Aquatic Toxicology has come to be a new science these days and have a good scope since one or other water body is polluted by anthropogenic activities. The amount of fresh water on Earth is limited and its quality is under constant pressure as reported by Global Analysis and Assessment of Sanitation (GLAAS, 2012). The effects of different toxicants on water quality and inhabiting organisms is of major concern because the aquatic organisms particularly fishes serve as the cheap and best protein source in human diet. Freshwater is indispensable and is a vital source for life. Due to human activities the water quality is contaminated to a much extent that if it continues than we will deprive of potable water and good food source that is fishes in future. The accumulated levels of heavy metals exceeded than the recommended levels of WHO(1985-89), USFDA (1993b-93),FEPA (2003)in fishes, threatening the human health. This book, therefore, provides a base to the students of Bachelor and Master of Sciences,research scholars working on aquatic toxicology.Policy makers will also find this work useful to them.