| dc.description.abstract | Oreochromis niloticus commonly known as Nile tilapia is the most cultured tilapine cichlid in
the sub-Saharan Africa. Most of the culture practices are of mixed sexes with the inherent
problem of overpopulation leading to stunted growth. Mono-sex culture of all-male
individuals is now encouraged by sex reversal through heat treatment technology. However
the method is still at development stage. The aim of the present study was to determine the
genetic basis of heat induced sex-determination in 0. niloticus as an approach towards
improving heat treatment technology and to assess the genetic variability of the invasive 0.
niloticus for conservation and management within Lake Victoria Nyanza gulf and the Yala
swamp. Juvenile 0. niloticus were subjected to heat treatment at temperatures ranging from
28°C to 36°C using 26°C as control. There was a positive correlation between treatment
temperatures and resultant male sex ratios (p<0.01). However, the survival rates of the fry
showed a negative correlation with the temperature (p<0.01). The optimal temperature that
provided for optimal sex reversal towards males and survival rates of the fry was found to be
36± 1°C, which gave a male proportion of 86.31 % and fry survival rate of 65.25%. To study
genetic basis of heat induced sex determination three sex linked markers UNH846, Abur36
and AburlOO were selected, genotyped and sequenced. The marker Abur36 identified the sex
of 95% of the heat induced individuals. The putative function of this gene indicated that the
gene could be a male biased hormone producer or transcriptional factor whose activity is
influenced by elevated temperature within a narrow range before the onset of the temperature
sensitive gonadal sexual differentiation. Determination of the genetic diversity and purity of
0. niloticus was carried out based on eight microsatellite markers and mitochondria DNA
control region and compared with that of 0. esculentus. No admixture between the two
species was detected. However there were low levels of nuclear admixture primarily from 0.
niloticus to 0. esculentus. Genetic diversity of 0. niloticus (h =0.829, 1t: = 0.008) was higher
than that of 0. esculentus (h = 0.816; 1t: = 0.004). All populations of the two species retained
unique haplotypes and alleles in their respective lakes. Pairwise FST values for population
differentiation of both species were all highly significant (P < 0.001). Therefore the four
populations of 0. niloticus are potential sources of broodstock choice from which all-male
fingerlings could be produced using heat treatment technology. | en_US |
