The development of tissue lesions in the snail Lymnaea glabra exposed to a sublethal dose of molluscicide.

Histological examinations were undertaken in adult Lymnaea glabra to determine whether tissue lesions develop in snails that survived exposure to a molluscicidal agent and thus impair survival or reproduction capacities of remaining snails. The snails were exposed for 4 days to sublethal doses of niclosamide (0.21 mg/L), 3,4-dichloro-2-benzamido-5-nitrothiazole (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 were maintained under normal conditions (oxygenated water) for a further 21 days. The niclosamide group revealed epithelial necrosis in the digestive glands and the gonads. This was followed by reconstitution from day 12 or 19. The same sequence of tissue lesions also occurred in the kidney, however, a second phase of epithelial necrosis developed in the reconstituted epithelium after day 19. In the two other groups, tissue lesions of the three viscera developed in very similar manner, regardless of the molluscicide chosen for these experiments. Although the molluscicidal doses were sublethal in these snails, 12-19 days at 20 degrees C were required to reconstitute the visceral epithelium. Snails that survived the molluscicidal agent were thus impaired for one week or more in normal conditions.