Nikki
I have those books Terry mentioned, plus many more. You may also want to look at
Diseases in Marine Aquarium Fish, Gerald Bassleer, MS, Fish Pathology
Handbook of Fish Diseases by Dieter Untergasser (fresh water but still very helpful)
Diseases of Fishes
Book 5: Environmental Stress and Fish Diseases
by Wedemeyer, Myer and Smith
This book is just packed with valuable info you probably will not find anywhere else.
Same for this book;
Textbook of Fish Disease by E. Amalcher.
These two deal with FW but the info still applies to SW
If you want to deep-six yourself on fish and inverts, and no talk about meds;
Pathobiolgy of Marine and Estuarine Organisms by Couch and Fournie
Terry mentined Noga, that is not a cheap book $100 and Stoskopf is like $130 +, For diagnostics and treament Noga (370 p) is great but for over all info Stoskopf (900 p ) can't be beat and is why have both, they are qutie different in format.