Analysis Of Growth Performance And Genetic Variation Of The Recent Selected Generations Of New Gift Strain Nile Tilapia (Oreochromis Niloticus)

1. Growth performance among the lasted selected generations of F₁₂-F₁₄ of NEW GIFT strain Nile tilapia(Oreochromis niloticus)was compared.Growth performance of NEW GIFT strain Nile tilapia(Oreochromis niloticus)from 12th to 14th was compared at Nanhui Experimental Station for Fish Germplasm of Shanghai Ocean University, the experiment date from Jul.28 to Oct.12, total of 74 days in 2009 year and date from Aug.6 to Oct.9, total of 64 days in 2010 year, respectively. The results showed that:(1)The body weights of F₁₂-14 were 160.16g,175.57g,125.94g,137.44g respectively at the end of the experiment,namely F₁₃(2009)> F₁₂(2009), F₁₄(2010)> F₁₃(2010).(2) The averages of daily body weight gain of F₁₂-14 of the total experiment periods were 1.76g/d,1.93g/d,1.73g/d,1.96g/d respectively, namely F₁₃(2009)>F₁₂(2009)and F₁₄(2010)>F₁₃(2010), among them F₁₃(2009)was 9.66% higher than F₁₂(2009) and F₁₄(2010)was 13.29% higher than F₁₃(2010); after emending bias, F₁₃(2009)was 6.77% higher than F₁₂(2009)and F₁₄(2010)was 7.30% higher than F1(32010).(3)The variation coefficients of body weight of F₁₂-14 were 0.2153,0.1844,0.2064,19.69 respectively at the end of the experiment, namely F1(32009)<F₁₂(2009)and F1(42010)<F1(32010), among them F1(32009)was 14.35% lower than F1(22009)and F1(42010)was 4.60% lower than F₁₃(2010).2. Genetic variations among the lasted selected generations of F11-F₁₄ of NEW GIFT strain Nile tilapia(Oreochromis niloticus)by SSR analysisSimple Sequence Repeats(SSR)marker analysis was used to measure the genetic structure and genetic differentiation of four successively selected generations(F11,F₁₂,F₁₃,F₁₄)of NEW GIFT strain Nile tilapia(Oreochromis niloticus). The results showed that: (1)total of 89 alleles(115～270 bp)were found among the four populations of 120 individuals with 15 polymorphic microsatellite loci. (2)The mean number of effective alleles of four generations ranged from 2.86 to 3.26, decreased by generation by generation, but no significant differences among generations(t test, P>0.05). (3) The expected value of mean heterozygosity varied from 0.638 4 to 0.676 0 in four selected generations, decreased by generation by generation, but no significant differences among generations(t test, P>0.05). (4) The average polymorphism information content varied from 0.570 8 to 0.626 4 in four selected generations, which indicated 15 polymorphic microsatellite loci contain higher polymorphism information conten in the four generations of NEW GIFT strain Nile tilapia(Oreochromis niloticus). The genetic parameters above all indicated the same tendency that they have been steadily decreasing with the increasing of selected generations, which proved that the purifier experience of NEW GIFT strain Nile tilapia(Oreochromis niloticus)was still continuing in the course of long-term selective breeding. On the other hand, pair-wise FST values between the arbitrary two generations ranged from 0.016 7 to 0.0547, which indicated that the four selective breeding generations generated a certain extent genetic differentiation, but the genetic differentiation level was very small.3. Genetic variations among the lasted selected generations of F10-F₁₃ of NEW GIFT strain Nile tilapia(Oreochromis niloticus)by SSR analysisSimple Sequence Repeats(SSR)marker analysis was used to measure the genetic structure and genetic differentiation of four successively selected generations(F10,F11,F₁₂,F₁₃)of NEW GIFT strain Nile tilapia(Oreochromis niloticus). The results showed that: total of 78 alleles(100～295 bp)were found among the four populations of 120 individuals with 13 polymorphic microsatellite loci. The mean number of effective alleles of four generations ranged from 2.84 to 3.27, the average polymorphism information content and the expected value of mean heterozygosity varied from 0.627 1 to 0.676 2 and from 0.567 6 to 0.622 9 in four selected generations, respectively. Three genetic parameters all indicated the same tendency that they have been steadily decreasing with the increasing of selected generations, which proved that the purifier experience of NEW GIFT strain Nile tilapia(Oreochromis niloticus)was still continuing in the course of long-term selective breeding. On the other hand, pair-wise FST values between the arbitrary two generations ranged from 0.019 07 to 0.133 54, which indicated that the selective breeding generations also generated moderate genetic differentiation. The above results showed that our applied breeding technique strategy (synchronized selection at Yellow River, Yangtze River and Pearl River ecosystems, exchange periodically, keep effective breeding number, as well as strict super-fish four-steps selection proceeding)for the NEW GIFT strain Nile tilapia ( Oreochromis niloticus ) could make the selective breeding populations maintain abundant genetic variation, which would be beneficial to the sustainable development of long-term selective breeding.