DNA presents in a cell as a functionally stable double stranded polymer. Any insults on it can cause a genetic anomaly; it is the prime interest of the genetic toxicologist to single out and study the phenomena. This monograph provides an in depth review and experimental work on the genotoxic response of sentinel species, fish, exposed to multitude of genotoxicants that presents in a tannery effluent. Moreover molecular techniques that are essential in detecting these genetic aberrations are given a wide coverage. In addition the monograph provides an insight on the essence of biological assay, comparing its validity, specificity and objectivity with that of conventional effluent monitoring. Hence the monograph would assist professionals and individuals in a regulatory scheme to widen their outlook on emerging use of eco-genotoxicological bioassays as a means of effluent monitoring and remedial activities.