Salinity Tolerance Of Northern Redbelly Dace, Phoxinus eos, As Assessed By A 96-Hour Acute Toxicity Test

Abstract

Saline seeps are a known environmental hazard in eastern Montana. Identifying the salinity threshold value for fish using a 96-hour acute toxicity test will allow fish salinity tolerance to be taken into account when biotic integrity is used to determine the health of a waterbody. Acute toxicity tests were run 10 fish per 8 gallons of test solution in glass aquaria. The test solution was made using Na2SC>4 dissolved in carbon filtered city water and was renewed after 48 hours. Mortalities were counted and removed every 6 hours for the first 24 hours and every 12 hours there after. Results obtained from the 96-hour acute toxicity test determined the LC50 range to be 10-20 g/L using the binomial method. The geometric mean being 14.1 g/L. Results from a follow up experiment showing 100% mortality at 13 g/L lead to the conclusion that the actual LC50 lies below 14.1 g/L. The calculated LC50 value of 14.1 g/L leads to the conclusion that northern redbelly dace are a salt tolerant species well adapted to the saline waters of eastern Montana. Affected streams in eastern Montana that have salinity levels regularly approaching 9 g/L are approaching toxic levels.