This thesis presents investigations into different possible approaches for genetic control of sex ratio in Nile tilapia <I>Oreochromis</I> <I>niloticus</I> through the use of YY-male technology. The production of YY-males in the Egypt-AIT strain using a model described by Mair <I>et al</I>. (1993) has been achieved in this study. Male percentages in progeny sired by YY-males were highly variable, ranging from 36% to 100% with a mean of 80.6%. Sex ratios in progenies from repeated spawns of the same pairs were significantly heterogeneous (P<0.001). To determine the underlying variability in sex ratio, 95 progeny groups from intraspecific crosses of normal broodstock of the Egypt-AIT strain were sexed. In addition, diallele-type crosses were generated from seven females and five males. Male percentages in individual progenies ranged widely from 15.5% to 100%. Over 53% of crosses produced a sex ratio significantly different from 1:1 (P<0.05). Analysis of sex ratios from the diallele-type crosses demonstrated both maternal and paternal effects on progeny sex ratio. Interstrain hybrid YY-males were produced by crossbreeding and backcrossing. Male percentages in progeny from crosses of hybrid YY-males and Egypt-AIT females were very variable, ranging from 61% to 100% with a mean of 84.1%. Sex ratios in progeny from repeated spawns of the same pairs were very inconsistent. Production of interstrain GMT (genetically male tilapia) by crossing YY-males of the Egypt-Swansea with Egypt-AIT females was investigated. Male percentages in interstrain GMT ranged from 53.5% to 100% with a mean of 93.1%. An attempt was made to produce a consistently high proportion of males in interstrain GMT through selection of a female line in the Egypt-AIT strain. However, the preliminary results indicated no response to selection. The research in this thesis demonstrates that in addition to the indirect introduction of Egypt-Swansea YY-males, YY-males of the Egypt-AIR strain and interstrain YY-males could both be used as genetic approaches for sex control in <I>O. niloticus</I>. The Egypt-AIT GMT and interstrain GMT are likely to become the preferred GMT for cage culture at least in Thailand.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:638518 |
| Date | January 1997 |
| Creators | Pham, A. T. P. |
| Publisher | Swansea University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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