Oxidative stress and metabolic responses to copper in freshwater- and seawater-acclimated killifish, Fundulus heteroclitus

In freshwater (FW), many of the main mechanisms of copper (Cu) toxicity have been characterized; however, toxicity mechanisms in seawater (SW) are less well understood. We investigated the effects of salinity on Cu-induced oxidative stress and metabolic responses in adult killifish, Fundulus heteroclitus. We exposed FW and SW-acclimated killifish to either low Cu (LC, 50 μg/L) or high Cu (HC, 200 μg/L) for 96 h and compared them to controls (CTRL) under the same salinities without added Cu. Cu exerted minimal influence on tissue ion levels in either FW or SW. Salinity generally protected against Cu bioaccumulation in the gills and liver, but not in the carcass. Hematocrit (Hct) and hemoglobin (Hb) levels were increased by LC and HC in both FW and SW, and blood lactate was reduced in FW-killifish exposed to LC and HC. Rates of oxygen consumption were similar across treatments. Salinity reduced Cu load in gill, liver and intestine at LC but only in the gills at HC. In general, Cu increased gill, liver, and intestine catalase (CAT) activity, while superoxide dismutase (SOD) either decreased or remained unchanged depending on tissue-type. These changes did not directly correlate with levels of protein carbonyls, used as an index of oxidative stress. Cu-induced changes in carbohydrate metabolic enzymes were low across tissues and the effect of salinity was variable. Thus, while salinity clearly protects against Cu bioaccumulation in some tissues, it is unclear whether salinity protects against Cu-induced oxidative stress and metabolic responses.