SWIMMING PERFORMANCE AND PREDATOR AVOIDANCE BY MUMMICHOG (FUNDULUS-HETEROCLITUS) LARVAE AFTER EMBRYONIC OR LARVAL EXPOSURE TO METHYLMERCURY

Embryos of the mummichog, Fundulus heteroclitus, were exposed to 5 and 10 mu g/L methylmercury throughout development; these are concentrati ons below those that cause teratological effects. Larvae were maintain ed in clean seawater or in water with methylmercury, and tested for sw imming performance by chasing them with a glass rod. Swimming performa nce improved with larval age. Larvae that had been exposed to methylme rcury as embryos swam greater distances than controls, while those tha t were exposed only as larvae swam less than controls. The effects of the embryonic exposure diminished over time, and the larval environmen tal conditions took precedence. Larvae were also tested with two preda tors, the grass shrimp, Palaemonetes pugio, and 1-year-old mummichogs. Those that had been exposed to mercury as embryos (which swam more th an controls) or as larvae (which swam less than controls) were more su sceptible to predation than controls. The increased swimming of those exposed as embryos may have reflected greater activity, making them mo re likely to attract the predator's attention, while the slower swimmi ng of those exposed as larvae could make them easier to capture.