In eukaryotic cells, intracellular transport is mediated by coated vesicular carriers. Coat proteins I (COPI) vesicles are involved in the retrograde transport from Golgi apparatus to the endoplasmic reticulum. The COPI complex is composed of ADP-ribosylation factor 1 and coatomer comprising seven subunits, termed alpha-zeta. We isolated and characterised a cDNA sequence from rainbow trout homolog to delta-subunit of COPI complex (delta-COP). Trout delta-COP gene encodes a protein of 509 aa including a characteristic Mu homology domain. Searches at the Ensemble Genome browser identified three additional teleostean delta-COP-like sequences from pufferfish, rice fish, and stickleback. Sequence identity of piscine delta-COP protein sequences is greater than 84%. Moreover, a phylogenetic analysis indicates that delta-COP protein sequences are strongly conserved among vertebrate species. delta-COP homologue is ubiquitously expressed in trout tissues. Quantitative Real-Time RT-PCR revealed that delta-COP is differentially expressed in liver and gill tissue of two rainbow trout strains, the freshwater strain STEELHEAD and the brackish water-adapted strain BORN.