Theses and Dissertations

Title: Sex determination and inheritance of sex ratio in families of Oreochromis niloticus

Name: Carpenter, Robert Harper

Degree: MS

Chair: Ronald P. Phelps


University: Auburn University

Location: Auburn, Alabama

Date: 2002

Pages: 0

Keywords: Nile tilapia,sex determination,inheritance of sex ratio,impact of water temperature


Inheritance of sex ratio was studied using three strains of Oreochromis niloticus progeny sets from nine individual pair spawns, designated as families, from April to October of 2000. Five males were placed in hapas with half the females from their family and were allowed to spawn during the summer months. Ten sets of progeny from each family, eight from Family VI, were collected after at least sixty days of grow-out. Sex ratios of all 88 progeny groups were determined by microscopic examination of gonads. Sex ratio of each spawn was compared to that of the parent family, family mean, and population mean using Chi-square tests. Of the nine families, four produced progeny where 100% of the ten sets were significantly different from the parent ratio (P < 0.05). Of the other five families, four had 40 to 90% of the progeny sets different from the parent while Family VIII only reported 10% of the sets to be significantly different. Results of progeny sets when compared to the family mean, mean proportion of males for all that families spawns, revealed three families where 10% of the progeny sets were significantly different. The remaining families revealed 20 to 50% of progeny sets different from the family mean. Similar differences were found when comparing each spawn to the population mean. Calculations for heritability of sex ratio revealed an h2 value of -0.09 with an R2 value of 0.04. Results suggest sex ratio is not an inherited traits. A temperature study was also performed on spawns from three families to determine the effect of environment on sex determination. Spawns were separated into equal groups at swim-up and one group was reared in temperature controlled aquaria at 35±1C for 30 days and the other at ambient temperature averaging 29±1C. High temperature skewed the sex ratio to male in two of the three families tested giving evidence that there was an environmental component in sex determination. This effect, however, is not always expressed.

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