Sex determination in Nile tilapia, Oreochromis niloticus: gene expression, masculinization methods, and environmental effects Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/gm80hz084

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  • Sex differentiation in fish is a labile process that allows sex inversion in several species. The inherent capacity of fish germ cells to differentiate into oocytes or spermatocytes constitutes a key factor allowing for functional sex inversion. This thesis set out to determine the mechanism involved in steroid-induced sex differentiation of Nile tilapia, Oreochromis niloticus, by searching for differential expression of unique genes during the process. In addition, the studies documented the persistence of methyltestosterone (MT) in the environment after oral administration, and investigated the capabilities of short-term immersions in steroids for masculinizing tilapia fry as an alternative method. A significant leakage of MT to the rearing water and its subsequent accumulation in the sediments was detected after oral administration of the steroid. In addition, evidence was found for a significant effect of environmental conditions on the masculinizing efficacy of oral administration of steroids. Low levels of masculinization were obtained when MT was allowed to remain in the system. Results from short-term immersions in steroids indicated that the labile period for masculinization by immersion of Nile tilapia fry reared at 28°C occurs between 11 and 16 days post fertilization (dpf). Two three-hour immersions in trenbolone acetate at 11 and 13 dpf yielded the highest number of males. Time of immersion, length of the treatment, dosage, density, solvent vehicle, and number of immersions significantly affected the outcome of immersion trials. Heterogeneity of developmental stages, developmental rate, and sensitivity of progeny to steroids may play important roles in the efficacy of immersion treatments. The expression of unique mRNAs during the process of sex inversion was identified through the use of suppression subtractive hybridization. This technique allowed for the sequencing of 165 clones from which 61 proteins have been identified. A significant number of these genes seem related to the anabolic effects of trenbolone acetate. In addition, 12 genes were identified that are related to reproductive tissues; seven of which have unique or enriched expression in the testes. Some of the genes and protein products that have been identified are linked to gonadal development and testicular protein synthesis in other species.
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  • description.provenance : Approved for entry into archive by Patricia Black(patricia.black@oregonstate.edu) on 2012-08-29T20:27:45Z (GMT) No. of bitstreams: 1 SanchezWinfridoMContreras2001.pdf: 7184411 bytes, checksum: c7db51c3ef8eeebf46f09d3ae32a9590 (MD5)
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  • description.provenance : Approved for entry into archive by Patricia Black(patricia.black@oregonstate.edu) on 2012-08-29T20:31:46Z (GMT) No. of bitstreams: 1 SanchezWinfridoMContreras2001.pdf: 7184411 bytes, checksum: c7db51c3ef8eeebf46f09d3ae32a9590 (MD5)
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