The cytochrome P450 1 (CYP1) family has expanded with the addition of the CYP1B and CYP1C subfamilies. We recently identified a new CYP1 subfamily in zebrafish, CYP1D, with a single gene, CYP1D1. Here we examined sequences found in other fish genomes, i.e., stickleback (Gasterosteus aculeatus) and medaka (Oryzias latipes), for similarities among fish CYP1D1 genes. The full-length deduced amino acid sequences for CYP1D1 in these two species averaged about 43% identity to the CYP1As, but nearly 50% when sequence alignment ambiguities were masked. CYP1D1 has seven exons, similar in size and position to the exons in CYP1D1 and CYP1A in zebrafish. However, the intronic distances were substantially smaller in the medaka and stickleback. There also were differing numbers of putative xenobiotic response elements in the CYP1D1 of the various species. Whether the stickleback or medaka genes are inducible by aryl hydrocarbon receptor (AHR) agonists is yet to be determined.