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  • 1
    Electronic Resource
    Electronic Resource
    Hormonal sex reversal of tilapias: implications of hormone treatment application in closed water systems (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Aquaculture research 28 (1997), S. 0 
    Details
    ISSN: 1365-2109
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The phenomenon of incidental sex reversal was observed in experiments originally designed to determine the importance of feeding duration and feed quality in the optimization of masculinization and feminization treatments of Oreochromis niloticus (L.) fry by oral application of hormones. Four separate experiments were conducted: (1) masculinization and (2) feminization using three feeding durations and (3) masculinization and (4) feminization using three alternative feed mixtures. Masculinization experiments incorporating 17 α-methyltestosterone (MT) into the feed at 40 mg kg−1 were applied to putative monosex male progeny whilst feminization treatments were applied to putative all female fry using diethylstilboestrol (DES) at 1000 mg kg−1. Treatments were applied outdoors in small cages suspended in 900-l circular concrete tanks with a flow through rate of 1-l min−1. Replicate cages for all treatments and the controls in each experiment were reared together in the same tank. Only the first experiment produced significant differences in sex ratio, with the control treatment producing a slightly lower proportion of males than the three MT treatments at different durations. The most significant finding was that in all experiments the sex ratio of the control differed significantly from expectations and in all but experiment 1, did not differ from those of the treated fish in which sex reversal had clearly been effected. It appears likely that incidental sex reversal occurred in the control fish as a result of the accumulation of active metabolites from the treated fish and/or leachates from uneaten food given to fish in the same water body. The results are discussed in the context of improving the efficiency and safety of hormonal sex reversal treatments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2109.1997.00878.x
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  • 2
    Electronic Resource
    Electronic Resource
    Small-scale fry production systems for Nile tilapia, Oreochromis niloticus (L.) (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Aquaculture research 24 (1993), S. 0 
    Details
    ISSN: 1365-2109
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Experiments were conducted to evaluate and compare the production, quality and survival of eggs and the subsequent growth and survival of fry in two small-scale production systems: natural incubation and egg collection followed by artificial incubation. Artificial incubation produced a significantly greater number and biomass of fry per unit weight of female broodstock (P 〈 0·05). This was due to the significantly decreased spawning interval in females from which eggs were collected (mean = 23· days) compared to naturally incubating females (mean = 36·8 days). It is also hypothesized that survival during artificial incubation (85%) is greater than in natural incubation. Cost-benefit analysis demonstrated a threefold increase in total net returns for artificial incubation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2109.1993.tb00545.x
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  • 3
    Electronic Resource
    Electronic Resource
    ‘Blond’: a useful new genetic marker in the tilapia, Oreochromis niloticus (L.) (1987)
    Oxford, UK : Blackwell Publishing Ltd
    Aquaculture research 18 (1987), S. 0 
    Details
    ISSN: 1365-2109
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract. Breeding tests demonstrate that a blond mutant showing a marked reduction of melanin in chromatophores, arising within a laboratory population of Oreochromis niloticus (L.) is due to a single autosomal recessive gene. Possible commercial and research benefits of this character are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2109.1987.tb00134.x
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  • 4
    Electronic Resource
    Electronic Resource
    The effect of luteinizing hormone-releasing hormone analogue (LHRHa) on sperm count of Oreochromis niloticus (L.) (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Aquaculture research 27 (1996), S. 0 
    Details
    ISSN: 1365-2109
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: An experiment was conducted to compare the potency of different levels of luteinizing hormone-releasing hormone analogue (LHRHa) for increasing the sperm counts in sexually mature male Oreochromis niloticus (L.). One hundred males (106.49 ± 3.59g, 15.2 7 ± 0.20 cm) were randomly distributed in four treatment groups, each receiving intramuscular injections of: (i) control, 0.05 ml phosphate-buffered saline, (ii) 10 μg kg-1 LHRHa, (iii) 20 μ kg-1 LHRHa and (iv) 30 μ kg-1 LHRHa. Sperm counts were determined prior to injection (day 0) and for four consecutive days (days 1 to 4) thereafter. Results showed a significant increase in sperm counts (P 〈 0.01) 1 day after injection among males injected with 10 to 20 μ kg-1 LHRHa. The effect of injecting 30 μ kg-1 LHRHa is similar to that in the control group. Across all treatments, sperm counts declined with time over the 4-day sampling period.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2109.1996.tb00972.x
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  • 5
    Electronic Resource
    Electronic Resource
    Biodiversity in aquatic systems in relation to aquaculture (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Aquaculture research 28 (1997), S. 0 
    Details
    ISSN: 1365-2109
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: This paper first considers the perception and dimensions of biodiversity. We suggest that biodiversity can be viewed as a biospatial, hierarchically distributed structure of variability among living organisms with five levels of complexity (and including agricultural systems). Loss of biodiversity, value of biodiversity and knowledge of aquatic biodiversity are reviewed briefly. Methods for measuring biodiversity, especially at the genetic level, are discussed and considerable emphasis is laid on effective population size as a controlling factor in biodiversity.Finally, a range of impacts of aquaculture upon biodiversity are considered, including competitive and introgressive effects from farmed stocks. The development and use of reversibly sterile strains is seen as highly beneficial to both aquaculture and the maintenance of biodiversity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2109.1997.00947.x
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  • 6
    Electronic Resource
    Electronic Resource
    A technique for sampling muscle tissue from live fish (1989)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 35 (1989), 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.1095-8649.1989.tb03404.x
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  • 7
    Electronic Resource
    Electronic Resource
    Caudal deformity syndrome (CDS): an autosomal recessive lethal mutation in the tilapia, Oreochromis niloticus (L.) (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish diseases 15 (1992), S. 0 
    Details
    ISSN: 1365-2761
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Abstract. Deformities consisting of an upward curvature of the spine in the caudal region with varying degrees of reduction of the caudal fin were observed in some fry of a laboratory population of Oreochromis niloticus (L.). This spinal deformity was combined with a reduction of the operculum, exposing some gill lamellae. No deformed fry survived for more than 7 days after completion of yolk sac absorption. Breeding tests demonstrate that the mutant phenotype is controlled by a single autosomal recessive gene.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2761.1992.tb00638.x
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  • 8
    Electronic Resource
    Electronic Resource
    Sex determination in the genus Oreochromis (1991)
    Springer
    Theoretical and applied genetics 82 (1991), S. 144-152 
    Details
    ISSN: 1432-2242
    Keywords: Sex determination ; Oreochromis niloticus ; Gynogenesis ; Sex reversal ; Triploidy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Established techniques of genetic manipulation were used to elucidate sex-determining mechanisms in the commercially important tilapia, Oreochromis niloticus. Analysis of sex ratios from single-pair matings of normal broodstock showed these to be heterogeneous, with an asymmetrical frequency distribution. Data were homogeneous, with the exclusion of a number of broods with sex ratios not significantly different from 3∶1 (male: female), and further progeny testing revealed atypical female heterogamety in the parents of these broods. Analysis of sex ratios from complete diallele-type crosses using five males and five females demonstrated no association between male parent, female parent and progeny sex ratio. Sex ratios of gynogens (0∶1) and triploids (1∶1), and from progeny testing of sex-reversed males (0∶1) and sex-reversed females (3∶1), provide evidence for female homogamety in this species. Progeny testing of male gynogens derived from sex-reversed females demonstrated recombination between the centromere and the sex-determining locus (68.9%). Novel YY “supermales” were shown to be viable and produced all-male offspring. It was concluded that this species exhibits monofactorial, genotypic sex determination with male heterogamety. However, rare autosomal or environmental sex-modifying factors may account for occasional deviations from expected sex ratios.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00226205
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  • 9
    Electronic Resource
    Electronic Resource
    Sex determination in the genus Oreochromis (1991)
    Springer
    Theoretical and applied genetics 82 (1991), S. 153-160 
    Details
    ISSN: 1432-2242
    Keywords: Sex determination ; Oreochromis aureus ; Gynogenesis ; Sex reversal ; Hybridisation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Sex ratios from 62 single-pair matings of normal broodstock O. aureus were highly heterogeneous with an overall deficit of males (41.4%). Peaks in the sex ratio frequency distribution occurred at 1∶1, 3∶5 and 1∶3 (male∶female). Hybridisation of O. aureus with O. mossambicus, O. spilums and O. niloticus produced highly variable sex ratios, suggesting a complexity of hybrid sex determination. Few valid inferences could be made regarding intraspecific sex determination from these hybrid data. Sex ratios from progeny testing of sex-reversed males (1∶3) and most sex-reversed females (1∶0) provide evidence for female heterogamety in O. aureus. Several aberrant ratios observed suggest Mendelian inheritance of an autosomal recessive gene (F,f), epistatic to the major sex-determining gene (W,Z). Sex ratios of triploids and gynogens support the hypothesis of recombination between the centromere and the major sex-determining locus. Progeny testing of a female mitogyne demonstrated the viability of a novel WW “superfemale”, which gave only female offspring. Not all data could be explained by a two-factor model of sex determination. Further exceptional sex ratios may be accounted for by rare autosomal or environmental sex-modifying factors. It is concluded that O. aureus has a multifactorial mechanism of sex determination with the underlying primary mechanism of female heterogamety.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00226206
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