{PDF} The Diversity of Fishes: Biology, Evolution, and Ecology Gene Helfman, Bruce B. Collette, Douglas E. Facey, Brian W. Bowen

One of the best textbooks on fish today. Gives a great overview of all the relevant topics going into detail in the places where it is best needed. If you want to know anything about fish this is the perfect place to start and if you are going to be teaching a class on fish, this is the textbook for you!