Individual and combined effects of copper and parasitism on osmoregulation in the European eel Anguilla anguilla

► We combined Cu2+ contamination, parasite infestation and salinity challenge on eels. ► Osmoregulation was unaffected in close to isotonic and hypertonic salinities. ► At 5 ppt, contaminated eels to Cu2+ and Anguillicoloides crassus show osmoregulatory disturbances. ► The combined stress seems to exert a synergistic effect at low salinity.