Effect of a prophylactic treatment with chloramine-T on gill histology and microbiome of Atlantic salmon ( Salmo salar ) under commercial conditions

• Published in: Aquaculture
• Main Authors: Quezada-Rodriguez, PR, Taylor, RS, Samsing, F, Rigby, M, Wood, AT, Nowak, BF, Wynne, JW
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier Science Bv 2022
• Subjects: Agricultural; Veterinary and Food Sciences; Fisheries sciences; Aquaculture; Atlantic salmon; Salmo salar
• Online Access: https://doi.org/10.1016/j.aquaculture.2021.737319; http://ecite.utas.edu.au/146939

Chloramine-T (Cl-T) is a disinfectant and sanitizer widely applied to treat bacterial infections on the gill and skin of Atlantic salmon during freshwater culture. It is typically applied as static or flush treatments during periods of disease risk or in response to pathogen detection or gross disease signs. While the efficacy of CI-T to reduce specific bacterial pathogens has been demonstrated previously, its effect on the broader commensal microbial community is largely unknown. To address this knowledge gap, the present study examined the effects of a one-hour Cl-T treatment (nominal 15mgL −1 ) on the skin and gill microbiome using a 16S rRNA based amplicon sequencing approach. Furthermore, the total bacterial load and histological changes in the gill were examined following CI-T treatment. Although, bacterial quantification on gills and water confirmed decreased bacterial load at 1h, these loads returned to pre-treatment levels by 24h. Microbial richness of bacterial communities on skin and gills varied at 1h, and 13d compared to 0h. Contrary to the gills, microbial diversity on skin decreased after treatment. Gill histology showed subepithelial oedema at 24h and increased number of lamellar mucous cells at 7d compared with 0h. This study reports the effects of commercially deployed Cl-T on two gill health indicators: bacterial microbiome composition and gill morphology in fresh water farmed Atlantic salmon.