The disruption of sodium balance in brook charr, Salvelinus fontinalis (Mitchill), by manganese and iron

Abstract

A primary toxic action of manganese to brook charr, Sulvelinusjonfinalis, at concentrations near or above the 96 h LC 50 was the disruption of sodium regulation. Body and plasma sodium concentrations of brook charr declined by 52 and 40%, respectively, during exposure to 10.9 mM manganese (in 250 PM CaCI), and all fish died within 36 h. Sodium balance was less severely affected by 2.7 and 5.5 mM manganese. An increase in the external calcium concentration from 0.05 to 1.0 mM raised the LC 50 for manganese from 4.9 to 5.8 mM, and a further increase to 2.5 mM calcium almost doubled it to 10.2 mM. An examination of stable manganese uptake by the gills revealed that accumulation was inversely correlated with body sodium concentration (r =−0.77). Radioactive J4Mn entered the bloodstream in low levels and accumulated in the liver. Thus manganese may have systemic effects as well as those attributable to surface binding on the gill. Studies of the mechanism ofdissolved iron toxicity were less conclusive, but it did not appear to involve extensive disruption of sodium balance. There was about a 15% drop in body sodium concentration when the trout were exposed for 48 h to the 96 h LC 50 level of iron, but plasma sodium was unaffected. Also, an iron concentration at twice the LC 50 did not escalate the loss of body sodium, and increasing the water calcium concentration did not raise the LC 50 .