The euryhaline killifish Fundulus heteroclitus lives in estuaries and
salt marshes on the eastern coast of North America. Killifish must
dynamically regulate their ion balance because of routine
fluctuations in salinity in their natural environment. This species
can tolerate changes in salinity from freshwater to nearly four times
seawater and have therefore been used extensively
to understand fish osmoregulation the mechanisms of physiological plasticity and the evolution of salinity tolerance