Disruption of swimming in the hyperbenthic mysid Neomysis integer (Peracarida : Mysidacea) by the organophosphate pesticide chlorpyrifos

Mysids are used routinely by regulatory authorities for conducting 96 h LC5 0 toxicity tests to evaluate the potential hazards of pollutants to aquatic ecosystems. Data from these acute tests suggest that the European estuarin e mysid Neomysis integer (Peracarida: Mysidacea) is comparatively sensitive to trace metals and organophosphate pesticides, and may be a suitable alte rnative to the frequently-used sub-tropical American mysid Americamysis (= Mysidopsis) bahia for testing the toxicity of chemical contaminants to Euro pean estuarine biota. There is, however, growing demand for the development of toxicity tests which are more representative of the effects of toxic co ntaminants on natural populations, and which provide results that are more readily extrapolated to natural ecosystems, than acute tests. Behavioural d isruption, particularly of swimming ability, is used increasingly in labora tory toxicity studies as a sensitive endpoint for assessing the effects of contaminants on aquatic biota. This paper describes a sensitive laboratory technique, using an annular flume, to determine the effects of an organopho sphate pesticide on the swimming behaviour of N. integer. Following 7-day e xposure to 0.038 mu g chlorpyrifos l(-1), mysids became hyperactive and mor e swam forward into a slow current (3 cm s(-1)) than control mysids. Despit e this hyperactivity, pesticide-exposed mysids were unable to swim faster t han 15 cm s(-1), whereas control mysids were able to swim faster than 18 cm s(-1). Other changes in swimming behaviour following pesticide exposure in cluded fewer mysids maintaining position, and more mysids swimming with the current at high current velocities (18 cm s(-1)), than control individuals . These responses of chlorpyrifos-exposed N. integer are predicted to cause reduced ability of N. integer to maintain position in the natural estuarin e habitat. Furthermore, the swimming behaviour of N. integer was affected a t pesticide concentrations below the 7 day LC50 (0.084 mu g chlorpyrifos l( -1)), highlighting the importance of using sub-lethal toxicity studies for predicting environmental consequences of pollutant discharge. (C) 1999 Else vier Science B.V. All rights reserved.