Estuaries are highly dynamic environments where rapid changes in salinity can place significant physiological and behavioral stress on fishes. This research will investigate how short-term, ecologically realistic salinity fluctuations affect the welfare of estuarine fishes using non-invasive indicators such as waterborne cortisol, metabolic rate, exploration, shoaling behavior, and decision-making. Focusing on two locally abundant species (the sheepshead minnow, Cyprinodon variegatus and the sailfin molly, Poecilia latipinna) across juvenile and adult life stages, this project aims to develop practical, transferable tools for assessing fish welfare in the wild and to better understand how environmental variability influences the lived experiences of aquatic animals.