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1.
Steroid hormone profiles accompanying sexual maturation in captive milkfish are described. There were no significant differences in levels of serum estradiol 17- (E2) and testosterone (T) between immature male and female fish. Mean E2 levels rose from 0.54±0.11 ng/ml in immature females (Stage 1) to 4.53±1.16 ng/ml in vitellogenic females (Stage 5), while T levels increased from 2.06±0.28 ng/ml to 38.4±9.26 ng/ml. E2 and T levels were positively correlated to GSI and oocyte diameter. In males, serum T levels increased from 2.5±0.40 ng/ml in immature males to 27.73±5.02 ng/ml in spermiating males. A significantly higher T level was found in males with thick and scantly milt (spermiation index, SPI, 2) compared to males with scanty milt (SPI, 1) or males with copious, fluid milt (SPI, 3).Serum levels of E2 and T, and the GSI in females rose significantly during the breeding season (April–June 1983). The levels of both steroids dropped below 1 ng/ml in spent females sampled in succeeding months. In immature males, T levels ranged from 1.11 ng/ml to 2.78 ng/ml and rose significantly to 21.52±8.38 ng/ml during the breeding season when GSI peaked. Serum T levels dropped to around 10 ng/ml in the succeeding months when only spent or regressed males were sampled.  相似文献   

2.
The annual reproductive cycle of walleye (Stizostedion vitreum) was characterized by documenting changes in gonadal development and serum levels of estradiol-17β (E2), testosterone (T), 17α,20β-dihydroxy-4-pregnen-3-one (17,20-P), and 11-ketotestosterone (11-KT) in wild fish captured from upper midwestern lakes and rivers throughout the year. Fish from the populations used in this study spawn annually in early- to mid-April. Walleye showed group synchronous ovarian development with exogenous vitellogenesis beginning in autumn. Oocyte diameters increased rapidly from ∼ 200 μm in October to ∼ 1,000 μm in November, and reached a maximum of 1,500 μm just prior to spawning. Changes in gonadosomatic indices (GSIs) paralleled changes in oocyte diameters. Serum E2 levels in females increased rapidly from low values in October (< 0.1 ng ml−1) to peak levels of 3.7 ng ml−1 in November, coinciding with the period of the most rapid ovarian growth. Subsequently, E2 levels decreased from December through spawning. Serum T levels exhibited a bimodal pattern, increasing to 1.6 ng ml−1 in November, and peaking again at 3.3 ng ml−1 just prior to spawning. We detected 11-KT in the serum of some females at concentrations up to 5.6 ng ml−1, but no seasonal pattern was apparent. In this study (unlike our results in a related study) 17,20-P was not detected. In males, differentiation of spermatogonia began in late August, and by January the testes were filled (> 95% of germ cells) with spermatozoa. Mature spermatozoa could be expressed from males from January through April. GSIs ranged from 0.2% (post-spawn) to 3.2% (pre-spawn). Serum T levels rose from undetectable levels in post-spawn males to 1.6 ng ml−1 by November, remained elevated throughout the winter, and peaked at 2.8 ng ml−1 I prior to spawning. Levels of 11-KT in males remained low (< 10 ng ml−1, from post-spawning through January, then increased significantly by March and peaked just prior to spawning at 39.7 ng ml−1. Our results indicate that vitellogenesis and spermatogenesis are complete or nearly so, in walleye by early winter, and suggest that it may be possible to induce spawning in this species several months prior to the normal spawning season by subjecting fish to relatively simple environmental and hormonal treatments.  相似文献   

3.
To elucidate the role of gonadotropin-releasing hormone (GnRH) in gonadal maturation in wild female Japanese flounder Paralichthys olivaceus, we monitored changes in the levels of seabream GnRH (sbGnRH) in the olfactory bulb, telencephalon, hypothalamus, and pituitary during ovarian development together with changes in plasma levels of testosterone (T), estradiol-17β (E2), and 17α, 20β-dihydroxy-4-pregnen-3-one (DHP). Fish were caught offshore of the northern mainland of Japan in the Pacific Ocean at 3- to 4-week intervals between April and September by gill net. The netted fish were categorized into six groups based on ovarian stages: previtellogenic (April–early May), early yolk (April–late May), late yolk (late May–June), early spawning (June–August), late spawning (September), and termination (September) stages. The gonadosomatic index significantly increased from the previtellogenic to early spawning stages and decreased thereafter. In the olfactory bulb, no significant differences were observed in sbGnRH levels among the developmental stages. In contrast, sbGnRH levels in the telencephalon and hypothalamus were very high in the previtellogenic stage, lower in the early spawning stage, and relatively high in latter stages. sbGnRH levels in the pituitary were high in the previtellogenic stage and low in the early spawning stage. In addition, the relatively high levels of pituitary sbGnRH were found together with high plasma T, E2, and DHP levels in fish in the late yolk stage. These results indicate that sbGnRH in the telencephalon, hypothalamus, and pituitary is involved in ovarian maturation and that sbGnRH may play an important role in the initiation of ovarian recrudescence in wild Japanese flounder.  相似文献   

4.
In this study, developmental changes in the steroidogenic capacity of testicular fragments and isolated ovarian follicles of a hybrid sturgeon, Bester, at a variety stage of developments were examined. Testicular fragments or isolated ovarian follicles were incubated in L-15 medium in the presence or absence of different concentrations of five preparations; forskolin, human chorionic gonadotropin (HCG), pregnenolone (P5), 17-hydroxyprogesterone (17OHP) and testosterone (T) for 18 h at 15 °C. After incubation, concentrations of 11-ketotestosterone (11 KT) (testis) and, 17-estradiol (E2) (ovarian follicles) and 17,20-dihydroxy-4-pregnen-3-one (DHP) (testis and ovarian follicles) were measured. 11KT was detected in the media following incubation with P5, 17OHP and T. Its concentration was higher during late spermatogenesis and prespermiation and lower at the degeneration stage. Both P5 and 17OHP were converted to DHP during the prespermiation stage. Forskolin had little stimulatory effect on the synthesis of 11KT and DHP and HCG did not induce the production of these steroids.E2 was detected in the medium following incubation of follicles with P5, 17OHP and T at all stages of oocyte development. The concentration of E2 in the medium increased during vitellogenesis with the peak production occurring at the tertiary yolk stage. In contrast, the potencies of follicles to produce steroids shifted to the production of DHP during migratory nucleus stage. Forskolin and HCG had little effect on the synthesis of E2 and DHP. These results demonstrated that the failure of spontaneous spermiation or ovulation is not due to the insufficient synthesis of DHP, but may due to the lack of availability of precursors.  相似文献   

5.
Triploid fish have under-developed gonads due to altered reproductive endocrinology. Triploids of Indian catfish (H. fossilis) showed significantly reduced plasma levels of gonadotropin (GtH-II), testosterone (T) and estradiol-17 (E2) than that of diploids throughout the year, except for the resting phase, irrespective of sex. Plasma levels of GtH-II were significantly different (p<0.001) between diploid and triploid fish during preparatory, prespawning and spawning phase. The plasma testosterone contents in triploids were significantly less (p<0.001) than that of diploids, except during the resting phase. Triploid females showed very low titres of estradiol-17 (<1 ng ml–1) throughout the annual reproductive cycle in contrast to highly fluctuating levels in diploid females. Thus, this study for the first time provides information on reduced levels of GtH-II and sex steroids in plasma of male triploid fish and additional information on species-specific alteration of sex hormones in female triploids.  相似文献   

6.
The objective of the present study was to investigate the in vivo effects of different doses of 17-estradiol (E2) and testosterone (T) on the levels of plasma and pituitary gonadotropin II (GTH II) in 2-year-old black porgy, Acanthopagrus schlegeli, during the spawning season. Male fish were distributed among 7 groups (n = 49), control, E2or T (with 3 doses, 2.4 ng, 72 ng and 2.2 g g–1 body weight). Fish were injected with the respective vehicle or different doses of E2 or T on days 1 and 14. Plasma E2 levels were significantly increased in the 72 ng E2 group on days 8 and 14. Plasma vitellogenin levels were significantly higher in the 72 ng E2 group on days 14 and 20, and 2.2 g E2 group on days 8, 14 and 20 than those in the control group. Plasma GTH II concentrations were significantly higher in the 2.2 g E2 group than in the control and other E2groups on days 8, 14 and 20. Pituitary GTH II contents was significantly higher in the 7.2 ng E2 group compared to the control and other E2groups on day 20. Plasma GTH II concentrations were similar in the control and all the T groups on days 8, 14 and 20. None of the doses of T treatment stimulated pituitary GTH II content on day 20, although plasma vitellogenin levels were elevated. It is concluded that GTH II synthesis and secretion in black porgy is stimulated by an estrogen-specific effect.  相似文献   

7.
The relationship between plasma and ovarian levels of gonadal steroids was examined in two New Zealand fish species with multiple spawning cycles of differing length. Snapper (Pagrus auratus) have a daily cycle of oocyte development, ovulation and spawning, whereas demoiselles (Chromis dispilus) spawn over 2–3 days during a repeat spawning cycle of 7–9 days. Ovarian and plasma levels of the gonadal steroids 17β-estradiol (E2), testosterone (T), 17-hydroxyprogesterone (17P) and 17,20β-dihydroxy-4-pregnen-3-one (17,20βP) were measured in reproductively active fish captured from the wild. Ovarian levels of E2, T and 17P changed in relation to spawning cycle and gonad stage in both snapper and demoiselles. E2 and T levels were detectable at all times, but highest during vitellogenesis in both species. Cyclic changes of 17P occurred in both species, and levels appeared to depend on the rate of conversion of 17P to other hormones. No changes in ovarian levels of 17,20βP were detected in relation to stage of the spawning cycle in snapper; however, ovarian levels of 17,20βP were highest in demoiselles before spawning when fish undergoing final oocyte maturation predominated. Plasma levels of E2 and T were strongly correlated with ovarian concentrations (r=0.850 and r=0.819 for E2 and T respectively) in demoiselles but there was poor correlation between ovarian and plasma levels of 17P and 17,20βP (r=0.004 and 0.273 respectively), or between ovarian and plasma levels of E2, T, 17P or 17,20βP of snapper (r=0.135, 0.277, 0.131 and 0.279). The poor correlation between plasma and ovarian levels of some steroid hormones suggests that plasma concentrations of steroids may not adequately reflect the reproductive status of the fish during short-term cyclic ovarian changes. It is suggested that this disparity is likely to be most marked in species with ovulatory periodicity of short duration.  相似文献   

8.
The role of gonadotropin (GTH) in the reproduction of the Japanese flounder, Paralichthys olivaceus, was studied by assessing the changes in the apparent activity of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) in the pituitary gland during gonadal maturation by immunohistochemical analyses. Corresponding changes in plasma levels of testosterone (T), estradiol-17β (E2), and 17α,20β-dihydroxy-4–pregnen-3-one (DHP) were also studied. Reared fish at the early spawning to termination stages were sampled from May to August and wild fish at the previtellogenic to termination stages were caught at 3- to 4-week intervals between April and September offshore from the northern mainland of Japan by gill nets. The gonadosomatic index of the reared fish decreased from the early spawning stage to the termination stage, while that of the wild fish increased significantly from the previtellogenic stage to the early spawning stage and decreased thereafter. In the reared fish, the immunostaining intensities of FSH and LH were high during the spawning period, accompanied by high plasma levels of T, E2, and DHP. In the wild fish, the immunostaining intensities of FSH and LH were low during the previtellogenic stage but increased during the maturing and spawning stages. These results indicate that both FSH and LH are likely associated with oocyte maturation in the Japanese flounder.  相似文献   

9.
Two year old black porgy (Acanthopagrus schlegeli) fed a diet containing 4.0 mg kg–1 of estradiol-17 (E2) for 5 months had significantly lower GSI than the control group during the spawning season. E2 suppressed testicular development, spermiation and plasma testosterone (T) and 11-ketotestosterone (11-KT) and stimulated ovarian development, vitellogenesis and sex reversal. Spermiation in the control group occurred in January and February with the concentrations of 1.08–1.36 × 1010 sperm ml–1 of milt. Higher plasma T and 11-KT, but lower E2 levels were detected in the spermiating fish (control group). Higher plasma E2 levels were detected in the sex reversing black porgy during the pre-spawning season. A sharp rise in plasma 11-KT and a drop in T levels were detected in spermiating fish (control group) from January to February. Plasma 11-KT levels correlated with the testicular development and spermiation. The data suggest that E2 plays an important role in controlling the sex reversal of black porgy.to whom correspondence should be addressed.  相似文献   

10.
Gonad and plasma samples were taken from blue cod captured throughout the reproductive cycle, gonad condition was assessed, and plasma levels of 17-hydroxyprogesterone (17OHP), 17,20-dihydroxy-4-pregnen-3-one (17,20P), testosterone (T), 17-estradiol (E2) and estrone (E1) were measured by radioimmunoassay. It was confirmed that spawning occurred over an extended period in late winter and spring, with individual fish being involved in multiple spawning events. Plasma levels of T were bimodal in both sexes with peaks (maximum of 6.0 ng.ml–1) occurring 2 months prior to, and also during the early part of the spawning period. 17,20P was elevated in males (2.1 ng.ml–1) in mid-spermatogenesis coinciding with the first T peak (4.9 ng.m.–1). 17,20P was detectable but not significantly elevated (0.6–1.2 ng.ml–1) at any sample time in females. E2 was elevated in mature females (1.0 ng.ml–1) early in the spawning period but remained at assay detection limits (0.3 ng.ml–1) at all other sample times. Neither 17OHP nor E1 were detectable in the plasma of either sex. It is suggested that bimodal increases in sex steroids prior to spawning may be a feature of species with rapid recrudescence.  相似文献   

11.
Blood and ovarian samples were collected at intervals of 4h prior to spawning time from medaka (Oryzias latipes) that were maturationally synchronized with artificial photoperiod (14h light: 10h dark). Plasma estradiol-17β (E2) levels increased rapidly from 16h before spawning and peaked at 8h before spawning. Follicle-enclosed oocytes (ovarian follicles) at different stages of development were isolated from the ovaries and used to study the in vitro effects of thyroid hormone (triiodothyronine; T3) on pregnant mare serum gonadotropin (GTH)-induced E2 production. GTH at a concentration of 100 IU/ml stimulated E2 production by ovarian follicles collected between 32 and 16h before spawning. At 32h before spawning, T3 (5 ng/ml) administered along with GTH (100 IU/ml) resulted in a 3.5 fold increase in E2 production, compared with GTH administered alone. These results suggest that T3 can act on ovarian follicles directly to modulate GTH-stimulated E2 production in the medaka.  相似文献   

12.
Plasma estradiol-17 (E2), testosterone (T), 17,20-dihydroxy-4-pregnen-3-one (DHP) and 17,20,21-tri-hydroxy-4-pregnen-3-one (20-S) levels were measured by radioimmunoassay (RIA) in white perch (Morone americana) and white bass (M. chrysops) that were induced to undergo final oocyte maturation (FOM) with human chorionic gonadotropin (hCG). Plasma DHP levels increased in females of both species in association with oocyte germinal vesicle migration (GVM) and germinal vesicle breakdown (GVBD) and decreased thereafter. Plasma 20-S levels also increased with oocyte GVM in white bass, but were several-fold lower than DHP levels. Circulating E2 and T levels were greatest during GVM and GVBD in both species and decreased to low levels during oocyte hydration and ovulation. Follicles from white perch and white bass which received a priming injection of hCG in vivo, produced both DHP and 20-S in vitro after exposure to hCG and their oocytes underwent GVBD. Ovarian incubates from unprimed fish of either species produced only E2 and T and their oocytes did not complete GVBD. Oocytes from unprimed bass, but not perch, matured when follicles were exposed to hCG in vitro. Both trilostane and cycloheximide blocked in vitro production of DHP and 20-S and oocyte GVBD by white perch follices. DHP and 20-S were equipotent inducers of FOM in the GVBD bioassay. None of several other structurally-related steroids tested were effective within a physiological range of concentrations. These results indicate a role for DHP and 20-S in the control of FOM in white perch and white bass.  相似文献   

13.
The annual profile of plasma vitellogenin (VTG) and 17ß-estradiol (E2) levels, as well as gonadal development and spawning characteristics were investigated in captive female sea bass (Dicentrarchus labrax). Endocrine and gonadal changes were studied in fish reared under natural conditions or exposed to manipulated photothermal cycles. In natural conditions of photoperiod and temperature, sea bass spawned from February through March (East coast of Spain, 40°N 0°E). One or two months of constant long-days (15L/9D) in a constant short-day photoperiod regime (9L/15D) all-year-round, given early in the year (March and March–April), advanced spawning by 3 months. The same treatment applied later in the year (September–October) delayed spawning by 1 month, compared to controls.In all groups, changes in plasma VTG levels were correlated with E2 levels, oocyte growth and spawning time. In control females, VTG was low (<100 ng ml-1) during the summer, until its first surge in plasma 4 months before the beginning of spawning. The VTG (3.1 ± 0.3 mg ml-1) and E2 (4.1 ± 0.5 ng ml-1) levels showed a single annual peak during late vitellogenesis, the time of the highest proportion of vitellogenic oocytes in the ovary. Constant high levels of VTG (1–1.4 mg ml-1) and E2 (1.6–1.9ng ml-1) were maintained during the entire spawning time, together with the presence of vitellogenic oocytes, suggesting the existence of several waves of oocyte growth in the ovary and thus, several spawns per female. Endocrine profiles and oocyte development in fish exposed to constant photoperiods were similar to controls, but were shifted in time in relation to the displacement of the spawning time. In the fish showing advanced spawns, the duration of the gametogenic proces was compressed when compared to controls. The differences observed in the evolution of the reproductive-related factors in the advanced groups, which were exposed to a reduction in temperature to 15°C, suggest an influence of the temperature in the early stages of the reproductive cycle in sea bass.  相似文献   

14.
This investigation examines the influence of implants containing 11-ketotestosterone (11KT), 17-estradiol (E2), and 3,5,3-triiodo-l-thyronine (T3) on astaxanthin metabolism in sexually immature individually tagged Arctic charr. The fish (initial average weight 427 g) were maintained in freshwater for 40 days, and weekly implanted intraperitoneally with oil-based injections containing either 11 KT, E2 or T3 at levels of 0.1, 1.0 and 0.1 mg (100 g body weight (BW))–1, respectively. The control fish were given the oil medium alone (0.2 ml 100 g BW–1). The diet contained ca. 50 mg astaxanthin kg–1. Carotenoid composition was monitored in plasma, fillet, liver and skin, and 11 KT, E2 and testosterone (T) levels in plasma. All hormone treatments reduced plasma T compared to the control. E2-treated fish had a higher (p<0.05) hepatosomatic index (HSI) than the other treatments. Hormone treatment did not influence gonadosomatic index (GSI). T3 administration induced a silvery skin appearance. The fillet and plasma carotenoid content decreased during the experiment. 11 KT implantation reduced astaxanthin and idoxanthin concentrations of plasma and fillets, and increased the amount in liver and skin, compared to the other treatments. The relative proportion of astaxanthin to idoxanthin was higher in the control fish and T3 implanted fish, than in fish implanted with 11 KT or E2 (p<0.05). Fish treated with E2 had the highest skin carotenoid concentration. Male fish had significantly higher carotenoid content in plasma, fillet and skin than female fish. This study reveals that sex hormones affect carotenoid metabolism and partitioning among body compartments of Arctic charr, effects differently displayed by the sexes.  相似文献   

15.
To determine steroid profiles in immature and maturing female eels from the wild, non-migratory and migratory New Zealand longfinned (Anguilla dieffenbachii) and shortfinned (A. australis) eels were caught and blood and ovarian samples collected. Plasma steroid levels were determined and related to the developmental stage of the ovary. Ovaries of non-migrants contained oogonia and previtellogenic oocytes. Vitellogenic oocytes were never observed in these groups, but instead were very common among migrants (up to 88% of oocytes). Concentrations of both androgens (androstenedione (AD), testosterone (T)) and estradiol-17 (E2) were higher in migrants than in non-migrants. Among migrants, T levels were higher in shortfins (2.27 ± 0.14 ng ml–1) than in longfins (0.82 ± 0.10 ng ml–1), whereas E2 levels were higher in longfins (mean 2.46 ng ml–1) than in shortfins. Levels of sex steroids were generally low in non-migrants. In contrast, plasma levels of 17-hydroxyprogesterone were significantly higher in non-migrants than in migrants. Similarly, cortisol levels were higher in non-migrating than in migrating shortfinned, but not longfinned, females. 17,20-Dihydroxy-4-pregnen-3-one, the putative maturation-inducing steroid in anguillids, was near minimum-detectable levels for all animals examined. Surprisingly, very high levels of 11-ketotestosterone (KT) were found in migrants, averaging nearly 3 ng ml–1 in longfins and over 20 ng ml–1 in shortfins. The identity of KT and several 5-reduced androgens was confirmed using gas chromatography - mass spectrometry. The function of KT in females is not known, but we suggest that this steroid hormone may play a role in preparing maturing animals for their spawning migration.  相似文献   

16.
The in vitro basal and salmon gonadotropin (sGTH)-stimulated steroidogenic capacity of rainbow trout follicles was examined at four stages [early (EV)-, mid (MV)- and peak-vitellogenic (PV), and pre-ovulatory, post-vitellogenic (PO)] of gonadal recrudescence using radioimmunoassays (RIAs) to measure 17-estradiol (E2) and testosterone (T) production. In addition, follicles were incubated in the presence of [3H]pregnenolone ([3H]P5) and the radiolabelled steroid metabolites produced were separated using high performance liquid chromatography (HPLC). Peak basal and sGTH-stimulated E2 and T production was found in PV stage follicles and lowest in PO stage follicles, and there were marked differences in the HPLC profiles of steroid metabolites. For EV stage follicles the major metabolite eluted as a peak that co-eluted with the androstenedione (A4) and 17-hydroxyprogesterone (17-OHP) standards. A smaller peak that co-eluted with 11-hydroxyandrostenedione (11-OHA4) and very small peaks co-eluting with 20-dihydroprogesterone (20-DHP) and E2 were also seen. MV and PV stage follicles produced predominantly E2, together with a small combined A4 + 17-DHP peak, traces of 11-OHA4 and two peaks that did not co-elute with any of the reference standards. The PO stage follicles produced only 17, 20-dihydroxy-4-pregnene-3-one (17,20-P).In addition, the effects of cortisol and triiodothyronine (T3) on steroidogeneis were investigated in PV and PO stage ovarian follicles. For PV stage follicles, cortisol at 100 ng ml–1 in the incubation medium significantly suppressed both basal and sGtH- stimulated T and E2 production relative to control treatments. T3 at 10 ng ml–1 in the medium had no significant effect on either basal or sGtH-stimulated T or E2 production compared to the controls, nor did it have any beneficial effect over the suppressive effect of cortisol. PO phase follicles taken 1 to 2 weeks prior to anticipated spawning had very low E2 and T production, and there was no effect of cortisol or T3, alone or in combination, on E2 or T production. For PV stage follicles incubated in the presence of [3H]P5, cortisol suppressed T and E2 production, but did not block the steroid pathway at any specific level; T3 had no apparent affect on the metabolism of [3H]P5. The PO stage follicles produced little or no E2; the major metabolite was 17,20-P. Cortisol and T3 had no apparent effect on either basal or sGtH-stimulated 17,20-P production by the follicles at this stage of maturation.  相似文献   

17.
The seasonal changes in hepatosomatic index (HSI), gonadosomatic index (GSI) and plasma estradiol‐17β (E2) level in female rabbit fish (Siganus guttatus) were investigated. The relationship between plasma E2 levels with these indices and ovarian growth was also evaluated. Each month, at least 10 female broodfish were sacrificed to collect liver, ovary and blood for HSI, GSI and plasma E2, respectively. GSI and HSI were calculated as percentage (%) of relative weight of gonad and liver to total body weight, respectively. Plasma E2 level was measured using enzyme‐linked immunosorbent assay method (ELISA). Ovaries were cut and stained for histological observation. The results included seasonal changes in plasma E2 levels, stages of ovarian development, GSI and HSI. The highest level of E2 was observed in June (1,445.62 pg/ml) and during vitellogenesis (2,305 pg/ml). GSI and HSI values significant fluctuated monthly. The highest HSI and GSI were 1.72% in May and 3.58% in June, respectively. The pattern of plasma E2 levels showed a relationship with GSI and different stages of ovarian development. HSI was associated with ovarian stages. During vitellogenesis, the highest value (1.9%) of HSI was observed. Histological sections showed that rabbit fish is a multiple spawner. These results contribute to further understanding of female rabbit fish reproductive biology in captivity. Important reproductive parameters such as HSI, GSI and E2 can be used to indicate maturation status of this fish species.  相似文献   

18.
Plasma levels of L-thyroxine (T4) and 3,5,3-triiodo-L-thyronine (T3) and the percentage of plasma T4 and T3 present in the free (dialyzable) form (%FT4 and %FT3) were measured in 16 species (11 families) of tropical marine teleosts from an inshore Barbados reef. Mean plasma T4 varied from 0.2 ng/ml to 42 ng/ml; mean plasma T3 varied from < 0.2 ng/ml to 50 ng/ml. The highest T4 and T3 levels were recorded in parrot-fish and the lowest levels in filefish. The %oFT4 and %FT3 varied from 0.05–3.41%. Estimated levels of plasma free T4 and free T3 levels ranged from 0.4–466 pg/ml. The extremely wide inter- and intra-species ranges in levels of free T4 and T3 do not support a previous suggestion, based on temperate freshwater salmonid species, that free T4 and T3 levels in fish may fall within a relatively range narrow comparable to that of homeothermic vertebrates.  相似文献   

19.
The ingestion of an inert feed as a sole food source was investigated in larval silver sea bream (Sparus sarba) fed an alginate-based microparticulate diet. Using the auto-fluorescent properties of pigments associated with the alginate base, ingestion and gut content were investigated over a 6 h experimental period in fed and unfed larvae. By extracting and measuring chlorophyll a (Chl a) and phaeopigment content of feeding larval fish and relating this to standardized Chl a and phaeopigment content of the diet, relative to diet weight, it was determined that individual fed 7-day old larvae had a maximum gut content of 1.05±0.09 g diet while 14-day old fed fish had a maximum gut content of 3.17±0.90 g diet. On average, the gut content of 14-day old fish was 2.89 times greater than the gut content of 7-day old fish. The dry weight of larval sea bream increased from 43±4.2 g at day 7 to 134.3±20.4 g at day 14 indicating that growth of fish fed this inert feed was substantial. Gut pigment dynamics suggested that Chl a was degraded to phaeopigments by 7-day but not 14-day old larvae and the individual gut dietary content varied considerably in 14-day old fish. The maximum Chl a and phaeopigment content in larval sea bream was 0.4 ng ind–1 and 0.55 ng ind–1 for 7-day old fish and 1.54 ng ind–1 and 2.81 ng ind–1 for 14-day old fish respectively. The present method may potentially allow simple and direct assessment of larval fish feed ingestion in both an experimental and commercial setting.  相似文献   

20.
Ovarian follicles taken from sexually maturing rainbow trout at the mid-vitellogenic stage of ovarian development were incubated in vitro in the presence or absence of melatonin or somatostatin-14 (SRIF-14) to determine whether there is evidence of a direct action of these factors on gonadal steroidogenesis in fishes. The steroidogenic capacity of the ovarian follicles was assessed by measuring testosterone (T) and 17-estradiol (E2) release into the incubation medium, and by examining the steroid metabolites produced following incubation of follicles with radiolabelled steroid precursors.Melatonin appears to elicit a biphasic effect on steroidogenesis by in vitro rainbow trout ovarian follicles; at a concentration of 1 × 10–3 M, melatonin stimulated basal T and E2 production, but at a concentration of 1 × 10–2 M there was an inhibition of basal and sGtH-stimulated T and E2 Melatonin may act to reduce the activity of specific steroidogenic enzymes, since there was evidence of melatonin at 1 × 10–2 M enhancing the accumulation of [3H]17-hydroxyprogesterone in the medium following incubation with [3H]pregnenolone, possibly suggesting the inhibition of C17,20-lyase activity. In contrast, SRIF-14, used at concentrations of 1 × 10–8 M and 1 × 10–6 M, had no effect on basal or sGtH-stimulated E2 or T production by ovarian follicles, incubated in vitro.  相似文献   

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