Teleost fish that inhabit in an aquatic environment always face osmotic problems. Freshwater fish face a hypoosmotic situation, namely, water flows into the fish body while ion flows out of it. Fish living in seawater, on the other hand, have to manage water loss and salt load in a hyperosmotic environment. In such a circumstance, osmoregulatory organs composed of the gill, kidney, intestine and bladder are importantly involved in adapting to a wide variety of surrounding salinity. This project, therefore, aims to identify novel principal genes contributing to such fish osmoregulation through transcriptome analysis, especially focusing on kidney and intestine.