Minnows can acclimate to total residual chlorine

Abstract

AbstractObservations in a chlorine‐contaminated stream in eastern Tennessee revealed several species of fish in areas where total residual chlorine (TRC) concentrations were often great enough to be lethal, based on the results of other studies. We used in situ and laboratory experiments to test the hypothesis that minnows could acclimate to TRC. Acclimation was assessed by time‐to‐death for fish exposed to a single lethal regime of TRC. In in situ experiments, striped shiner and central stoneroller minnows collected from East Fork Poplar Creek at a TRC‐contaminated site and a site farther downstream, where TRC was below detection, were caged at sites in the stream where TRC concentrations were either nil or great enough to be lethal. At the cage with high TRC, minnows collected from the “TRC‐contaminated” site survived two to four times longer (15.8 h vs. 6.1 h) than the same species from the “TRC‐free” site. In laboratory experiments, golden shiner minnows were exposed to TRC in a stepwise increasing concentration regime (0.04 mg/L during week 1, 0.08 mg/L during week 2, and 0.12 mg/L during week 3) before being challenge‐tested with a lethal concentration of TRC. Minnows that had been previously exposed to TRC survived longer than controls in each test, and the magnitude of the mean time to death increased as the TRC concentration and duration of exposure increased (1.2‐, 2.5‐, and 3.9‐fold increases for weeks 1, 2, and 3, respectively). Another experiment with golden shiner minnows showed that a 21‐d exposure to TRC at a low concentration (0.04 mg/L) only slightly increased their tolerance to TRC. Thus, several minnow species apparently can acclimate, fairly rapidly, to TRC. This study may help explain why fish kills are less common than expected in TRC‐contaminated streams.