Genetic Diversity Analysis And Growth Comparison In A Gift Strain Nile Tilapia(Oreochromis Niloticus) Population

GIFT strain Nile tilapia (Oreochromis niloticus) is a improved strain that obtained from the mixed selection based on four African origin strains (Egypt, Ghana, Keny and Senegal) and four Asian farmed strains (Israel, Singapore, Thailand and China Taiwan), by the International Center for Living Aquatic Resources Management (ICLARM). The Freshwater Fisheries Research Center of Chinese Academy of Fishery Sciences introduced60families of GIFT tilapia from the WorldFish Center in August2006. This is the first time to introduce so many families of GIFT tilapia since it was firstly introduced to China in1994. A new generation GIFT strain Nile tilapia which is the offspring of these60families after interspecific hybridization and selection shows growth advantage and potential.Microsatellite DNA, also known as simple sequence repeats (SSR), has been widely used in aquatic animal germplasm identification, genetic structure, genetic mapping construction and quantitative trait loci location.In this study,30microsatellite loci from the second-generation genetic linkage map of tilapia were used to analyze the genetic structure of the first generation GIFT tilapia breeding population. The results showed that135alleles were detected in the first generation GIFT tilapia population from30microsatellite loci, and the number of allele at each locus was from2to7, with an average of4.6. The DNA fragment length was from104bp to322bp. The average heterozygosity value was0.5872, with the average expected heterozygosity value of0.6049, and the average polymorphism information content (PIC) was0.5883. Out of30detected loci,25loci were in high polymorphism degree (PIC>0.5),4loci were in medium polymorphism degree and1locus was in low polymorphism degree. The rich polymorphic information content of the tested58fish covered almost whole families indicated high level of genetic diversity in the population. This population still maintained a high level of genetic diversity after dacades years selective breeding, and had a large selection potenetial.In addition, the comparison between different generation GIFT tilapias and between GIFT and hybrid tilapia were carried out in order to testify the selection achievement. The results showed that growth rate increased11.07%in the second generation (G2) compared with the first generation (G1) at the same culture condition, the survival rate was higher than G1, but the coefficient of variation of weight was lower than G1. The growth rate was26.6%higher in G2than the hybrid in the ponds culture, and38.7%higher in cement pools. The selected GIFT tilapia had good performances in the average body weight, feed conversion rates, absolute weight gain, specific weight gain rate, survival and seinability no matter they were cultured in earthen ponds or cement pools, while the male rate was less than the hybrid. The results indicated the success of GIFT tilapia selection.