Characterization of gene expression in tissues important to osmoregulation in the Atlantic stingray, H. sabinus. This will be done for the forms of H. sabinus that are restricted to freshwater and those that live exclusively in marine environments. Sequences will be used to identify candidate biochemical pathways associated with the genes that are differentially expressed by the individuals living in these habitats. This data allows for a better understanding of the physiological changes that are involved in the transition between marine and freshwater environments and the role that different tissues play in the change.