Detection of a chromosomal region with two quantitative trait loci, affecting cold tolerance and fish size, in an F2 tilapia hybrid

We searched for genetic linkage between microsatellite DNA markers and quantitative trait loci (QTL) for cold tolerance and fish size (body weight and standard length) in two unrelated F-2 families of interspecific tilapia hybrids (Oreochromis mossambicus x Oreochromis aureus). The first experiment was based on a family of 60 fish scanned for 20 microsatellites. A second experiment was conducted with a family of 114 fish scanned for 6 microsatellites in one linkage group, in order to test for QTL found in the first experiment. This two-step experimental design was used in order to protect against false positive associations. In both families, significant associations were found for two loci within the same linkage group. The two QTL, near UNH879 for cold tolerance, and near UNH130 for body size, were estimated to be 22 cM distant from each other, with no interaction found between the two traits. One of these loci, UNH879, was also associated with sex determination. Distortion from the expected Mendelian genotypic ratio was observed for three markers: UNH130, UNH180 and UNH907, suggesting linkage with a QTL affecting survival. These results identify a chromosomal region in the tilapia genome harboring several QTL affecting fitness traits. (C) 2003 Elsevier Science B.V. All rights reserved.