Acute Toxicity of Methoxychlor to Larval White Sucker (Catostomus commersoni) as Modified by Age, Food Availability, and Egg Preexposure

Abstract

Methoxychlor is currently pulsed into several western Canadian rivers at 0.30 mg∙L−1 to control the emergence of blackflies (Diptera: Simuliidae). A 2-h exposure of white sucker (Catostomus commersoni)) eggs to 4.83 mg methoxychlor∙L−1 at 1, 3, or 6 d postfertilization increased the incidence of deformities in both 1-d-old and pooled 3- and 6-d-old eggs (2.9 and 3.1%, respectively) compared with control eggs(1.1%). Larvae from exposed eggs showed a 2-d delay in the onset of exogenous feeding. Exposure as eggs increased methoxychlor tolerance. Respective 168-h PE LC50s (the 2-h pulse-exposure concentration causing 50% mortality over 168 h) for 2-d-old larvae from control eggs and eggs exposed for 2 h to methoxychlor at 1, 3, or 6 d postfertilization were 0.36, 1.04, 2.05, and 2.67 mg∙L−1 Methoxychlor toxicity in control larvae was modified by age; 10-d-old larvae were less tolerant than 2-, 18-, and 26-d-old larve, with respective PE LC50s of 0.04, 0.36, 0.34, and 0.20 mg∙L−1. After the onset of feeding, food availability modified toxicity. The96-h PE LC50sfor 18-d-oldfedand unfed larvae and 26-d-old fed and unfed larvae were 0.34, 0.032, 0.20, and 0.038 mg∙L−1, respectively. Swimbladder development was arrested in 2-d-old larvae exposed for 2 h to 0.10 mg methoxychlor∙L−1 at 9 d of age. White sucker survival may be at risk in methoxychlor-treated rivers.