The genomes of plant and animal species are influenced by ancestral whole-genome duplication (WGD) events, which have profound impacts on the regulation and function of gene networks. To gain insight into the consequences of WGD events, we characterized the sequence conservation and expression patterns of ohnologs in the highly duplicated activin receptor signaling pathway in rainbow trout (RBT). The RBT activin receptor signaling pathway is defined by tissue-specific expression of inhibitors and ligands and broad expression of receptors and Co-Smad signaling molecules. Signaling pathway ligands exhibited shared expression, while inhibitors and Smad signaling molecules primarily express a single dominant ohnolog. Our findings suggest that gene function influences ohnolog evolution following duplication of the activin signaling pathway in RBT.