Rhythmicity in the emergence of Cercaria tondoni sp., a gymnocephalus cercaria from Lymnea stagnalis (Linnaeus, 1758)

Abstract

Emerging pattern of Cercaria tondoni sp., a distome (possessing a ventral sucker lying some distance from the posterior end and approximately at anterior third of the body) belonging to gymnocephalus group (having an oval body and tail devoid of stylets or spines), shows a daily rhythm, being greater during the light phase (0630:1830 h) – similar to that found in a freshwater snail Lymnea stagnalis, Linnaeus, 1758. The peak time of emergence 1230–1430 h has been measured, and there is a high risk for invertebrate or vertebrate hosts and other diurnal animals to acquire infection during this period. However 20% of total shedding in a population of cercariae has also been recorded during the dark phase (0630–1830 h) but there was no significant rhythmicity within this period. An attempt has been made to record cercarial emergence throughout the year, which is of great importance for human welfare. It was observed that the months of April, May, and June are those where frequency of emergence was highest. Implications of this rhythmicity are considered.

Keywords:

• Lymnea stagnalis
• Cercaria tondoni
• circadian rhythm
• diurnal emergence

Acknowledgements

We thank Geetanjali Mishra, Assistant Professor of Department of Zoology at University of Lucknow, Lucknow for her helpful suggestions and comments on the presented work herein. Financial assistance to S. Ray under Rajeev Gandhi National Fellowship of UGC: F-1-17.1/2011-12/ RGNF-SC-UTT-2050/(SA-III) is gratefully acknowledged.