Daniel Gomez Isaza

Aquatic habitats encompass some of the most complex and dynamic environs on earth, leaving fish to navigate multiple, interacting stressors. Fish regularly contend with shifts in key environmental conditions in combination with biotic challenges and anthropogenic pressures. Stressors are becoming more numerous and severe owing to human pressures, and multi-stressor studies are critical to building an understanding of how fish physiology is affected by multivariate phenomena, like climate change. In this article, we explore how fish physiologically respond to multivariate changes in their environment, paying particular attention to non-additive stressor interactions where “ecophysiological surprises” are revealed.

Nitrate is a natural and important component of freshwater ecosystems. Yet, human activities, such as the extensive use of fertilizers, urban wastewater, and aquaculture operations, have significantly increased the concentration of nitrate entering freshwater environments. Nitrate concentrations can nowadays be 10 to 100 times above preindustrial levels, and elevated nitrate concentrations are expected to cause severe consequences to aquatic life. However, the responses of freshwater life to elevated nitrate concentrations are mixed, with some animals showing severe signs of toxicity while others appear unaffected by nitrate, even at extremely high concentrations. This chapter describes the main toxic actions of nitrate to aquatic life and provides a summary of sublethal effects (e.g., impacts on growth, development, histopathology, and endocrine disruption). This chapter also examines how nitrate toxicity is mediated by other environmental variables, such as water temperature, salinity, and other pollutants, to affect aquatic fauna. Finally, this chapter concludes by directing future research on the effects of nitrate on aquatic fauna.