Chronic effects of silver exposure on ion levels, survival, and silver distribution within developing rainbow trout (Oncorhynchus mykiss) embryos

Rainbow trout embryos were chronically exposed to silver (as AgNO3) in mode rately hard water (120 mg CaCO3/L, 0.70 tnM Cl-, 1.3 mg/L dissolved organic matter, 12.3 +/- 0.1 degreesC) at nominal concentrations of 0.1, 1, and 10 mug/L (measured = 0.117 +/- 0.008, 1.22 +/- 0.16, and 13.51 +/- 1.58 mug/L , respectively) to investigate the effects on mortality, ionoregulation, an d silver uptake and distribution of the embryo. Mortalities in the low conc entrations (0.1 and 1.2 mug/L) were not significantly different from contro ls throughout embryonic development (days 1-32 postfertilization). Mortalit ies of embryos in the 13.5-mug/L treatment reached 56% by day 32 postfertil ization (33% when accounting for control mortality), by which time more tha n 50% of surviving embryos had hatched. Accumulation of silver in whole emb ryos of 1.2- and 13.5-mug/L treatments reached the highest concentrations o f 0.13 and 0.24 mug/g total silver, respectively, by day 32, but whole embr yo silver burden was not correlated with mortality. Silver concentrations i n different compartments of the whole embryo (chorion, dissected embryo, an d yolk) were greatest just before hatch and were higher in the chorion for all experimental treatments. Up to 85% of total whole embryo silver content was bound to the chorion, which acts as a protective barrier during silver exposure. Whole embryo Na+ concentration in the 13.5-mug/L treatment was s ignificantly reduced relative to controls from days 23 to 32 postfertilizat ion, and levels in the embryo were reduced by 40% at day 32 postfertilizati on, indicating that silver toxicity in the whole embryo is associated with an ion regulatory disturbance that is similar to the acute effect of AgNO3 In juvenile and adult trout.