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Title: Genetic and environmental factors affecting growth and sex ratio in the nile tilapia, Oreochromis niloticus L.
Author: Abucay, J.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 1998
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A series of experiments evaluating the effect of temperature and salinity on sex ratio in sexually undifferentiated putative all-female, all-male and YY males were conducted. High temperature (36oC) was observed to affect the sex ratio towards male and towards female in different circumstances. Purebred YY males (Egypt-Swansea strain) were found to be sensitive to high temperature. No effect of salinity on sex ratio was observed. Improving the growth of genetically male tilapia (GMT) through crossbreeding has been initiated. An initial study showed the hybrids had better growth than purebred progeny. The growth of GMT, genetically female tilapia (GFT) and mixed-sex tilapia (MST) was evaluated, (i) during a period of androgen hormone treatment designed to alter the phenotypic sex, (ii) during the post-treatment period, and (iii) during the late life stages in monosex and mixed-sex culture environments. GMT was observed to exhibit faster growth at the early ages. No anabolic effect of the hormone was observed during the period of hormone treatment and post-treatment. The sex-reversed genetic females appeared to grow better than the genetic males during the late life stages. The culture of all-female progeny appears to have great potential. A series of experiments were performed to evaluate factors affecting sex reversal. The effect of not changing the water and increasing the temperature during hormone treatment was evaluated. The possible leaching out of hormone from hormone-treated feed was also investigated. Some of the sexually undifferentiated fry reared in water previously used for hormone treatment was sex-reversed indicating that hormone residues had accumulated during previous hormone treatment. Increasing the temperature during hormone treatment was observed to improve the efficiency of sex reversal, particularly feminisation. Results showed that hormone leaches from hormone-treated feed suggesting that the observed accumulation of hormone residues could be partly due to leacheates.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available