Cnaani, A., Institute of Animal Science, Agricultural Research Organization, P.O. Box 6, 50250 Bet-Dagan, Israel, Hubbard Center for Genome Studies, University of New Hampshire, Gregg Hall, 35 Colovos Road, Durham, NH 03824, United States
Zilberman, N., Institute of Animal Science, Agricultural Research Organization, P.O. Box 6, 50250 Bet-Dagan, Israel
Tinman, S., Central Fish Health Laboratory, Ministry of Agriculture, 19150 Nir David, Israel
Hulata, G., Institute of Animal Science, Agricultural Research Organization, P.O. Box 6, 50250 Bet-Dagan, Israel
Ron, M., Institute of Animal Science, Agricultural Research Organization, P.O. Box 6, 50250 Bet-Dagan, Israel

We searched for genetic linkage between DNA markers and quantitative trait loci (QTLs) for innate immunity, response to stress, biochemical parameters of blood, and fish size in an F2 population derived from an interspecific tilapia hybrid (Oreochromis mossambicus x O. aureus). A family of 114 fish was scanned for 40 polymorphic microsatellite DNA markers and two polymorphic genes, covering ∼80% of the tilapia genome. These fish had previously been phenotyped for seven immune-response traits and six blood parameters. Critical values for significance were P <0.05 with the false discovery rate (FDR) controlled at 40%. The genome-scan analysis resulted in 35 significant marker-trait associations, involving 26 markers in 16 linkage groups. In a second experiment, nine markers were resampled in a second family of 79 fish of the same species hybrid. Seven markers (GM180, GM553, MHC-I, UNH848, UNH868, UNH898 and UNH925) in five linkage groups (LG 1, 3, 4, 22 and 23) were associated with stress response traits. An additional six markers (GM47, GM552, UNH208, UNH881, UNH952, UNH998) in five linkage groups (LG 4, 16, 19, 20 and 23) were verified for their associations with immune response traits, by linkage to several different traits. The portion of variance explained by each QTL was 11% on average, with a maximum of 29%. The average additive effect of QTLs was 0.2 standard deviation units of stress response traits and fish size, with a maximum of 0.33. In three linkage groups (LG 1, 3 and 23) markers were associated with stress response, body weight and sex determination, confirming the location of QTLs reported by several other studies.