The effects of water hardness upon the uptake, accumulation and excretion of zinc in the brown trout, <i>Salmo trutta</i> L.

Abstract

The effects of water hardness (9 and 220 mgl −1 as CaCO 3 ) upon zinc exchange in brown trout exposed to 0.77 μmol Zn 1 −1 have been investigated using artificial soft water (&lt;49.9 μmol Ca l‐1 , &lt;40.1 μmol Mg 1 −1 ) and mains hard water (1671.7 μmol Ca 1 −1 , 493.6 μmol Mg 1 −1 ) of known composition. Both hard and soft water‐adapted fish exhibited a bimodal pattern of net zinc influx. Net zinc influxes during both fast and slow uptake phases were significantly greater ( P &lt;0.001) in soft (82.9 and 6.2 μmol Zn 100 g −1 h −1 ) than in hard water (46.3 and 2.4 μmol Zn 100 g h −1 ). Zinc efflux (‐ 0.2 μmol Zn 100 g −1 h −1 ) was enhanced only in hard water during the slow net influx phase. Brown trout exposed to zinc in hard water and placed in metal‐free media exhibited a greater net efflux (‐ 25.6 μmol Zn 100 g −1 h −1 ) of the metal than did fish in soft water (‐4.2 μmol Zn 100 g −1 h −1 ) treated in the same manner. Tissue 65 Zn activities reflected both the differences in uptake and excretion rates of the metal between hard and soft water fish. During zinc exposure (0.77 μmol Zn 1 −1 ) high water hardness reduced tissue burdens of the metal by reducing net branchial influx, and enhancing efflux of the metal in hard water fish.