The series "Fish Physiology" recently celebrated its 50^th Anniversary. In total, the editors of the series have produced a total of 47 books (several volumes have two books) that contain almost 500 chapters since the inaugural volume published in 1969. The content of the "Fish Physiology" volumes has evolved over time. The initial volumes were devoted to understanding the basic mechanisms and principles of fish physiology, with a focus on a few model species and some application to natural environmental conditions. Then, as the field better understood mechanisms, the approach was broadened to not only delve deeper into system physiology (e.g., chapters in early volumes were expanded to become books), but interspecific differences in physiology were explored, permitting a more evolutionary framework. Finally, as interspecific physiological mechanisms were further resolved, it became possible to discuss physiology in light of a changing world. Thus, physiology can now inform on conservation, sustainability and management, as exemplified with the most recent volumes. This anniversary issue celebrates the series by highlighting some of the very important early work in the field that was published in the Series. In particular, we wished to (re)introduce new researchers to this research that has stood the test of time and that shaped the field. Each re-published chapter is preceded by a short review written by experts in the field to provide an overview/introduction of each selected chapter, discuss what is particularly noteworthy or important in the particular chapter, and discuss why in their opinion this chapter has become a classic in its own right and how it has inspired the field of fish physiology today?