Composite interval mapping reveals three QTL associated with pyloric caeca number in rainbow trout, Oncorhynchus mykiss

The pyloric caeca of fishes are a major site for nutrient digestion and absorption. Some studies have reported an association between increased caeca number, improved feed efficiency and faster overall growth in rainbow trout. However, little is known concerning the genetic basis underlying pyloric caeca development in any fish species. We have identified two clonal rainbow trout lines that differ in pyloric caeca number. Doubled haploid progeny produced from an F 1 hybrid of these lines were used to evaluate the possibility of joint segregation of pyloric caeca phenotype with 330 amplified fragment length polymorphic (AFLP) markers and 39 microsatellites genotyped in 54 individuals. A genetic map has been constructed based on these genotypes and composite interval mapping revealed three major quantitative trait loci (QTL) associated with pyloric caeca number. These QTL respectively explain 19.2%, 18.6% and 13.5% of the variation in pyloric caeca number observed within the doubled haploid progeny. Because these QTL span 3 separate linkage groups, our results demonstrate the phenotype of pyloric caeca number is a polygenic trait in rainbow trout.