This introduction to conservation medicine in wild fish will discuss how basic principles of fish physiology contribute to the success or failure of some species when faced with certain obstacles such as dams and drought. The application of veterinary medicine in these scenarios is quite different from that considered in the clinical setting and requires an approach more akin to herd health management rather than treating an individual fish. Some basic principles of conservation biology will also be introduced such as genetic bottlenecks and how that can impact health and survival in wild populations with some specific real-life examples.