Parasitic Mites and Commensal Ciliated Protozoa in Lamellidens marginalis: Prevalence, Mean Intensity and Morphological Characteristics

The present study explores the symbiotic relationships between the common freshwater mussel Lamellidens marginalis and two associated symbionts: water mites (Unionicola spp.) and ciliates (Conchophthirus spp.). Host mussels were collected from Banipur, Habra, West Bengal, India between August 2024 and March 2025, focusing on the prevalence, anatomical localization, and morphological diversity of the symbionts. Water mites exhibited a high prevalence of 71.8%, with notable seasonal peaks in August (28.2°C) and decline in December (20°C), indicating a temperature-dependent pattern of infestation. Light microscopic analysis revealed distinct sexual dimorphism and various life stages of Unionicola, including eggs, larvae, and adults, alongside tissue nodulation and occasional pearl formation in heavily infested mussels. Conversely, Conchophthirus spp., particularly C. lamellidens and C. acuminatus, were found within gill filaments, showing moderate seasonal prevalence with a peak in January (22.5°C) and absent in the warmer months. While the adult water mites appeared to be parasitic, potentially damaging host tissues and were observed feeding on juvenile glochidium larvae of the hosts, the ciliates were largely commensal, although significant infestations could affect gill function. This research underscores the intricate dynamics of host-symbiont interactions in freshwater ecosystems and highlights the ecological significance of L. marginalis as both a host and a bioindicator, providing essential insights into aquatic health and biodiversity monitoring.