A Chemical Selectively Lethal to Squawfish (Ptychocheilus oregonensis and P. umpquae)

Abstract

A piscicide, 1,1′-methylenedi-2-naphthol, is lethal to Ptychocheilus oregonensis and P. umpqua at concentrations 3 to 100 times more toxic to squawfish than to salmonids. Selectivity of the chemical varies with the tolerances of the species and its potency varies positively with concentration and temperature. For a thermal range of 18.3 to 10.0 C, the minimum LC100 is 0.006 to 0.015 ppm for P. oregonensis and 0.01 to 0.03 ppm for P. umpquae. Within these ranges the mean survival time varies from 6 to 31 hr for P. oregonensis and 6 to 20 hr for P. umpquae. In 96-hour assays at similar temperatures, the maximum LC0 is about 0.3 ppm for Salvelinus fontinalis, 0.1 ppm for Oncorhynchus tshawytscha, and from 0.6 to 1.3 ppm for O. kisutch and Salmo gairdneri depending on the water temperature. One domestic sheep and two ducks showed no ill effects when forced to drink water containing 10 ppm of the chemical for 1 week. A field application in a small lagoon containing several species of fish killed only P. oregonensis.