LETHAL AND SUBLETHAL EFFECTS OF MALATHION ON 3 LIFE STAGES OF THE GRASS SHRIMP, PALAEMONETES-PUGIO

The effects of malathion exposure on three life stages of the grass sh rimp (Palaemonetes pugio) were evaluated. After 96-h exposures, malath ion was most toxic to newly hatched larvae with an LC50 of 9.06 mu g l (-1) followed by an LC50 of 13.24 mu g l(-1) for 18-day-old larvae and an LC50 of 38.19 mu g l(-1) for adult shrimp. In a separate bioassay, to simulate field conditions, newly hatched larvae were exposed to ma lathion at 6 h day(-1) every 5 days al a salinity of 10 parts per thou sand? until metamorphosis to postlarvae. After four pulse dose exposur es, mortality was highest in the two highest concentrations, of 15.0 a nd 30.0 mu g l(-1). The number of instars to postlarvae was significan tly lower in the highest concentration compared to control. The findin gs indicate that malathion may not directly affect growth in a measura ble way but may alter natural metamorphic rhythms at the highest conce ntrations. Whole body acetylcholinesterase (AChE) activity was measure d on Day 0 and Day 15 from the pulse exposure lest. AChE activities we re not significantly different from controls. Other factors than just AChE inhibition may have contributed to malathion toxicity. (C) 1998 P ublished by Elsevier Science B.V. All rights reserved.