PW09 Pesticide I
8:00 AM - Wednesday
(PW159) Stage-specific toxicity of medaka (Oryzias latipes) eggs and embryos to cypermethrin using a refined methodology for an in vitro fertilization bioassay.
Gonzalez-Doncel, M.1, 2, Fernandez-Torija, C.1, Hinton, D.E.2, Tarazona, J.V.1, 1 INIA, Madrid, Madrid, Spain2 Duke University, Durham, NC, U.S.A.
ABSTRACT- Using original artificial fertilization methods with medaka (Oryzias latipes), the effects of exposure to cypermethrin on gametes, fertilization, and embryonic development were investigated. The relative sensitivity was studied when brief exposures to six nominal concentrations of cypermethrin ranging from 3.13 
g/L to 100 g/L were initiated at different developmental stages: i.e. unfertilized egg (stage 0), late morula (stage 9), eminence of swim bladder (stage 29), and maximum flexion of the atrio-ventricular region (stage 34). Cypermethrin did not affect the fertilization process. Predominant sublethal effects in embryos included transient visceral edemas intimately associated to the gall bladder, with subsequent pericardial edemas. Parallel studies on heart rate could not conclude any relationship with pericardial edemas. Other sublethal effects were observed in surviving larvae and included: spastic movements with or without ability to respond to stimulus (≥ 6.25 g/L); spinal curvatures; and, delayed or absence of swim bladder inflation (≥ 12.5 g/L). The exposure of the gametes (stage 0) or during the earlier embryonic development (stages 9 or 29) was not a critical window for cypermethrin exposure. Although incidence of edemas in embryos occurred mainly during these early exposures, embryo and larva lethality, and incidence of transient sublethal effects in hatchlings proved the later exposure window (stage 34) the most sensitive. Our study reinforces the idea that a combination of morphological and functional impairment evaluation is a more subtle response to developmental toxicants than mortality or morphological defects alone. This work was partially supported by the Spanish Grant No. REN2003-06917-C02-01.
Key words: gametes, Medaka, fertilization, developmental toxicity