IDENTIFICATION OF 2 QTL INFLUENCING UPPER TEMPERATURE TOLERANCE IN 3 RAINBOW-TROUT (ONCORHYNCHUS-MYKISS) HALF-SIB FAMILIES

We searched for linkage among 24 polymorphic loci (allozymes, RAPD, mi crosatellites) in three half-sib backcross families of rainbow trout ( Oncorhynchus mykiss) produced by crossing strains divergent for the qu antitative trait of upper temperature tolerance. Seven significant and two suggestive pairwise linkage associations between molecular marker loci were observed involving 14 loci clustered into four linkage grou ps. The association between a pair of allozyme loci (sIDHP-3 and mMEP -2) has been reported previously. Recombination rates varied greatly between the sexes and families. Two quantitative trait loci (QTL) were mapped by detecting a significant association between variance in upp er temperature tolerance and alleles at the microsatellite loci Omy325 UoG and Ssa14DU. The two QTL appear to reside in different linkage gro ups and account for approximate to 13 per cent and 9 per cent of the o verall additive genetic variance in upper temperature tolerance. No si gnificant interaction was detected between Omy325UoG and Ssa14DU sugge sting that the effects of the QTL are additive.