Many species of Fundulus have been used extensively as bait fish, but perhaps their best known use is in the laboratory. Beginning in the 1800s, the mummichog (F. heteroclitus) was used to study fish embryology. The transparent eggs were stripped of their protective covering, opening a window on the developmental process and allowing easy manipulation with a variety of chemicals to assess endocrinological and biological responses. Capitalizing on the ability of these fish to withstand a wide range of temperatures and salinities, and its natural distribution near pollution sources, the mummichog also became the main study animal for intertidal and nearshore pollution tolerance.
Other experiments have used killifish and mummichogs to test learning in fish (they are able to navigate a simple maze), examine pigmentation and the function of chromatophores in response to different physical and chemical stimuli, chemical responses allowing survival at sub-zero temperatures, and most recently in determining population stability in response to environmental stresses.
Other recent efforts have focused on two different extremes: 1) use of the hermaphroditic killifish (Rivulus marmoratus) from Florida as well as other killifish species as a biocontrol agent for reducing populations of mosquito larvae and eggs; and 2) as part of the reestablishment of endangered populations of the Desert pupfish (Cyprinodon sp.) species in the California deserts. Both sets of experiments have important impacts on land use planning and local environmental stability.
While few of the many species of killifish are considered rare or endangered, it was not until the 1960s that a technique for captive rearing was refined and the removal of thousands of fish from the wild discontinued. Even today, sampling of wild populations is still conducted fairly regularly in order to further understanding of their remarkable tolerance ranges.