Lorenz Hauser is a geneticist who uses molecular markers to peer into the lives of fishes. His investigations vary in their levels of intimacy: he has looked at everything from the overall population dynamics of marine fish species, to the genetic identification of populations and individual relatedness of fish. Using genetic parentage tests, he even measures the reproductive success of individual salmon in Alaskan streams. The breadth of his pursuits—he has worked in both freshwater and marine systems in the Old and New World—is guided by his desire to find the model system best suited to a particular question, all of which will help promote sustainable fisheries use.