Dynamic morphometrics of mucous cells reveal the minimal impact of therapeutic doses of peracetic acid on Atlantic salmon gill health

• Published in: Aquaculture
• Main Authors: Haddeland, Sindre, Lazado, Carlo C., Merkin, Grigory V., Myre, Ole Jacob, Okubamichael, Mearge A., Pedersen, Lars-Flemming, Pittman, Karin
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2021
• Subjects: Amoebic gill disease; Disinfection; Gill health; Mucosal immunity; Peracetic acid; Peroxide; Paa; Atlantic salmon; Salmo salar
• Online Access: https://orbit.dtu.dk/en/publications/513ae472-344d-4313-8a21-32b2883e2c8e; https://doi.org/10.1016/j.aquaculture.2020.736315; https://backend.orbit.dtu.dk/ws/files/239202436/1_s2.0_S0044848620340217_main.pdf

Mucous cells, the microscopic structural hallmark of mucosal surfaces, are highly responsive to environmental changes. Here we report how the gills of Atlantic salmon ( Salmo salar ) smolts responded to peracetic acid (PAA), a potent oxidative disinfectant and a candidate chemotherapeutant in aquaculture, through the Mucosal Mapping showing mucous cell size, volumetric density and defence activity, coupled with two-way histopathological scoring strategies. Two hundred and forty smolts were exposed to therapeutic doses of PAA on two occasions. The initial exposure included a 5-min bathing at concentrations of 0, 0.6, 1.2, and 2.4 ppm PAA. After a two-week recovery, the treatment groups were re-exposed to the same PAA concentrations for 30 min. Gill samples were collected at 2 h, 2 days, and 2 weeks after each exposure. The dynamic changes (i.e., size, volumetric density and defence activity) of the mucous cells were analysed on the distinct mucous cell populations in the gill filament and the lamella, as well as the lamellar thickness. Lamellar mucous cells were always significantly smaller (<70 μm2) and less dense (<2% volume) than those in the filament (70–100 μm 2 and 8–11% volume) giving defence activities (combination of mean mucous cell area and volumetric density in a given tissue) of 0.1–0.4 for lamellae and about 0.6–1.4 for filaments, consistent with the functions of these branchial areas. A transient sub-acute mucous cell hypertrophy was a striking response in the gill lamella to PAA during the initial and re-exposure, particularly demonstrated by the groups exposed to 0.6 and 1.2 ppm where this size change was significant. Nonetheless, the recovery was quick, suggesting more an effect of general stress than dose of PAA. Similarly, a transient reduction in hyperplasia was noted as mucous cell density decreased on the filament, but generally significant hyperplasia was not detected, and volumetric density remained unaltered regardless of treatment doses and duration of exposure. The defence ...