The Impact of Freshwater Salinization on the Osmoregulatory Physiology of Mayfly Nymphs (Hexagenia Rigida)

Freshwater (FW) salinization (the accumulation of salt in FW), is an environmental issue which threatens the health of FW ecosystems worldwide. This study used FW nymphs of the mayfly Hexagenia rigida, to provide a first examination of the effect of salinization on physiological mechanisms of ion transport in this important North American FW invertebrate. Following exposure of mayfly nymphs to sub-lethal levels of salt (7 days in 7.25 g/L NaCl) alterations in morphology and function of ion regulatory organs were found. The enigmatic tracheal gill became an ion secretory organ, instead of acquiring ions as it normally does in FW and the urine producing excretory system of H. rigida reduced salt reabsorption rates. Data indicate that ion regulatory machinery of H. rigida can reorganize in response to low levels of salt contamination, but these alterations are likely to come at a cost because ion transport mechanisms are not functioning normally.