Humanity today is experiencing a dramatic shift to urban living. Local urban environmental stressors and global ones are combining to accelerate the rates of degradation of different marine, terrestrial and freshwater ecosystems worldwide. In the tropical regions, especially in the Caribbean natural habitats can be disturbed by human activities often more rapidly and persistently. As natural landscapes are altered by human disturbances, the health of streams and their fauna are increasingly at risk. Puerto Rico is a small island with a high population density and growing rate of urbanism that is driving a continual conversion of land to anthropogenic uses, increasing the accumulation of contaminants in water resources. An increasing number of chemicals liberated into the environment through human activities have demonstrated potential for disruption of biological processes critical to normal growth and development of wild species. So far, it is not known if the introduction of different types of contaminants into water bodies and urban development has the potential of altering the physiology, behavior and nervous system of aquatic animals. Organism responses vary by assemblage group, and aquatic macro-invertebrates often show the highest sensitivity to urbanization. Our study species Macrobrachium carcinus is the largest freshwater prawn that inhabits the rivers of Puerto Rico. Therefore, since it is known that macro-invertebrates are sentinel species, sensitive to contaminants, and environmental variables, it is thus a good candidate to explore if water contaminants from urban rivers can affect population rates and different aspects of neural function, including activity, and interactive behaviors. We hypothesized that anthropogenic activities near Puerto Rican urban watersheds are associated with changes on relative population density, and impairment on interactive behaviors, and general activity of freshwater prawn species. Effects of environmental contaminants can be studied at various levels of organization, including biochemical and cell levels, the level of individual organisms, and the population and community level. The results from this project will contribute towards the knowledge base of our understanding on behaviors, neural responses and management of Puerto Rico stream prawn´s communities and different levels of urbanism; (2) evaluate the effect of specific pollutants found in urban streams on the general activity; and (3) determine the effects of urban water chemicals on agonistic behaviors of adult Macrobrachium prawns.ecosystems. To achieve this goal three primary research objectives were postulated: (1) quantitatively determine differences in the relative abundance of individuals in four rivers with different levels of urbanism; (2) evaluate the effect of specific pollutants found in urban streams on the general activity; and (3) determine the effects of urban water chemicals on agonistic behaviors of adult Macrobrachium prawns.