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  • 1
    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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  • 2
    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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  • 3
    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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  • 4
    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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  • 5
    Electronic Resource
    Electronic Resource
    The impact of seasonal alteration in the lipid composition of broodstock diets on egg quality in the European sea bass (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 51 (1997), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Groups of European sea bass Dicentrarchus labrax L., broodstock were fed two pelleted, lipid-enriched diets [maize oil, low essential fatty acid (EFA) or fish oil, high EFA]. Those fed the high EFA diet for 12 months or only during vitellogenesis (September to February) with the low EFA diet fed for the remaining 6 months, showed improved egg quality and higher hatching rates when compared to two groups fed the high EFA diet during either previtel-logenesis (February to September) or the spawning period (February to April). The higher quality eggs contained higher levels of total n-3 fatty acids, including increased levels of both docosahexaenoic acid (DHA) and eicosapaentaenoic acid (EPA). High levels of triacylglycerol (TAG) were linked with the poorer quality eggs from those groups fed the low EFA diet during the period of vitellogenesis. The present work identifies vitellogenesis as the period in the maturation during which EFA are incorporated most effectively into the developing oocytes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.1997.tb01997.x
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  • 6
    Electronic Resource
    Electronic Resource
    In vitro oocyte maturation in the sea bass: effects of hCG, pituitary extract and steroids (1999)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 55 (1999), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Exposure of sea bass Dicentrarchus labrax oocytes to 25, 50, 100, and 300 IU ml−1 of human chorionic gonadotropin (hCG) resulted in a dose-dependent increase (ED50=60 IU ml−1) in the maximal maturation and volume response rate over a 120-h incubation period. Oocytes responded in a similar dose-dependent manner to graded doses of homologous sea bass pituitary extract (ED50=3·3#10−2 PE ml−1). The response latency of sea bass oocytes to endogenous and exogenous gonadotropins was similar (t1/2≃45 and 48 h, respectively). Both 17α,20β-dihydroxy-4-pregnen-3-one (17,20βP) and 17α,20β,21-trihydroxy-4-pregnen-3-one (20βS) stimulated maturation in a dose- and time-dependent manner with t1/2 values less than those of hCG (15 h and 7·5 h at 100 ng ml−1, respectively); 17α,20α-dehydroxy-4-pregnen-3-one (17,20αP) was ineffective. 17,20βP was more potent at all doses tested. The stimulatory actions of gonadotropin and maturation-inducing steroid (MIS) involved both transcription and translation since maturation was significantly inhibited in the presence of actinomycin D and cycloheximide. Moreover, pituitary extract and hCG stimulated release of higher levels of 17,20βP in a dose- and time-dependent manner in follicle incubations as compared to 20βS suggesting that this steroid may in fact be the MIS in this species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.1999.tb00652.x
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  • 7
    Electronic Resource
    Electronic Resource
    Effects of constant short and long photoperiod regimes on the spawning performance and sex steroid levels of female and male sea bass (1999)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 54 (1999), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Under constant short photoperiod, the spawning time of 2-year-old sea bass Dicentrarchus labrax was advanced as compared to controls, whereas spawnings were delayed under constant long photoperiod. High plasma levels of 17β-oestradiol (E2/) and testosterone (T) in females were coincident with the appearance of vitellogenic oocytes in the ovary, while high levels of 11-ketotestosterone (11-KT) and T in males were coincident with the presence of spermiating males. Although plasma levels of E2 in females and 11-KT in males were low during the remainder of the cycle, levels of T were always 〉1 ng ml−1 in both sexes, suggesting that T could play an important role during the initial stages of gonadal development. The profiles of E2 and T in females and 11-KT and T in males exposed to constant short days were similar to those in the control group, but fish which were maintained under constant long photoperiods showed a bimodal pattern of these steroids. The results obtained from fish exposed to constant photoperiod regimes provide further evidence that an endogenous process could be operating to control the reproduction of sea bass.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.1999.tb00617.x
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  • 8
    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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  • 9
    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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  • 10
    Electronic Resource
    Electronic Resource
    Pattern of sea bass oocyte development after ovarian stimulation by LHRHa (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 41 (1992), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The cyclic pattern of oocyte development in the sea bass, Dicentrarchus labrax L., was studied after induction of spawning by two injections, 24 h apart, of a luteinizing hormone releasing-hormone analog (LHRHa) administered at the end of vitellogenesis. The first difference in the developmental stage of the ovary and in the size-frequency distribution of oocytes between the LHRHa treated group and the control group, was detected 32 h after the first injection, the LHRHa group showing a higher proportion of the 900 μm diameter oocyte class (maturing oocytes) (P〈0.01). At 48 h LHRHa-treated females showed an increase in the 1000 and 1100 μm classes (maturing oocyte and ovulated eggs) (P〈0.01) and at 72 h these females exhibited a bimodal pattern, reaching the highest proportions in the 1100 (27.4%) and the 600 (14.7%) μm classes (ovulated eggs and advanced vitellogenic oocytes, respectively). Bimodal distributions were present in 80% of the LHRHa-treated females. Once oocyte final maturation was triggered by LHRHa the time needed for ovulation was about 48 h and the interval between consecutive ovulations and spawnings seemed to be 48–72 h.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.1992.tb02723.x
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