THE DEVELOPMENT OF TISSUE LESIONS IN THE SNAIL LYMNAEA-GLABRA EXPOSEDTO A SUBLETHAL DOSE OF MOLLUSCICIDE

Histological examinations were undertaken in adult Lymnaea glabra to d etermine whether tissue lesions develop in snails that survived exposu re to a molluscicidal agent and thus impair survival or reproduction c apacities of remaining snails. The snails were exposed for 4 days to s ublethal doses of niclosamide (0.21 mg/L), 3,4-dichloro-2-benzamido-5- nitrolhiazole (0.13 mg/L), or 3,5-dichloro-2-benzamido-5-nitrothiazole (0.15 mg/L) at 20 degrees C. After exposure, the surviving snails wer e maintained under normal conditions (oxygenated water) for a further 21 days. The niclosamide group revealed epithelial necrosis in the dig estive glands and the gonads. This was followed by reconstitution from day 12 or 19. The same sequence of tissue lesions also occurred in th e kidney, however, a second phase of epithelial necrosis developed in the reconstituted epithelium after day 19. In the two other groups, ti ssue lesions of the three viscera developed in very similar manner, re gardless of the molluscicide chosen for these experiments. Although th e molluscicidal doses were sublethal in these snails, 12-19 days at 20 degrees C were required to reconstitute the visceral epithelium. Snai ls that survived the molluscicidal agent were thus impaired for one we ek or more in normal conditions.