The Toxicity of Organic Phosphorus Insecticides to Different Species of Warmwater Fishes

Abstract

Bioassays were conducted with thirteen organic phosphorus insecticides to determine their relative toxicity to four species of fish. An extremely wide range in toxicity was found with 96-hour TLm (median tolerance limit) values ranging from 0.0052 to 610 p.p.m. Bluegills were generally the most sensitive fish, followed by guppies, fathead minnows, and then goldfish. The maximum sensitivity of the different species to particular compounds ranged from 4 to as high as 900 times the minimum. Additional experiments were conducted with some of the compounds. Larger bluegills (10 grams) were slightly more tolerant than smaller bluegills (2 grams) to Delnav, parathion, and malathion; green sunfish of similar size and largemouth bass (5 grams) were not greatly different in sensitivity from the larger bluegills. Tests of five compounds revealed that the toxicity of emulsible concentrates or wettable powders was similar to that of the technical grade material. Fathead minnow fry from 2 to 30 days old were about ten times as sensitive to Delnav as adults. However, when exposed to TEPP there was little difference in sensitivity between the fry and adults. During exposure for 15 days the toxic effect of Delnav increased about fivefold over that shown in 96 hours, but there was no additional fish mortality between 15 and 30 days.