Somatostatins (SSs) play important roles in the growth, development and metabolism of vertebrates. In this study, cDNAs for two unique somatostatin receptor variants were cloned and sequenced from rainbow trout. The two cDNAs, one consisting of 1755 bp and the other of 1743 bp, share 63.6% identity in nucleotide sequence and 94.1% identity in deduced amino acid sequence and presumably arose through gene duplication. Each cDNA encodes for a putative 371-amino acid somatostatin receptor (one designated sst1A and the other sst1B) containing seven transmembrane domains. Rainbow trout sst1A and sst1B have 64.4 and 65.5% similarity respectively with human sst1 and only 43-60% similarity with other subtypes. Trout sst1 mRNAs are differentially expressed, both in terms of distribution among tissues as well as in terms of abundance within selected tissues. Both sst1A and sst1B mRNAs were present in brain, stomach, liver, pancreas, upper and lower intestine, pyloric cecum, kidney and muscle, whereas only sst1B mRNA was present in the esophagus. sst1A mRNA was more abundant than sst1B in the optic tectum, whereas sst1B mRNA was more abundant than sst1A in liver. sst1A and sst1B mRNAs were equally abundant in pancreas. These findings contribute to the understanding of the evolution of the SS signaling system and provide insight into the mechanisms that regulate the expression of SS receptors.