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  • Blackwell Publishing Ltd  (11)
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  • 1
    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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  • 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
    Sex ratios in offspring of sex-reversed sea bass and the relationship between growth and phenotypic sex differentiation (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: Groups of sexually undifferentiated sea bass Dicentrarchus labrax were fed with the androgen 17α-methyltestosterone (MT) during sex differentiation. MT treatment increased males from 79±3% in the controls (the usual 3:1 male:female sex ratio of cultured sea bass) to 100±0%, implying that in the treated groups one out of each five resulting males was a masculinized female (neomale). Thirteen males from the MT treated groups were taken as the parental generation and their sperm used to individually fertilize a pool of eggs from unrelated females. The probability of having at least one neomale was 95% and most probably two or three of the males used were neomales. The offspring from each family were reared separately under the same environmental conditions. Samples were taken at 11 and 15 months of age, during and after sex differentiation, respectively. Results showed that females predominated among the larger fish whereas males and undifferentiated fish predominated among the smaller ones. Intersexes exhibited an intermediate size. All fish with a body length smaller than 12 cm were undifferentiated. These results suggest that sex differentiation is more dependent on length than on age. At 15 months, sex ratios were male-biased in all families, except one (females ranged from 5 to 50%) and only two families had sex ratios not significantly different from 1:1, suggesting that the mechanism of sex determination in the sea bass is not of a XX/XY or ZW/ZZ type since no family exhibited a female-biased progeny, as would be expected from both types. Results support the hypothesis that factors other than genetic, i.e., environmental, may act epigenetically on the sex determination mechanisms of sea bass, as has been demonstrated in other fishes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.1999.tb00730.x
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  • 7
    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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  • 8
    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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  • 9
    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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  • 10
    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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