Effect of chronic exposure to EPN and to Guthion on the critical swimming speed and brain acetylcholinesterase activity of Cyprinodon variegatus

Swimming performance of the estuarine sheepshead minnow, Cyprinodon variegatus, was measured in a stamina tunnel at the end of life-cycle toxicity tests with the organophosphate pesticides EPN (265 days) and Guthion (219 days). Effects of acetylcholinesterase (AChE) inhibition were also determined. These measures were compared to survival, growth and reproduction data obtained in the life-cycle toxicity test. Significant effects on swimming stamina were detected in fish exposed to 2.2 μg EPN/1 (57% that of control fish) and in fish exposed to 4.1 μgEPN/1 (46% of controls). Survival and growth were reduced only in 7.9 μg EPN/1. Swimming performance was not affected by Guthion concentrations up to 0.5 μg/1, a concentration affecting reproduction. AChE was significantly inhibited by all tested concentrations of EPN, 0.25 to 7.9 μg/1, and Guthion, 0.06 to 0.50 μg/1. Swimming stamina may be an important endpoint to include with measurements of effects on survival, growth and reproduction in chronic toxicity tests with fish, but the relation of AChE inhibition to these endpoints is uncertain.