There is a current biodiversity crisis as the species diversity and abundances of many species decline in nature. The three classes commonly called fishes include more species of vertebrates than all other classes combined. Fishes also have a higher rate of endangerment than all other classes of vertebrates, due to human use of aquatic resources. Ecology of Fishes is a course for juniors and seniors that focuses on the dramatic interaction between fishes and their habitats, as a driver of this biodiversity crisis. The course covers: physiological, behavioral, and numerical responses of fishes to biotic and abiotic factors; the relationship between environmental factors and fish energetics, growth, survival, behavior, and reproduction; adaptations of fish for survival under different environmental constraints in major habitat types; and the role of humans in fishery declines and fish conservation.