This book is about the various fish diseases especially in the fresh water condition of Himalayan region of Uttarakhand State. It is actually a research report after extensive literature survey and personal field experience from the Uttarakhand on the given topic. This book is aimed to provide detail scientific information on the fish disease for the university students, various research scholars and will also be helpful for the future scientific study in this field. This research will be useful to establishing the ecological relationship between fish disease and the ecosystem, which will lead to sustainable ecosystem development.