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  • 2000-2004  (9)
  • 1
    Electronic Resource
    Electronic Resource
    Relative potency of the forms of GnRH and their analogs on LH release in sea bass (2003)
    Oxford, UK : Blackwell Science Ltd
    Journal of fish biology 63 (2003), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The in vivo and in vitro potency of native and modified forms of gonadotropin releasing hormone (GnRH) to release luteotropic hormone (LH) was studied in sea bass Dicentrarchus labrax in particular the hypothalamic fish-specific sea bream GnRH form (sbGnRH) and the general mesoencephalic form chicken GnRH-II (cGnRH-II). The potencies of the natives and their analogs (GnRHas) were referred to that of [D-Ala6, Pro9Net]-mGnRHa (LHRHa) at equivalent doses. Analogs of the native peptides [D-Arg6, Pro9Net]-cGnRH-II, [D-Ala6, Pro9Net]-cGnRH-II, [D-Trp6, Pro9Net]-sbGnRH and [D-Ala6, Pro9Net]-sbGnRH were effective in inducing in vivo LH release (at 15 µg kg−1 body mass), exhibiting longer lasting activity than their corresponding native forms. Injection of sbGnRH and cGnRH-II provoked a small but significant peak of circulating LH at 1·5 h after treatment (a.t.) decreasing down to basal levels at 4 h a.t. [D-Arg6, Pro9Net]-cGnRH-II, [D-Ala6, Pro9Net]-cGnRH-II and [D-Ala6, Pro9Net]-mGnRHa evoked a higher and a more sustained elevation of LH, peaking at 12 h a.t. and returning to basal levels between 48 and 72 h a.t. [D-Trp6, Pro9Net]-sbGnRH and [D-Ala6, Pro9Net]-sbGnRH also induced a significant surge of LH in plasma at 4 h a.t. turning to the basal levels at 24 h a.t. These rises, however, were of less amplitude and duration than the observed after treatment with cGnRH-II analogs and [D-Ala6, Pro9Net]-mGnRHa. The in vitro stimulation of dispersed pituitary cells with the different native and modified forms of GnRH resulted in a dose-dependent increase in the quantity of LH released at 24 h a.t. [D-Arg6, Pro9Net]-cGnRH-II and [D-Ala6, Pro9Net]-cGnRH-II induced the highest response of LH in vitro release followed by salmon GnRH (sGnRH), [D-Ala6, Pro9Net]-mGnRHa and [D-Trp6, Pro9Net]-sbGnRH. The lowest activity was exhibited by sbGnRH. Collectively, the in vitro biological activity (compared by their EC50) can be ordered as follows: [D-Arg6, Pro9Net]-cGnRH-II 〉 [D-Ala6, Pro9Net]-cGnRH-II 〉 sGnRH 〉 [D-Ala6, Pro9Net]-mGnRHa 〉 [D-Trp6, Pro9Net]-sbGnRH 〉 [D-Ala6, Pro9Net]-sbGnRH 〉 cGnRH-II 〉 sbGnRH.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1095-8649.2003.00130.x
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  • 2
    Electronic Resource
    Electronic Resource
    Comparative growth performance of diploid and triploid European sea bass over the first four spawning seasons (2001)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 58 (2001), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: During their 3–4 first years of life, triploid sea bass Dicentrarchus labrax grew in a similar fashion to diploids in fork length but more slowly than diploids (P〈0·05) in body weight, even when the diploids reached full sexual maturity. However, from 48–53 months of age triploids exhibited non-significantly higher instantaneous growth rates, and thus when fish were 4 years or older, differences in weight with diploids were no longer apparent, suggesting that triploidy could be of benefit in the culture of large (〉1 kg) sea bass. The condition factor was reduced in both ploidies during the spawning season which took place in winter when the temperature was low. These observations suggest that any growth advantage in triploids, which were functionally sterile, may be offset by unfavourable environmental conditions. Thus, the potential gain of triploid fish, because they do not direct energy to gonadal growth, could not overcome the effects of low temperature on somatic growth, which coincided with the spawning season. This suggests that the low growth of this species during winter is more a consequence of low temperature than of the energetic cost associated with reproduction. On the other hand, the lower hepatosomatic index in triploid females in contrast to diploid females might be indicative of the lack of gonadal oestradiol-mediated hepatic synthesis of vitellogenin. Also, erythrocyte and haematocrit measurements showed an increased nuclear and cellular volume in triploids, but with similar cell numbers to those of diploids, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.2001.tb00500.x
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  • 3
    Electronic Resource
    Electronic Resource
    Hormonal regulation of the European sea bass reproductive cycle: an individualized female approach (2000)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 56 (2000), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Fifteen tagged female sea bass Dicentrarchus labrax were sampled weekly from September to April and plasma vitellogenin (VTG), testosterone (T), 17β-estradiol (E2), and two potential maturation inducing steroids (MISs): 17,20β-dihydroxy-4-pregnen-3-one (17,20βP) and 17,20β,21-trihydroxy-4-pregnen-3-one (20βS) assayed. An oocyte sample was obtained via intraovarian cannulation at each sampling time from every female and the stage of development of the most advanced clutch of oocytes determined and related to VTG and hormone plasma levels for each female. The mean number of ovulations per female was 1·75+0·25 when those females that did not present ovulations were excluded and up to 4 ovulations detected in some females. The highest plasma levels of T (c. 6 ng ml-1) were observed during postvitellogenesis and the beginning of maturation while maximum plasma levels of E2 (〉5 ng ml-1) were obtained during late vitellogenesis. VTG plasma levels increased throughout vitellogenesis peaking (c. 2·5 mg ml-1) at postvittelogenesis. For the first time significant changes of plasma progestogens were detected in European sea bass during the sexual cycle. The highest plasma level of 17,20βP (c. 1·1 ng ml-1) was observed during postvitellogenesis while the highest level of 20βS (c. 1·4 ng ml-1) coincided with final maturation. These results suggest that 17,20βP and 20βS play a role in the early and final maturation, respectively, in the European sea bass.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.2000.tb02131.x
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  • 4
    Electronic Resource
    Electronic Resource
    Luteinizing hormone and sexual steroid plasma levels after treatment of European sea bass with sustained-release delivery systems for gonadotropin-releasing hormone analogue (2002)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 60 (2002), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Spermiating male European sea bass Dicentrarchus labrax were treated with gonadotropin-releasing hormone agonists (GnRHa), either a GnRHa injection (IN; 25 μg kg−1 body mass) or one of three types of controlled-release GnRHa-delivery systems: fast release implants (EVAc; 1OO μg kg−1), slow release implants (EVSL; lOO μg kg−1) and slow release microspheres (MC; 50 μg kg−1). Luteinizing hormone (LH) release was highly stimulated by all GnRHa treatments, with elevated plasma levels lasting for 2 days in injected fish (IN) and 2, 4 and 6 weeks in controlled-release-treated fish (EVAc, MC and EVSL, respectively), correlating with a 1, 3, 5 and 5 week period of stimulation of milt production, respectively. Plasma levels of the androgens testosterone (T) and 11-ketotestosterone (11-KT), were not significantly affected by the GnRHa treatments. Plasma T was high at early spermiation and declined sharply near the end of this period. Plasma 11-KT levels declined continuously throughout the experiment. Levels of 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P), a proposed maturation-inducing steroid (MIS) in European sea bass, fluctuated around 0.2–1 ng ml−1 and were not greatly affected by the treatments. These results indicated a close correlation between sustained stimulation of LH release, achieved by GnRHa-delivery systems, and long-term enhancement of milt production. They also show an absence of changes in the common sex steroids, associated with elevated LH and enhanced spermiation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.2002.tb00283.x
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  • 5
    Electronic Resource
    Electronic Resource
    Growth, gonadal development and sex ratios of meiogynogenetic diploid sea bass (2002)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 61 (2002), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Gynogenesis showed little effect on general physiology and gonadal development in sea bass Dicentrarchus labrax. Meiogynogenetic fish showed well-developed gonads indicating low occurrence of developmental imbalances even after gynogenesis induction in this species. In addition, the proportion of sexes of meiogynogenetic sea bass was similar to the diploid controls in two independent trials, which did not deviate significantly from a 1:1 male: female sex ratio. Even considering some environmental influence on sex differentiation, as has been previously demonstrated, the fact that the proportion of sexes was similar between gynogenetic and control diploids essentially eliminates the possibility that in the sea bass the females are the homogametic sex. Although the mechanism of sex determination of this species still remains unknown, even after gynogenesis induction, the genetic mechanism of the ZW/ZZ type could probably operate in the sea bass.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.2002.tb01570.x
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  • 6
    Electronic Resource
    Electronic Resource
    Effects of polyunsaturated fatty acids and gonadotropin on prostaglandin series E production in a primary testis cell culture system for the European sea bass (2000)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 57 (2000), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Prostaglandin series E (PGE) production by mixed populations of isolated sea bass Dicentrarchus labrax testicular cells was measured after culture at 20° C in L-15 for up to 24 h in the absence or presence of arachidonic acid (AA), eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) and/or gonadotropin (hCG). AA stimulated a significant dose- and time-dependent increase in PGE production. EPA stimulated PGE production only during the first 6 h although levels were 26·4% those induced with AA; DHA reduced PGE production. Although hCG alone had no effect, it enhanced AA-induced PGE formation and suppressed EPA-induced PGE production. These results suggest that essential PUFAs modulate significantly testicular PGE production in vitro and therefore may have important effects on steroidogenesis and spermiation in the male European sea bass.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.2000.tb02232.x
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  • 7
    Electronic Resource
    Electronic Resource
    Critical period of androgen-inducible sex differentiation in a teleost fish, the European sea bass (2001)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 58 (2001), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Twenty-day exposures to 17α-methyltestosterone (MT) (10 mg kg-©1 food) starting at 86 or 106 days post fertilization (DPF) resulted in a complete masculinization of sea bass Dicentrarchus labrax, as opposed to 46% females present in the controls. Earlier exposures failed to suppress ovarian development, resulting in a variable number of females (range 10·5–49·5%). All treatments assayed between 110 and 210 DPF induced a complete masculinization, regardless of the androgen or the dose tested. However, a dose dependent increase in the number of fish with intratesticular oocytes was observed after MT but not after 17α-methyldihydrotestosterone (MDHT) administration. This might be a reflection of the capability of MT and not of MDHT to be converted into oestradiol by the action of aromatase. One hundred-day exposures to either of the androgens (10 mg kg©1 food) starting at 60 or 160 DPF resulted in a total suppression of ovarian development and a partial induction of sterility. Complete sterility was accomplished after 200 days of exposure starting at early ontogenesis (60–260 DPF). These deleterious effects on gonadal development were later confirmed by a dramatic reduction of the gonadosomatic index. In addition, around the first year of age, growth was significantly depressed in all groups except those for which treatments started at the latest (160–260 DPF; experiment 1) or the earliest and shortest (46–66 DPF; experiment 2). Hence, the critical period of androgen-inducible masculinization is located between 96 and 126 DPF and coincides with a rapid proliferation of primordial germ cells in the sexually undifferentiated gonad.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.2001.tb02257.x
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  • 8
    Electronic Resource
    Electronic Resource
    Development and validation of an enzyme immunoassay for testosterone: Effects of photoperiod on plasma testosterone levels and gonadal development in male sea bass (Dicentrarchus labrax, L.) at puberty (2000)
    Springer
    Fish physiology and biochemistry 23 (2000), S. 141-150 
    Details
    ISSN: 1573-5168
    Keywords: accelerating photoperiods ; EIA validation ; first sexual maturation ; sea bass ; testosterone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A specific immunoassay was developed for the quantification of testosterone (T) in sea bass plasma. Specific primary antibody against T was produced using an antigen BSA conjugated with T. The enzyme immunoassay (EIA) had a sensitivity of 5–0.009 ng ml−1 and 6.2% intra-assay variation; inter-assay variation was 9.5% for sea bass plasma. The effects of two different accelerating photoperiod regimes, compressed photoperiod (CO; 6 months), and constant short photoperiod (9L:15D) with a long photoperiod (15L:9D) in March (SLmar), on T plasma levels and sexual maturation were examined during the onset of puberty in male sea bass. Natural photoperiod (NP) and SLmar groups exhibited the highest T values in December (8.69±1.03 and 10.85±1.04 ng ml−1, respectively). However, SLmar group showed the first significant decrease in T plasma levels in January, two months earlier than the NP group, which presented elevated T levels until February. The CO group displayed two significant T peaks, one in October (8.90±1.60 ng ml−1) and the other in January (9.60±1.10 ng ml−1). Gonadosomatic index (GSI) in the NP and SLmar groups displayed the highest values from December to February (〉2.5%). However, the SLmar group showed the first significant increase in GSI in November, one month before the controls, indicating a clear advancement of gonadal development with respect to the NP group. In the CO group, a bimodal pattern was observed with two peaks, one in October–November (1.30±0.25%) and the second in March–April (0.97±0.33%) (P〈0.05). In NP group, the percentage of running males was about 80% from December to March while the percentage of running males in the SLmar group (∼70%) lasted only three months (December to February) decreasing (P〈0.05) in March. In the CO group, spermiation began in October (60%), decreased during the next months, and increased again in March–April (30%) (P〈0.05). These results indicate the advancement of puberty by either one or two months with respect to the control group in the SLmar and CO groups, respectively, and the presence of a second reproductive surge in the CO group. Collectively, these results suggest that exposure of fish to these photoperiod regimes may affect both the time of the onset of puberty and the pattern of gonadal development in prepuberal male sea bass.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007871604795
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  • 9
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    A one-step approach to obtain cell clones expressing tetracycline-responsive transactivators (2004)
    Elsevier
    Details
    Publication Date: 2004-08-01
    Print ISSN: 0003-2697
    Electronic ISSN: 1096-0309
    Topics: Biology , Chemistry and Pharmacology
    Published by Elsevier
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