Effects of salinity and acetaminophen on egestion rate and movement of Poecilia reticulata

High salinity, from agricultural activities, road salt runoff, and climate change, is a problem affecting freshwater ecosystems. Elevated salinity can decrease organismal survival and growth and can alter the toxicity of pollutants. Pharmaceuticals, such as acetaminophen, enter freshwaters through non-point sources and from hospital and wastewater treatment plants effluent. Available research is limited on the combined effects of elevated salinity and acetaminophen on freshwater organisms. Our study evaluated the effects of acetaminophen (350 µg L ^− 1 ) and salinity (680 mg L ^− 1 ) on Poecilia reticulata over 96 hours. Egestion rate (mg cm ^− 1 h ^− 1 ) and movement parameters were measured following exposure. We observed significant changes in egestion rate under salinity likely due to impaired osmoregulatory mechanisms and no effect on movement. Further, there was no interaction between salinity and acetaminophen; thus, salinity did not affect acetaminophen toxicity at the concentrations tested. Our findings highlight the need of establishing threshold of salinity and pharmaceuticals to protect freshwater ecosystems and to help predict ecological impacts on aquatic organisms.