Reducing mortality associated with opportunistic infections in Atlantic salmon Salmo salar fry using hydrogen peroxide and peracetic acid

Authors: DICOCCO, ANNA - Freshwater Institute; MAY, TRAVIS - Freshwater Institute; CROUSE, CURTIS - Freshwater Institute; MARANCIK, DAVID - St George'S University; PHUNTUMART, VIPAPORN - Bowling Green State University; GHOSH, SATYAKI - Bowling Green State University; BELIGALA, GAYATHRI - Bowling Green State University; REDMAN, NATALIE - Freshwater Institute; MURRAY, MEGAN - Freshwater Institute; FISCHER, GREGORY - University Wisconsin-Stevens Point-northern Aquaculture Demonstration Facility; SUMMERFELT, STEVEN - Freshwater Institute; GOOD, CHRISTOPHER - Freshwater Institute

Submitted to: Aquaculture Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/23/2021
Publication Date: 2/17/2021
Citation: Dicocco, A., May, T., Crouse, C., Marancik, D., Phuntumart, V., Ghosh, S., Beligala, G.U., Redman, N., Murray, M., Fischer, G., Summerfelt, S., Good, C. 2021. Reducing mortality associated with opportunistic infections in Atlantic salmon Salmo salar fry using hydrogen peroxide and peracetic acid. Aquaculture Research. 52(7):3101-3109. https://doi.org/10.1111/are.15155.
DOI: https://doi.org/10.1111/are.15155

Interpretive Summary: Cultured Atlantic salmon can be highly susceptible to opportunistic infections during early life-stages, especially when exposed to additional physical and environmental stressors. As such, developing efficacious protocols for applying water disinfectants to prevent or reduce mortalities during the fry stage would be beneficial for Atlantic salmon producers. This study assessed the use of hydrogen peroxide and peracetic acid as disinfectants to reduce mortality associated with the opportunistic pathogen Saprolegnia, and the effects of these disinfectants on water quality. Tanks of Atlantic salmon treated with hydrogen peroxide, but not peracetic acid, exhibited better survival compared to tanks that were not treated with a disinfectant. Most water quality parameters measured in this study were not affected by these disinfectants. These results suggest that, at the dosage and treatment regimens tested, hydrogen peroxide can be a safe and efficacious water treatment for reducing Atlantic salmon fry mortality during periods of stress.

Technical Abstract: Cultured Atlantic salmon Salmo salar can be highly susceptible to opportunistic infections during early life-stages, especially when exposed to additional physical and/or environmental stressors. As such, developing efficacious protocols for applying water disinfectants to prevent or reduce mortalities during the fry stage would be beneficial for Atlantic salmon producers. To this end, we exposed Atlantic salmon fry (0.47 g ± 0.02) to daily handling stress and 120% over-feeding over a 4-week period while simultaneously providing daily 30-min static bath treatments of (i) 15 mg/L hydrogen peroxide (H2O2), (ii) 0.2 mg/L peracetic acid (PAA), or (iii) 0.5 mg/L PAA. Mortality was assessed daily over the study period, and skin and gill samples were collected at 2- and 4-weeks for histopathology to evaluate tissue health in response to treatment exposure. Moribund fish were also regularly assessed via wet-mount microscopy, with organisms resembling Saprolegnia spp. routinely observed on the gills of affected fish. Tanks treated with H2O2 had significantly (p<0.05) higher survival (83.7% ± 1.7) compared to controls (69.5% ± 5.2) while no significant differences were observed between either PAA treatments (76.6% ± 0.6 and 77.4% ± 3.0 survival in the 0.2 mg/L and 0.5 mg/L PAA groups, respectively) and controls. Interestingly, no significant differences were noted among treatments for waterborne Saprolegnia spp. concentrations, through quantification of Saprolegnia spp. genomic DNA through qPCR. Lower total suspended solids (TSS) were observed in both PAA treatment groups; all other measured water quality parameters were not significantly different among treatments. No treatment impacts were noted through histopathology at either sampling point. These results suggest that, at the dosage and treatment regime tested, H2O2 can be a safe and efficacious water treatment for reducing Atlantic salmon fry mortality associated with opportunistic infections during periods of physical and environmental stress. Assessments of alternative PAA treatment regimens should also be considered in future research aimed at reducing early life-stage mortality in Atlantic salmon.