Sincere attempt have been made to make this book comprehensive. The book has been written in keeping view different diseases in fresh water fishes and birds by helminth parasites. The data and inferences presented in this book have been taken from various sources. I felt that the need of book may fulfill few sort of information about the helminth parasites to the students and researchers. Broadly, the book has been divided in four section which deals with introduction, Morphology, Histopathology, Biochemistry and Seasonal variation of helminth parasites.The subject matter has been explained with the help of finely; drown simple and well labeled diagrams.