Book excerpt: Many physiological processes are regulated by the movement of ions into and out of organs, tissues, and cells. During the past decade, a variety of new techniques and approaches have contributed to a deeper understanding of the myriad influences ions have on the function and structure of organisms. From respiration and excretion to neurological control and metabolic processing, ions and their regulation occupy a central role in physiology of fish as well as other organisms. - Comprehensive update of ionic regulation in fish - Focuses on wide variety of organ systems and the influence of ions on organ system function - Contributions from an international group