Response of the early developmental stages of hatchery reared salmonids to major ions in a simulated mine effluent

In response to a potential revision by the state of Alaska to increase discharge limits for total dissolved solids (TDS) in the mining industry, we studied various life stages of hatchery reared salmonids exposed to the major ions in a simulated mine effluent at concentrations of salts up to 2500 mg l− 1. Effects depended on the developmental stage and the exposure period. For short term (24- to 96-h) exposures the fertilization stage was most sensitive. Fertilization success was reduced with TDS as low as 250 mg l− 1. A two-minute exposure to elevated TDS during fertilization was long enough to have deleterious effects on both fertilization success and later development. Embryos exposed to the simulated mine effluent continuously from just after fertilization through to swim-up had high post-hatch mortalities. Thus there may be at least two separate mechanisms of toxicity: an acute response at the moment of fertilization, resulting in low fertilization success, and a response to long-term exposure through swim-up, manifested by mortalities at the alevin stage. Sensitivity to dissolved salts with respect to fertilization success varied among different species of salmonids. Chinook, pink, and coho salmon were most sensitive, and Arctic charr were least sensitive to elevated salts. Specific ion tests indicated that Ca2+ was a major contributor to decreased fertilization. We suggest that the current Alaska water quality standards of 1000 mg l− 1 for TDS should not be increased and may be too high for some species. In addition, salmonid fertilization trials may be an appropriate, relatively quick, assay for setting site-specific TDS contamination discharge limits.