Morphopathology and gill recovery of Atlantic salmon during the parasitic detachment of Margaritifera margaritifera

Abstract

During the conservation aquaculture of the freshwater mussel Margaritifera margaritifera, fish health has become a concern due to the need of mussel larvae (glochidia) to parasitize the salmonid gills and metamorphose into juveniles. However, there is a lack of information about the impact on fish during the juvenile detachment and the subsequent gill healing. To evaluate the morphopathological changes and gill recovery after the parasitism of M. margaritifera, 51 Atlantic salmon fry (Salmo salar), infested with around 22 larvae/fish g, were necropsied during the synchronized detachment of the mussel juveniles, and gills were assessed by stereomicroscopy and by light and scanning electron microscopy. Salmon showed no clinical signs during the trial and gills recovered their normal morphology almost completely in a short time, suggesting a minimal impact on fish health after glochidiosis. In this sense, the non‐erosive droplet detachment and the goblet cell hyperplasia favoured an effective gill remodelling mediated by apoptosis, polarization and cell shedding of the gill epithelia, providing insights to the defence, clearing and healing mechanisms of the gill. These morphopathological techniques could also be implemented to preserve fish welfare and to optimize the artificial breeding programmes of endangered freshwater mussels.

Epitheliocystis in Greater Amberjack: Evidence of a Novel Causative Agent, Pathology, Immune Response and Epidemiological Findings

“…Following the infection of ionocytes, in more advanced stages of the infection we observed hyperplasia of the lamellar epithelium and proliferation of epithelial cells. Proliferation of undifferentiated epithelial cells in this area is commonly reported in fish exposed to heavy metals [ 41 , 42 , 43 , 44 ], drugs [ 45 ] and organic compounds [ 46 , 47 ], as well as during different kinds of gill infections [ 48 , 49 ], where it has been correlated with the downregulation of p53 tumour suppression protein and the overexpression of proliferating cell nuclear antigen PCNA [ 50 ]. This reaction was suggested to be a fish immune strategy aiming to increase the width of the thin tissue layer that separates the shallow respiratory capillaries from the harmful agent, preventing its permeation into the blood stream [ 44 ].…”

Mucosal affairs: glycosylation and expression changes of gill goblet cells and mucins in a fish–polyopisthocotylidan interaction

“…This hyperplasia was especially notable and significant over the course of parasite exposure in the interlamellar pockets and the lamellar epithelium from 32 dpe on. A shift in the position of goblet cell distribution toward interlamellar cavities upon infection with the larval parasitic stage of the freshwater mussel Margaritifera margaritifera in Atlantic salmon was attributed to their role in gill clearance and remodeling ( 18 ). Similarly, the present rearrangement of goblet cell distribution is probably helping, by an increased mucus secretion between lamellae, to lubricate the surface of hyperplasic epithelia avoiding lamellar fusion.…”

MFLD-net: a lightweight deep learning network for fish morphometry using landmark detection

“…In aquaculture, determining the morphology is a frequent task crucial for selecting fish for culture as well as developing and testing novel fish strains. Furthermore, fish morphological traits are valuable resources for artificial breeding (Castrillo et al 2021), functional gene mapping (Figueroa et al 2018), and population-based investigations (Powers et al 2020). Morphology helps identify when fish are mature enough to produce eggs or sperm.…”