17alpha-methyltestosterone,acute 17beta-estradiol,and chronic 17alpha-methyltestosterone on dopamine,norepinephrine and serotonin levels in the pituitary,hypothalamus and telencephalon of rainbow trout (Oncorhynchus mykiss)

This study investigated: (a) the effects of acute 17alpha-methyltestosterone (MT) or 17beta-estradiol (E(2)) administration on norepinephrine (NE), dopamine (DA), serotonin (5-HT), 3,4, dihydroxyphenylacetic acid (DOPAC), and 5-hydroxyindoleacetic acid (5-HIAA) contents in the hypothalamus, telencephalon and pituitary of previtellogenic female rainbow trout Oncorhynchus mykiss, and (b) the effects of chronic MT administration on the levels of these neurotransmitters in these brain regions in immature male rainbow trout. The acute administration of MT induced a significant decrease in pituitary levels of DOPAC as well as in the DOPAC/DA ratio. On the other hand, the acute administration of E(2) induced an increase in pituitary 5-HT levels as well as a decrease in the 5-HIAA/5-HT ratio. In a second experiment, 20 mg MT per kilogram body weight was implanted for 10, 20 or 40 days into sexually immature male rainbow trout. Implanted rainbow trout showed increased testosterone and decreased E(2) levels. In the pituitary, MT induced long-term decreases in NE, DA, DOPAC and 5-HT levels, as well as in the DOPAC/DA ratio. Hypothalamic and telencephalic DA, NE and 5-HT levels were not affected by MT implantation. However, 5-HIAA levels and the 5-HIAA/5-HT ratio were reduced by MT implantation in both brain regions. These results show that chronic treatment with MT exerts both long-term and region-specific effects on NE, DA, and 5-HT contents and metabolism, and thus that this androgen could inhibit pituitary catecholamine and 5-HT synthesis. A possible role for testosterone in the control of pituitary dopaminergic activity and gonadotropin II release is also discussed.     

Histological assessment of early maturation in sea trout (Salmo trutta morpha trutta L.) males in western Pomerania (Poland)

The study was performed to assess the maturation extent of sea trout (Salmo trutta morpha trutta L.) age 0+ males from north‐western Poland on the basis of histological examination. 617 male trout were collected from seven streams that had been stocked with swimming sea trout fry and classified into groups according to maturity stages: 64% were immature (Class I) in the first year of life; 17% remained in Class II with unfinished spermatogenesis. Mature male sea trout made up about 19% of the population; 72.6% thereof underwent incomplete maturation and 47.8% did not spermiate.     

Vitellogenin levels in male and female rainbow trout (Salmo gairdneri Richardson) at various stages of the reproductive cycle

The immunoassayable vitellogenin (VTG) in plasma from male rainbow trout had the same molecular weight as authentic VTG from female fish. The VTG level in male trout was low (usually nanograms, occasionally up to a few micrograms, per ml) and did not correlate with the stage of sexual maturity. The plasma VTG level of female trout that were two years from first spawning was 200-fold higher than males of the same strain and age. The plasma VTG level of female rainbow trout rose approximately a million-fold during the two or three years required to attain sexual maturity.     

Morphological ontogeny of the gonad of three plectropomid species through sex differentiation and transition

The gonadal ontogeny through sex differentiation and transition of three protogynous coral trout species, Plectropomus leopardus , P. maculatus and P. laevis was described, based on anatomical and germinal differences along the length of the reproductive tract. Gonads of immature and mature females, sex changing individuals (transitionals) and males were examined. Specific anatomical features that were compared between sexual phases included the presence and structure of sperm sinuses, gonadal musculature and germinal cell types. All three coral trout species first differentiated as an immature female. The sexual pattern of P. leopardus and P. maculatus was concluded to be diandric protogynous hermaphroditism (males were derived from the juvenile phase as well as through sex change of mature females). Plectropomus laevis was found to be monandric as males were only derived through sex change in mature females. Structural changes did not occur concomitantly with the germinal changes associated with sex change in these Plectropomus species, which is atypical for protogynous species described to date. Precursory sperm sinuses in the dorso-medial region of the gonad were present, although non-functional, in a proportion of immature and mature females of all three species. These proportions, however, varied between species depending on the sexual pattern. The structural and germinal changes observed were hypothesized as anatomical adaptations that aid in minimizing time spent in the (non-reproductive) sexual transition phase and maximizing flexibility in male development in the diandric species.     

Differences in Mating Propensity Between Immature Female Color Morphs in the Damselfly Ischnura elegans (Insecta: Odonata)

Female-limited color polymorphisms occur in a variety of animal taxa where excessive male sexual harassment may explain the coexistence of multiple female color morphs. In the color polymorphic damselfly Ischnura elegans, mature and immature female color morphs coexist at the mating site where males are in search for suitable mating partners. Here, we study male preference and female mating propensity for the two immature female morphs. As would be expected, compared to mature morphs, both immature female morphs mate much less. Within immature females, one morph consistently mates more frequently compared to the other morph, a pattern that is similar for the ontogenetically corresponding mature female morphs. Preference experiments with the two differently colored immature female morphs, however, did not indicate male mate preference for either morph. Low mating frequencies of immature females at natural sites in combination with relatively high attractiveness of immature models in terms of male preference indicate that female behavior influences female mating success.     

Sacciform cells in the epidermis of the brown trout,Salmo trutta,and the Arctic char,Salvetinus alpinus

Summary Sacciform cells containing an acidophilic, proteinaceous secretion, were identified in the epidermis of the brown trout and Arctic char. This cell type increased in number during the chronic stages of infestation by the ectoparasitic flagellate, Ichthyobodo sp., in immature brown trout, and decreased during sexual maturation in male brown trout and char. It is suggested that the salmonid sacciform cell produces a secretion which protects the fish against infestation or damage by skin parasites.     

Sex-Specific Aggression and Antipredator Behaviour in Young Brown Trout

Sex differences in adult behaviour are often interpreted as consequences of sexual selection and/or different reproductive roles in males and females. Sex-specific juvenile behaviour, however, has received less attention. Adult brown trout males are more aggressive than females during spawning and juvenile aggression may be genetically correlated with adult aggression in fish. We therefore tested the prediction that immature brown trout males are more aggressive and bolder than immature females. Because previous work has suggested that precocious maturation increases dominance in salmonids, we included precocious males in the study to test the prediction that early sexual maturation increase male aggression and boldness. Aggression and dominance relations were estimated in dyadic contests, whereas boldness was measured as a response to simulated predation risk using a model heron. Independent of maturity state, males initiated more than twice as many agonistic interactions as females in intersexual contests. However, males were not significantly more likely to win these contests than females. The response to a first predator attack did not differ between sex categories, but males reacted less to a second predator attack than females. Sexual maturity did not affect the antipredator response in males. Since there is no evidence from field studies that stream-living immature male and female salmonids differ in growth rate, it appears unlikely that the sex differences demonstrated are behavioural consequences of sex-specific investment in growth. It seems more likely that sex-specific behaviour arises as a correlated response to sexually selected gene actions promoting differential behaviour in adult males and females during reproduction. Alternatively, sex differences may develop gradually during juvenile life, because a gradual developmental program should be less costly than a sudden behavioural change at the onset of sexual maturity.     

Body composition and organ weights of rainbow trout,Salmo gairdneri*

The objectives of the study were to determine the chemical constituents of rainbow trout (Salmo gairdneri) during the first 14 months of life, to study the effects of starvation on the body composition of trout, and to measure organ weights during the first 14 months of life. Body fat and protein content as a percentage of body weight increased with age, the water content declined, and the ash content remained constant during the first 14 months of life. There were no significant differences in body composition between immature male and female rainbow trout. Total body ions as a proportion of ash content decreased until the 10th month and then began to increase. During starvation, fat was used as the primary source of energy while water and ash content increased and protein content remained constant as a percentage of body weight. The gall bladder, liver, and air bladder remained relatively constant as a percentage of body weight during the first year of life. As body weight increased, the relative weight of brain, heart, and digestive system decreased while the gonad and spleen weight increased.     

Testicular development in the sea trout (Salmo trutta morpha trutta L.) after sex differentiation, with a reference to precocious maturation

Testicular development was followed in juvenile sea trout (Salmo trutta morpha trutta L.) stocked in a river near Szczecin, Poland in 1992. Fish age was between 3 and 6.5 months post‐hatch. Fish were sampled monthly. Sex‐dependent differences in gonad structure and timing of their differentiation were observed after dissection under light microscope. In 3‐month‐old fry, when female gonads were differentiating (morphologically and cytologically), gonads of potential males remained undifferentiated. Development of a gonad into a male was primarily indicated by the formation of seminiferous tubules (lobules). In the sea trout under study, the lobules formed between the fourth and fifth month post‐hatch (July–August) (fork length >5.6 cm). There were no significant differences in body fork length between fish with and without lobules, although mean length of the former was higher. Early spermatogenesis began once the type B spermatogonia appeared. The timing of their appearance differed widely among individuals. Type B spermatogonia were found for the first time in a 5‐month‐old male (late August). Spermatocytes and cells of subsequent stages appeared in an incompletely matured 6.5‐month‐old male as ‘attempted spermatogenesis’ (fork length = 8.8 cm). Most examined males remained immature, their germ cells not having passed the type A spermatogonium level. In 6.5‐month‐old alevins, no significant differences in fish size between individuals beginning spermatogenesis (stage II) and those at stage I were detected, although those at stage II were longer. As the male gonad structures were forming, the quantitative gonad parameters were gradually increasing, even when referring to the unit area; only the gonocyte size gradually decreased. Generally, each observed monthly or bimonthly difference was statistically significant (P < 0.05).