Responses of several fish species to pH gradients

Abstract

The responses of 11 fish species to a continuous pH gradient (usually pH 4–10) were observed to obtain information on avoidance–preference behavior. Under uniform pH conditions, all species were found most frequently near the ends of the apparatus, particularly near the inflow. Imposition of a pH gradient altered the distribution for most species, with the region of lowest pH usually being avoided. Estimated low pH avoidance thresholds were 4.1 for yellow perch, 4.5 for white sucker, 4.7 for brook charr, 5.1 for banded killifish, 5.2 for Arctic charr, 5.4 for common shiner and blacknose dace, 5.5 for threespine stickleback, 5.7 for creek chub, and 5.9 for rainbow trout. Preferred pH ranges were usually 5–7 to 7–9. The distribution of rainbow trout in calcium gradients was not significantly different from that in uniform calcium conditions. Avoidance thresholds of the various species were generally similar to pH levels limiting natural distributions as derived from various lake and stream surveys.