Date of Graduation


Document Type


Degree Name

Doctor of Philosophy in Cell & Molecular Biology (PhD)

Degree Level



Biological Sciences


Christian Tipsmark

Committee Member

Mack Ivey

Second Committee Member

Ralph Henry

Third Committee Member

Ines Pinto

Fourth Committee Member

Wayne Kuenzel


Euryhaline, Gill, Medaka, Osmoregulation, Rainbow Trout


Euryhaline fishes are capable of adapting to a wide range of salinities such as freshwater, brackish water or seawater. Through the combined effort of the gill, kidney and intestine, they are able to osmoregulate to maintain a constant internal hydromineral balance. As the gill is in direct contact with the external environment, it is continuously working to maintain ion and acid/base balance, gas exchange and eliminate nitrogenous waste. Fish in freshwater are subjected to osmotic water gain and diffusional ion loss across the gill and experience the opposite in seawater. Therefore, the gill exhibits extreme plasticity when experiencing a change in external salinity. Osmoregulation in fishes is controlled mainly by the endocrine system. Prolactin is a freshwater-adapting hormone as it decreases epithelial permeability and increases ion-retention in osmoregulatory tissues.

This dissertation examines the osmoregulatory function of the gill in two euryhaline teleosts, the Japanese medaka (Oryzias latipes) and rainbow trout (Oncorhychus mykiss). Gill of medaka exposed to seawater and freshwater were used to observe the effect of salinity on the expression of key ion transporters. Hormone in vitro studies were performed to understand the mechanism of prolactin-induced expression of the Na+, Cl- cotransporter in medaka gill. Finally, rainbow trout were subjected to ion poor water to expand our understanding of ion retention and ionocyte re-uptake function in a salmonid species.

Furthermore, several human diseases are related to (dys)function of osmoregulatory proteins including cancers, inflammatory bowel disease and chronic kidney disease. Because of the adaptability of the gill epithelia, euryhaline teleosts represent a unique model that may help us understand pathologies in human diseases related to epithelial dysfunction. The endocrine system of teleosts is also analogous to the human endocrine system and is therefore valuable to better understand hormone-linked diseases in human such as breast cancer, diabetes and atherosclerosis. The experiments performed in this dissertation demonstrate the ability of euryhaline teleosts to provide an alternative model to study human diseases.