Early stages of Margaritifera margaritifera glochidiosis in Atlantic salmon: Morphopathological characterization

• Published in: Journal of fish diseases 2020-01, Vol.43 (1), p.69-80
• Main Authors: Castrillo, Pedro A., Varela‐Dopico, Catuxa, Ondina, Paz, Quiroga, María Isabel, Bermúdez, Roberto
• Format: Article
• Language: English
• Subjects: Animals; Bivalvia - growth & development; Bivalvia - physiology; Body organs; Critically endangered species; Degeneration; Endangered species; Epithelium; Fish; Fish Diseases - parasitology; Fish Diseases - pathology; Freshwater; Freshwater fishes; Freshwater molluscs; freshwater pearl mussel; gill histopathology; Gills; Gills - parasitology; Glochidia; glochidium; Host-parasite interactions; Individual rearing; Inflammation; Inland water environment; Larvae; Lesions; Life cycle; Life cycles; Light microscopy; Margaritifera margaritifera; Marine fishes; Mollusks; Mucosa; Mussels; Optical microscopy; Organs; parasite; Parasites; Parasitic diseases; Parasitoses; Pathogenesis; Rare species; Salmo salar; Salmo salar L; Salmon; Stereomicroscopy; Survival; Threatened species; Wildlife conservation
• ISSN: 0140-7775; 1365-2761
• DOI: 10.1111/jfd.13100

Freshwater mussels of the order Unionida encyst into the fish mucosa to metamorphose and complete their life cycle, causing a parasitic disease known as glochidiosis. This parasitic stage represents a bottleneck for the survival of naiads, particularly for critically endangered species as Margaritifera margaritifera; however, little is known about the events occurring during this critical stage. Therefore, this study aimed to histologically characterize the development of M. margaritifera glochidiosis in Atlantic salmon to get insight into the pathogenesis of this interaction. Fish exposed to glochidia were sampled during the first 44 days post‐exposure, and organs were observed by stereomicroscopy and light microscopy. Glochidia attached to the gills by pinching the lamellar epithelium, whereupon an acute proliferative branchitis engulfed most of the larvae. However, during the first 14 days, a severe detachment of unviable glochidia occurred, associated with the presence of pleomorphic inflammatory infiltrate and epithelial degeneration. In the cases where larvae remained attached, a chronification of the lesions with none to scarce inflammation was observed. These results provide key information to better understand the complex host–parasite interaction during the early stages of glochidiosis and provide valuable information to optimize artificial rearing of naiads in conservation of threatened freshwater mussel populations.