Fundulus is a diverse and widespread genus of small teleost fish of North America. Due to its high tolerance for physiochemical variation (e.g. temperature, oxygen, salinity), Fundulus is a model organism to study physiological and molecular adaptations to environmental stress. The thesis focuses on patterns of protein expression in Fundulus heteroclitus and F. grandis.The patterns of protein expression were investigated using traditional methods of enzyme activity measurements and recent proteomic approaches. The findings of the study can be used to guide future studies on the proteomic responses of vertebrates to environmental stress. Chapter 2 focuses on measurement of the temporal effects of oxygen treatments on the maximal specific activities of nine glycolytic enzymes in liver and skeletal muscle during chronic exposure (28d) of Fundulus heteroclitus. The fish was exposed to four different oxygen treatments: hyperoxia, normoxia, moderate hypoxia, and severe hypoxia. The time course of changes in maximal glycolytic enzyme specific activities was assessed at 0, 8, 14 and 28 d. The results demonstrate that chronic hypoxia alters the capacity for carbohydrate metabolism in F. heteroclitus, with the important observation that the responses are both tissue- and enzyme-specific. Chapter 3 studies the effect of tissue storage on protein profile of tissues of F. grandis. The technique of one dimensional gel electrophoresis (1D-SDS-PAGE) was used to assess the effects of tissue sampling, flash frozen in liquid nitrogen versus immersion of fresh tissue in RNA later, for five tissues, liver, skeletal muscle, brain, gill, and heart, followed by LC-MS/MS to identify protein bands that were differentially stabilized in gill and liver. The study shows that, in F. grandis, the preferred method of preservation was tissue specific. xi Chapter 4 focuses on the use of advanced 2DE-MS/MS to characterize the proteome of multiple tissues in F. grandis. Database searching resulted in the identification of 253 non-redundant proteins in five tissues: liver, muscle, brain, gill, and heart. Identifications include enzymes of energy metabolism, heat shock proteins, and structural proteins. The protein identification rate was approximately 50 % of the protein spots analyzed. This identification rate for a species without a sequenced genome demonstrates the utility of F. grandis as a model organism for environmental proteomic studies in vertebrates.