Assessment The Cold Tolerance Of Oreochromis Aureus And The Efficacy Of Low Temperature Breeding

For the reasons of studying Oreochromis Aureus cold tolerance capability and their breeding results, this research has carried on three different tests. And base on the comparing of the cold tolerance capability of different Oreochromis Aureus strains to assess the results of cold tolerance breeding.Testl Assessment of the cold tolerance capability of different Oreochromis Aureus strainsIn the condition of indoor artificial cooling, and at the rate of0.2℃/3h cooling to study the cold tolerance capability of three different Oreochromis Aureus strains and fifth-teen species. The results show that:the lowest lethal temperature of50%individuals (LT50) of USA strain、 xia’aol strain and Guangdong strain are respectively7.82℃、8.22℃and8.44℃;low temperature mortalities are56.76%、62.25%and79.43%;the cold tolerance capability of USA strain is better than xia’ao1strain’(P<0.05) and Guangdong strain’(P<0.05). Comparison of fifth-teen hybridization species’LT50shows that the specie which its parental is USA strain Oreochromis Aureus(?)*Egpyt strain nile tilapia(?). is8.22℃, is the lowest LT50. Correlation analysis show that all the species’LT50’s and low temperature mortalities are significantly related(P<0.05); the hybridization specie (Oreochromis Aureus(?)×Egpyt strain nile tilapia^) and its parental’LT50’s and low temperature mortalities are positive significantly related(P<0.05). In all, the USA strain has the best cold tolerance capability.Test2Assessment of the results of cold tolerance breeding of Oreochromis AureusWith the method of closure group generation breeding and low temperature breeding, for USA strain Oreochromis Aureus natural population as breeding group and by the assessment of their cold tolerance capability and growth performance to get a basic group and a core group. And the number of fish of the basic group is1129, selected rate is43.20%; the number of fish of the Po generation core group is290, the ratio male and female is1:1, selected rate is16.52%. And the number of fish of the P1generation core group is about400, are from10different families, selected rate is about25%. Base on the core group breeding, by the nest matching method has matched296families of P1generation, and seeding families are162, seeding flies are156100, the rate of success matching is54.73%; matched152families of P2generation, and Measurement the cold tolerance capability of10selected Oreochromis Aureus families show that:the average of LT50of P1generation and P2generation are respectively6.88℃and6.70℃, are respectively lower11.6%and15.8%than natural population, and their average relative survival rates are respectively higher21.1%and26.3%, and their average growth speeds are respectively higher5.23%and11.1%; and LT50of the best cold tolerance capability Pi generation and P2generation families are respectively lower14.5%and13.8%than natural population, and their average relative survival rates are respectively higher24.1%and35.0%, and their average growth speeds are respectively higherl3.5%and9.09%.The cold tolerance capability and growth performance of all the Pj generation and P2generation families and core group are higher than natural population.Test3Assessment of the cold tolerance capability of different Oreochromis Aureus familiesIn the condition of indoor artificial cooling, and at the rate of0.3℃/3h cooling to study the cold tolerance capability of different families of USA Oreochromis Aureus strains. The measurement results show that:LT50of6different families ((?)AO0107×(?)AO0107、(?)AO0117×(?)AO0133、(?)A00107×(?)AO0133-1、(?)AO0133×(?)O0117、(?)O0117×(?)AO0107、(?)AO0107×(?)AO0133-2) are respectively5.8℃、5.7℃、5.8℃、5.83℃、6.0℃and5.8℃; CDH are respectively1102.5、1130.67、1113.1092、1047.03and1092.1. Correlation analysis and multiple comparison by LT50and CDH show that family V’LT50and CDH ((?)AO0107×(?)AO0107) are respectively significantly related (P<0.01) with rest5other families, it has the poorest cold tolerance capability; and the rest5other families’LT50and CDH are not significantly related (P>0.05) with each other. All6families’cold tolerance capabilities are stable inherited and grown strengthen.