Abstract
Fish gills are heavily exposed to the external milieu and may react against irritants with different cellular responses. We describe variations in mucous cell counts in gills from healthy Atlantic salmon (Salmo salar) presmolts in five recirculating aquaculture system (RAS) farms and one flow-through farm. Based on certain criteria, mucous cells were histologically quantified in a defined lamellar region of the gills and the counts were analysed. Immunohistochemistry (IHC) was used to investigate epithelial responses. The median number of total mucous cells in the defined region was 59 per fish. Between the farms, the medians varied from 31 to 101 with the lowest in the flow-through farm. A regression model was fitted with "total mucous cells" as the dependent variable and with "fish length" and "fish farm" as independent variables. The proportion of variation in mucous cell counts explained by the model was twice as high when "fish farm" was included compared to only "fish length." IHC revealed proliferative responses in coherence with high mucous cell numbers. Conclusively, the variation in mucous cell counts depends on combined farm-related factors. Establishing a baseline for mucous cell counts is fundamental in the development of high-throughput monitoring programmes of gill health in farmed fish.
Highlights
Salmon (Salmo salar) smolt have been reared in landbased facilities using water from nearby rivers or lakes which flow through the production site
This is the first study describing the variation in mucous cell count from gills of clinically healthy salmon reared in commercial fish farms in Norway
We have developed a method of counting mucous cells from salmon gill histology samples
Summary
Salmon (Salmo salar) smolt have been reared in landbased facilities using water from nearby rivers or lakes which flow through the production site. A baseline for mucous cell counts is fundamental in the development of a future high-throughput monitoring programme of gill health in farmed fish This would be of special interest in RAS facilities, where gill health has been pinpointed as one of the critical concerns (Becke, Schumann, Steinhagen, Geist, & Brinker, 2018; Dahle et al, 2020; Hjeltnes et al, 2012). In this cross-sectional study, the overall aim was to investigate the prevalence of mucous cells in presmolts from five different RAS facilities and one FT farm. This was approached through two objectives: first, to implement a counting method of mucous cells in salmon gills, and second, to describe the variations in mucous cell count in salmon and between different salmon production sites
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
