Abstract: The method of closure group generation breedingand low temperature breeding was conducted in this paper.Egyptian strain of Nile tilapia naturalpopulation was selected as breedinggroup,by assessing their cold tolerance capability and growth performance,a basic group and a core were obtained.The number of fish in the basicgroup is 1 180,selected rate is 30.50%;the number of fish in the P₀ generationcore group is 292,the ratio male and female is 1∶1,selected rate is 16.48%.Andthe number of fish in the P₁ generation core group is about 400 from 10different families,selected rate is about 25%.Base on the core group breeding,by the nest matching method,283 families of P₁ generation have been matched,andseeding families are 137,seeding flies are 135 550,the rate of success matching is48.41%.And 91 families of P₂ generation have been matched,and seeding familiesare 42,seeding flies are 30 400,the rate of success matching is 46.13%.The coldtolerance capability of 10 selected Oreochromis aureus families show that:theaverage of LT₅₀ of P₁ generation and P₂ generation are 8.07 °C and 7.75 °C,which are 7.88％ and 13.98％ lower than the naturalpopulation,where as their average relative survival rates are 21.52% and 26.35％ higher,and their average growth speeds are 9.77％ and 18.90％ higher;LT₅₀ of the best cold tolerance capability P₁ generation and P₂ generation families are 9.13％ and 18.98％ lower than the natural population,while their average relative survival rates are 25.29％ and 30.34％ higher,and their average growth speeds are 15.87% and 33.00％ higher.The cold tolerance capability and growth performance of all the P₁ generation and P₂ generation families and core group are higher than the natural population.

Key words: Egyptian strain, Nile tilapia, cold tolerance capability, family breeding, assessment