Microcystin-LR: How it affects the cardio-respiratory responses to hypoxia in Nile tilapia, Oreochromis niloticus

► Effects of MC-LR on the cardio-respiratory function of Nile tilapia were analyzed. ► Exposure to MC-LR reduces metabolic rate and increases the critical O2 tension. ► The cardiac frequency and ventilatory parameters also were reduced. ► MC-LR exposure may reduce the survival chances of Nile tilapia in hypoxic environments.