Wat. Res. Vol. 20, No. 7, pp. 893-897, 1986 0043-1354/86 $3.00+0.00 Printed in Great Britain Pergamon Journals Ltd EFFECTS OF METHOXYCHLOR EXPOSURE OF FLAGFISH EGGS (JORDANELLA FLORIDAE) ON HATCHABILITY, JUVENILE METHOXYCHLOR TOLERANCE AND WHOLE-BODY LEVELS OF TRYPTOPHAN, SEROTONIN AND 5-HYDROXYINDOLEACETIC ACID DOUGLAS A. HOLDWAY* and D. GEORGE DIXON Department of Biology, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada (Received August 1985) Abstract--One-day-old flagfish eggs pulse-exposed for 2 h to 0 (control), 0 (ethanol-carrier control), 1.29, 2.58, 3.51 or 5.48 mg 1 -j methoxychlor showed respective hatching successes of 92.5, 92.5, 86.3, 77.5, 72.5 and 75.0%. The methoxychlor impact was modified by the age of the eggs at exposure. Two and 3-day-eggs subjected to the same protocol showed 100% hatch for all treatments. Exposure of 1-day-old eggs also reduced the subsequent methoxychlor tolerance of the resultingjuveniles. Eight-day-oldjuveniles hatched from 1-day-oldeggs which had been exposed to 0 or 3.51 mg 1-l methoxychlor showed mean 96 h pulse-exposure methoxychlor LC~0s of 3.04 and 0.62 mgl -I respectively. Conversely, exposure of 3-day-old eggs had no impact on subsequent methoxychlor tolerance of 8-day-old juveniles; 96 h pulse-exposure LCs0 s for all treatments ranged from 2.48 to 2.55 mg 1-~. Both pre-exposure of 1-day-old eggs and pulse-exposure of 8-day-old juveniles significantly reduced whole-body tryptophan, serotonin and 5-hydroxyindoleaceticacid levels in juvenile flagfish. It was concluded that some form of protective mechanism prevented methoxychlor from affecting the embryo by 48 h post-fertilization. Up to 24 h post-fertilization, however, the embryo was detrimentally affected, as evidenced by reduced hatching success, juvenile tolerance and indoleamine levels. Key words--methoxychlor, flagfish, eggs, hatchability, toxicity, tryptophan, serotonin, 5-hydroxy- indoleacetic acid INTRODUCTION Treatment of the Athabasca and Saskatchewan Riv- ers with methoxychlor to kill larvae of the blackfly [Diptera: Simuliidae] has been undertaken in western Canada since 1974. The treatment protocol involves the introduction of a 25% emulsifiable concentrate into the rivers to create a pulse of methoxychlor (0.30 mg l-1 nominal) which moves with the current. Although nominal exposure times to the pulse range from 7.5 to 15 min, turbulent flow, adsorption and precipitation result in longer and higher exposures as the pulse moves downstream (NRC, 1983). Spawning and hatching activities of some native fish species coincide closely with larviciding (NRC, 1983), and appreciable numbers of fry have been found in drift nets downstream from the site of application of methoxychlor during field tests (Flannagan et al., 1979, 1980). Previous work has shown that a 2h pulse-exposure to methoxychlor can cause significant acute mortality in juvenile flagfish (Holdway and *Present address: Aquatic Ecology Division, National Water Research Institute, Environment Canada, Canada Centre for Inland Waters, Burlington, Ontario, L7R 4A6, Canada. Dixon, 1985), can significantly reduce brain serotonin levels in adult flagfish (Holdway et al., 1986b), and can severely impair the reproductive capacity of first generation flagfish, as well as decrease the hatch- ability and increase the incidence of deformities in their offspring when the fish are exposed once as 8-day-old juveniles and reared through 1.5 gener- ations (Holdway and Dixon, 1986). One aspect of methoxychlor larviciding which was not investigated was the effect of pulse-exposure on eggs, and on the subsequent methoxychlor tolerance of juveniles hatched from pre-exposed eggs. Since larviciding is often repeated two or more times at 2 week intervals, larval fish of species which spawned prior to the first application of methoxychlor could be exposed to a second pulse. Any effects of the first exposure (as an egg or embryo) on the subsequent methoxychlor tolerance of the resulting juveniles could be a significant factor in predicting the impacts of methoxychlor on fish populations. This study was undertaken to test the null hypoth- eses that: (1) pulse-exposure of fertilized flagfish eggs of different ages to methoxychlor has no effect on hatchability; (2) pulse-exposure of fertilized flagfish eggs of different ages to methoxychlor has no effect on the tolerance of resultant juveniles to a subsequent 893