Family establishment and disease resistance of different families of GIFT Nile tilapia Oreochromis niloticus

The families of GIFT strain Nile tilapia (Oreochromis niloticus) were established by pair-mating and the juveniles (50~60 g) in each family were challenged by Streptococcus agalactiae (GD001 strain). According to the median lethal concentration (LC50) and infection mortality rate of each family, we evaluated the disease resistance of GIFT strain Nile tilapia to the challenge of S.agalactiae GD001 strain. The results show that: 1) 67 full-sibling families were successfully established, and 53 families (79.1%) were maintained based on their reproductive performance; 2) The LC50 of S.agalactiae GD001 strain to tilapia was 4108 cfumL-1; 3) Among the 53 families, 11 families had survival rate of over 90%, 15 families (70%~89%), 19 families (30%~69%) and 8 families (less than 30%). It is suggested that the disease resistancesof different GIFT families challenged with S.agalactiae were significantly different (P0.05).