An aquatic animal is a vertebrate or invertebrate animal, which lives in water. They can be classified as fresh water or marine aquatic animals. The animals inhabiting salt-water ecosystems include corals, echinoderms, cephalopods and sharks. Fresh water ecosystems comprise of lake, river and wetland ecosystems. The salinity, nutrient levels, water depth, flow, etc. influence the aquatic ecosystem. They are characterized by low oxygen levels and slow diffusion of oxygen and carbon dioxide. Aquatic organisms exhibit a range of physiological and morphological adaptations that allows them to thrive in such environments. This book elucidates the concepts and innovative models around prospective developments with respect to the biology and ecology of aquatic animals. It consists of contributions made by international experts. It will serve as a valuable source of reference for marine biologists, ecologists, environmentalists and other professionals involved in this area of study.