| Summary: | 碩士 === 國立臺灣海洋大學 === 水產養殖學系 === 102 === Tilapia is one of the most important aquaculture species worldwide. Among these, unisexual male tilapia shows advantages in body size, growth rate, and simple maintenance with high economic benefits. Previously, researchers in Taiwan produced en mass mono-sex tilapia fry through interspecific hybridization between female Nile tilapia (Oreochromis niloticus) and male Blue tilapia (O. aureus). However, it was difficult to identify pure tilapia species after interspecies hybridization. Furthermore, hybridization without appropriate species management often results in decreased mono-sex fry production. In addition, the lack of proper breeding management is likely to cause inbreeding during selection and breeding. Inbreeding may cause low heterozygosity and decrease the genetic diversity of the species, thereby affecting economically significant traits. The aim of this study was to conduct DNA molecular marker-assisted identification of pure Nile tilapia species and to investigate the correlation of genetic diversity and growth traits. A total of 72 individuals from the NTOU tilapia (NT) population were used in the mitochondrial DNA D-loop PCR-RFLP analysis and 4 microsatellite markers, UNH222, UNH155, UNH172, and UNH773 were used identifying the pure Nile tilapia species. The results of present study showed that only 12 (7 females and 5 males ) individuals in the NT population were pure Nile tilapia species. The others were hybrids generated from crosses involving the Nile, Blue and Mozambique tilapia (O. mossambicus). The proportion of purebred of Nile tilapia in the NT population was only 16.7%. Twelve growth-related microsatellite markers, namely, OniPrl1-1, OniPrl1-2, UNH898, UNH934, UNH925, UNH848, UNH868, UNH130, UNH879, UNH1003, GM180, and UNH146 were used to calculate the genetic diversity and to analyze the correlation of markers and growth traits in the NT and farmed tilapia (FT) populations. The results revealed that the observed heterozygosity, the expected heterozygosity, the polymorphism information content (PIC), and the individual fixation index (Fis) in the NT and FT populations were 0.57 ± 0.14, 0.67 ± 0.08, 0.66 ± 0.08, 0.15 ± 0.18 and 0.64 ± 0.09, 0.72 ± 0.08, 0.71 ± 0.09, 0.08 ± 0.31, respectively. The genetic diversity of the NT population was lower than that of the FT population. Both populations were inbreeding and deviated from the Hardy-Weinberg equilibrium. In addition, post hoc multiple comparison of each genotype by Duncan's new multiple range test identified 11 markers that showed significant correlations with body weight (p < 0.05). Among these, UNH898, UNH925, UNH848, UNH868, UNH130, UNH879, UNH1003, and UNH146 showed highly significant correlations with body weight (p < 0.01). Similar results were found in the NT population. On the other hand, the DD type of Prl1-1, AA type of UNH130, and CD type of UNH146 showed the least suggestive correlations (p < 0.05) with body weight in the NT and FT populations. The results of the present study indicated that the establishment of the Nile tilapia pure species identification platform and the systematic genetic management scheme could contribute to species purity and maintenance of genetic diversity. These technology could improve the production of mono-sex offspring in the hybridization of female Nile tilapia and male Blue tilapia. Furthermore, these growth-related markers can be integrated with stress indicator test.
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