The threat of pollutants mixtures on freshwater fishes in Sri Lankan lotic ecosystems under changing climate: a review of current status and future research perspective

Multiple point and nonpoint sources add complex mixtures of pollutants that may pose detrimental impacts on freshwater fish. These pollutants include metallic and nonmetallic inorganic ions and an array of organic compounds. Climate-related scenarios and a mixture of contaminants entering riverine ecosystems have impacted many endemic freshwater fish species in Sri Lanka. The present research aims to identify morphological, physiological, and behavioral changes upon exposure to xenobiotics and to predict the influence of climate on these fishes. We discussed the biomarker responses of feral fish, combined with their physicochemical characterization. Moreover, the discussion emphasized empirical evidence from controlled laboratory experiments. Together, these elements were used to interpret the possible future impacts of climate change on the fish in lotic ecosystems. The effects of nanoparticles, microplastics, pharmaceuticals, and endocrine disruptors, and their interplay with climate-related physicochemical variation, have been identified as a research gap. The primary research directions for the future include establishing multi-stressor experimental frameworks that integrate a mixture of xenobiotic exposures of indigenous fishes. The development of standardized biological monitoring protocols that simulate real-world conditions in lotic ecosystems is crucial. Introduction of scientific, evidence-based, robust, and urgent legislative reforms to regulate cumulative pollution may provide a strong legal framework to prevent devastating impacts on freshwater fishes in lotic ecosystems in Sri Lanka.