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  • 1
    Electronic Resource
    Electronic Resource
    Ultraviolet irradiation of tilapia spermatozoa and the Hertwig effect: electron microscopic analysis (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 42 (1993), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Electron microscopic analysis of U V-irradiated tilapia sperm showed that with irradiation dose of 1800 J m−2 min−1, an irradiation duration of 0.5 min caused decondensation of sperm chromatin. This phenomenon of chromatin decondensation reached a peak after l.5min of irradiation, where ∼ 15% of the sperm showed total decondensation, and was less apparent after 3 min of irradiation or more. Damage to the cytoplasmic membrane and nuclear envelope could be seen in cells that underwent total decondensation. As the duration of irradiation increased, cytoplasmic membrane and nuclear envelope defects appeared more severe, the mitochondria were affected and appeared as empty capsules, and sperm cells tended to lose their tails. Based on these results and others reported in the literature, we propose an explanation for the ‘Hertwig curve’ obtained in tilapia using UV irradiation. Sperm cells with decondensed chromatin and damaged cytoplasmic membrane and nuclear envelope, activate the ‘developmental switch’ when they penetrate the egg, but their pronuclei are subjected to cytoplasmic nuclease digestion. Consequently, the maternal pronucleus is the only functional pronucleus in the zygote, and therefore, only haploid embryos with the exclusive maternal genome are formed. If the paternal pronucleus is not digested, these embryos will die due to improper expression of the paternal genes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.1993.tb00301.x
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  • 2
    Electronic Resource
    Electronic Resource
    Transfer of antibody activity from immunized mother to embryo in tilapias (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 37 (1990), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Antibody activity specific to antigens (PSA, DSA and BGG) which served for immunization of mothers could be measured in extracts of 0-9-day-old embryos spawned by these mothers, using a modified ELISA. The level of antibody activity in embryos varied according to the interval of time between mother immunization and spawning. This activity peaked between 14 and 37 days post-immunization, then it underwent a significant gradual decrease. The activity of the extract was found to be specific only to the antigen which served for the mother immunization and could be adsorbed only by these antigens. The need of mother immunization against selected pathogens for the prevention of larvae and fry mortality is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.1990.tb05856.x
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  • 3
    Electronic Resource
    Electronic Resource
    Comparative study on the induction of triploidy in tilapias, using cold- and heat-shock techniques (1988)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 32 (1988), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Optimal conditions for the induction of triploidy in two different species of tilapia, Oreochromis aureus and Oreachromis niloticus, were determined using either heat-shock or cold-shock techniques. These treatments were applied at conditions that were separately determined for each species. Embryos of these two species were found to differ in their response to heat-shock, but not to cold-shock treatments. The yield of triploid O. niloticus embryos induced at 40.5°C at the zygotic age of 3-5 min did not exceed 13%, in contrast to 60% obtained in O. aureus (heat-shocked at 39.5°C at zygotic age of 3 min). The possibility that the different responses of the two species to heat shock is maternally inherited was supported by the fact that the two-way F1 hybrids also responded in a similar maternally dominant manner. Although the induction of triploidy using heat shock was possible only within a narrow range of zygotic ages (2.5–3.5 and 3.5–4.5 min for O. aureus and O. niloticus, respectively), the induction of triploidy using cold-shock treatment (11°C for 60 min) could be achieved within a wider range of zygotic ages (0–15 min). A satisfactory yield of troploids in the two species (50 and 60% in O. niloticus and O. aureus, respectively) was obtained using this technique. The possible interpretation of these results, that triploidy could be induced by interfering at two distinct meiotic cell-division stages, is discussed. It is concluded that the cold-shock technique is more advantageous for inducing triploidy in O. niloticus, whereas both cold-shock and heat-shock techniques are equally efficient in O. aureus.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.1988.tb05406.x
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  • 4
    Electronic Resource
    Electronic Resource
    Some morphological aspects of fertilization in tilapias (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 36 (1990), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The relationship between the specific anatomy of tilapia gametes and their function was studied in the sequence of events which follow artifical fertilization. Scanning electron microscopic observations showed that some events of the fertilization process, involving spermatozoon migration through the micropylar canal until reaching the villous plasma membrane of the eggs and its penetration into the egg cytoplasm, occur very rapidly (fractions of a second). However, the spermatozoon tail remains outside for about 1–2 min. Then, following the zygote formation and the elevation of the chorion after its separation from the plasma membrane, numerous sperm cells could be found in the vicinity of the micropyle. This cell mass, which seemed to be trapped by a network of microfilaments, was suggested to be the result of the evacuation of excess sperm cells throughout the micropylar canal. The significance of these results for sperm and egg plasma membrane interaction and for prevention of polyspermy are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.1990.tb05617.x
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  • 5
    Electronic Resource
    Electronic Resource
    Further study of the embryonic development of Oreochromis niloticus (Cichlidae, Teleostei) using scanning electron microscopy (1989)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 34 (1989), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The chronology of development of Oreochromis niloticus embryos was examined by scanning electron microscopy (S.E.M.) and the external structures which evolved during the embryonic period were analysed. Twenty-four stages of embryonic development of this fish at 25°C are described with emphasis on the cleavage phases and morphogenesis of external organs and tissues. Because the development of internal organs could not be observed under S.E.M., the necessary investigation was completed by light microscopy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.1989.tb03347.x
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  • 6
    Electronic Resource
    Electronic Resource
    Induction of immunosuppression to bacterial antigens in carp, Cyprinus carpio (1987)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 31 (1987), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Typical primary antibody responses were found after injecting carp maintained at 25°C with formalin-killed (Fk) Vibrio anguillarum bacteria, but not in fish injected with the same antigen held at 12° C. There were no significant increases over the primary responses in fish receiving a second injection 60 days after the first injection.The differences in the results between fish groups receiving three V. anguillarum antigens at two dosages were found to be insignificant in most of the experiments. A comparison of the antibody titres of fish groups after challenge with Fk bacteria showed no difference from control fish receiving a single injection similar to the challenge dose or fish receiving a previous injection with the antigens emulsified in complete Freund's adjuvant (CFA) at 25° C. However, significant immunosuppression was found in fish that were given the primary injection intracardially at 25° C or 12° C, or with CFA emulsion at 12° C.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.1987.tb05300.x
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  • 7
    Electronic Resource
    Electronic Resource
    The effect of fish age on the mortality caused by selected fish pathogens (1987)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 31 (1987), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.1987.tb05324.x
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  • 8
    Electronic Resource
    Electronic Resource
    Sex-determining genes in tilapia: a model of genetic recombination emerging from sex ratio results of three generations of diploid gynogenetic Oreochromis aureus (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 37 (1990), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Three major findings emerged from this study: (1) the existence of gynogenetic males among first, second and third generations of gynogenetic tilapias; (2) the sex ratios amongst gynogenetic offspring reflect two genetically different maternal types, the first type giving rise to both gynogenetic males and females, and the second type only to females; (3) females of the first maternal type produce more gynogenetic female than male offspring. On the basis of a genetic recombination model between sex-determining genes and the centromere, the first maternal type was defined as heterogametic (WY) and the second as homogametic (WW). This model suggests that females with the WY combination can produce in all descending gynogenetic generations offspring expressing the three above gynotypes, and this suggestion is consistent with our FI–F3 sex ratio results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.1990.tb05937.x
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  • 9
    Electronic Resource
    Electronic Resource
    The induction of triploidy in Oreochromis aureus by heat shock (1986)
    Springer
    Theoretical and applied genetics 72 (1986), S. 186-192 
    Details
    ISSN: 1432-2242
    Keywords: Oreochromis ; Tilapia ; Polyploidy ; Triploidy ; Heat-shock
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Triploid fish were obtained using heat-shock treatment. The optimal conditions for the heat shock (39.5±0.2°C for 3.5–4 min) as well as the exact zygote age (3 min) at which this heat shock was applied were studied. Results showed that this treatment gives rise to 100% of triploid fish with a satisfactory survival rate of 61% beyond the yolk sac resorption. The genital papillae of this triploid fish were underdeveloped in comparison to normal diploid fish. However, no morphological or growth-rate differences between diploid and triploid fish could be observed up to the age of 6 months. Triploidy was assessed by the karyotyping of embryo cells or adult PHA-stimulated lymphocytes, or by erythrocyte measurements. The occurrence of a heat-shock sensitive event at the zygotic age of 6 min is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00266991
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  • 10
    Electronic Resource
    Electronic Resource
    Sex determination in Sarotherodon (tilapia) (1979)
    Springer
    Theoretical and applied genetics 55 (1979), S. 177-187 
    Details
    ISSN: 1432-2242
    Keywords: Sarotherodon (Tilapia) ; Sex determination ; Theoretical model ; Autosomal influence ; Sex chromosomes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The simplest possible model of the sex determination process adding autosomal influence to a minimal number of sex chromosomes was developed to explain matings of Tilapia (Sarotherodon) species. Eighteen different genotypes, each having two autosomes (AA, Aa, or aa) and two sex chromosomes (WX, WY, WW, XY, XX or YY) involved in sex determination, are predicted by the theory. Their sex (10 males and 8 females) were determined using a series of directed graphs, showing the relative strength of the chromosome pairs, developed on the basis of Chen's sex ratio results (Chen 1969). This theoretical model predicts eight different sex ratios (0∶1, 1∶3, 3∶5, 1∶1, 9∶7, 5∶3, 3∶1, 1∶0 ♀∶♂); three of them are not predicted by the WXYZ theory. The greatest part of these sex ratios have been obtained experimentally in extensive series of crosses between related species of Tilapia and their hybrids, carried out by several authors. The theory succeeds in explaining all of Chen's results, including those ratios 5∶3 and 0∶1 seen in certain crosses but not predicted by the WXYZ theory. The importance of the autosomes is seen in comparisons of the genotype pairs (AaWY, aaWY), (AaXY, aaXY) and (AAWW, AaWW) in which the first genotype in each case is male while the second is female as proven by the sex ratio results. The members of the pair differ only in the substitution of one autosome for the other. To test the theory, experiments consisting of hormonal sex reversion and a series of crosses are proposed. Finally, theoretical and practical implications of the theory are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00295445
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