EFFECTS OF TRICHOBILHARZIA OCELLATA ON GROWTH REPRODUCTION AND SURVIVAL OF LYMNAEA STAGNALIS

Juvenile Lymnaea stagnalis were exposed to single miracidia of Trichobilharzia ocellata after which shell lengths, numbers of eggs, and mortality of parasitized and unexposed control snails were recorded weekly. No egg-laying occurred and no significant difference in shell growth or mortality was observed during most of the prepatent period. From week 12 after exposure, infected snails laid about 1 egg/snail/week while controls laid 35-85 (mean 57) eggs/snail/week. Shell growth of infected snails continued at rates of 1.5 to 2 mm/week tapering off as maximum size was approached. Controls, on the other hand, showed a depression of growth rate to 0.5 to 1 mm/week. At 28 weeks of age all controls were dead but 90% of infected snails were alive. Histological study revealed that the ovotestis regressed and the reproductive tract failed to develop in parasitized snails but there was no evidence of mechanical damage to the gonad or digestive gland. © 1969.