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Title: Applications of gynogenesis and sex reversal to improvement of tilapia
Author: Gilling, C. J.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1995
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Techniques applicable to the improvement of the commercially important warm water fishes, of the genus Oreochromis, by means of monosex production were investigated. The results of three approaches are described. First, hydrostatic pressure shocks were used to interrupt the second meiotic division and restore diploidy to haploid eggs which had been activated by UV denatured sperm. A hydrostatic pressure shock of 8,500 p.s.i. applied 8.5 minutes after fertilisation for a duration of 3 minutes was found to be the optimum for restoration of diploidy. The survival of diploid gynogens produced by this method compared favourably to those produced by heat shock, the most commonly applied technique. Second, feminisation of sexually undifferentiated fry was achieved through a hormone immersion method. At the same concentrations the synthetic oestrogens, ethynyestradiol and diethylstilbestrol were more effective than the naturally occurring oestrogen, 17β-estradiol, in inducing feminisation when they were dissolved in the water in which the fry were reared. Reliable feminisation (92 - 100% females) was achieved by immersing fry for 18 days in Ethynylestradiol at a concentration of 180 μg l-1, starting treatment at the time of first feeding. Attempts to induce feminisation by short immersions in oestrogen solutions at high concentrations were less reliable. Sex reversed females were identified and used to produce "YY" males. Third, all-male interspecific hybrids were produced by crossing Oreochromis jipe males with O.niloticus and O.aureus females. Growth trials comparing O.jipe X O.aureus hybrids with intraspecific crosses provided evidence of heterosis for early growth rate in interspecific hybrids. The genetic basis of sex determination in some commercially cultured Oreochromis hybrid strains is discussed and evidence suggesting that this is more complex than in laboratory reference Oreochromis populations is presented. However, sex reversal and selection of one commercially used strain of hybrid origin yielded all-male producing "YY" males, but no "YY" females.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available