Assessing peracetic acid for controlling post-vaccination Saprolegnia spp.-associated mortality in juvenile Atlantic salmon Salmo salar in freshwater recirculation aquaculture systems

Authors: GOOD, CHRISTOPHER - Freshwater Institute; DAVIDSON, JOHN - Freshwater Institute; Straus, David - Dave; Harper, Susan; MARANCIK, DAVID - St George'S University; Welch, Timothy - Tim; Peterson, Brian; PEDERSEN, LARS-FLEMING - Technical University Of Denmark; LEPINE, CHRISTINE - Freshwater Institute; REDMAN, NATALIE - Freshwater Institute; MEINELT, THOMAS - Leibniz Institute Of Freshwater Ecology And Inland Fisheries; LIU, DIBO - Leibniz Institute Of Freshwater Ecology And Inland Fisheries; SUMMERFELT, STEVEN - Freshwater Institute

Submitted to: Aquaculture Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/5/2020
Publication Date: 2/23/2020
Citation: Good, C., Davidson, J., Straus, D.L., Harper, S.B., Marancik, D., Welch, T.J., Peterson, B.C., Pedersen, L., Lepine, C., Redman, N., Meinelt, T., Liu, D., Summerfelt, S. 2020. Assessing peracetic acid for controlling post-vaccination Saprolegnia spp.-associated mortality in juvenile Atlantic salmon Salmo salar in freshwater recirculation aquaculture systems. Aquaculture Research. 00:1-4. https://doi.org/10.1111/are.14567.
DOI: https://doi.org/10.1111/are.14567

Interpretive Summary: The disease saprolegniasis affects many species of cultured fish, particularly during periods of stress. In the Atlantic salmon industry, a particularly high-risk period is during the weeks following vaccination of juvenile fish. Because Atlantic salmon culture is increasingly being carried out in land-based systems utilizing water recirculation aquaculture system (RAS) technology, treatments for diseased fish must not only be efficacious but must not impact RAS function (i.e., biofilters must maintain nitrification while exposed to therapeutants). We sought to examine low-dose peracetic acid treatments as a means to reduce post-vaccination saprolegniasis in Atlantic salmon RAS while simultaneously assessing biofiltration function. Our major findings in this study were: i) low-dose peracetic acid significantly reduces the presence of external saprolegniasis in salmon after 6-weeks of daily post-vaccination peracetic acid treatments; ii) survival was significantly increased in fish populations exposed to daily peracetic acid treatment, relative to controls; and iii) biofiltration was not significantly impaired by daily peracetic acid treatments, at the dosages and treatment regimens tested. These results are promising with regard to the development of efficacious protocols to reduce post-vaccination saprolegniasis in Atlantic salmon RAS. Future research should expand on these findings and address the study limitations discussed in the manuscript.

Technical Abstract: Saprolegniasis is a major opportunistic disease in Atlantic salmon Salmo salar aquaculture, with critical periods of vulnerability to Saprolegnia spp. oomycetes occurring at various stages of the production cycle, especially following vaccination. With an increasing proportion of Atlantic salmon smolt production being carried out in land-based facilities utilizing water recirculation aquaculture system (RAS) technology, it is essential to develop disease control strategies that are both efficacious for fish health and not detrimental to RAS biofiltration. We sought to determine the efficacy of daily peracetic acid (PAA) water treatments (0.2 mg/L, 0.5 mg/L, and 1.0 mg/L) to reduce post-vaccination saprolegniasis while assessing biofilter performance in replicated RAS. Twelve experimental-scale RAS were stocked with Atlantic salmon parr (94g) which were subsequently vaccinated with a commercial vaccine via intracoelomic injection. During the 6-week post-vaccination period, data were collected on mortalities and clinical saprolegniasis, Saprolegnia spp. colony counts in RAS water, histopathology of gill, spleen, and kidney tissues, and biofiltration as measured by total ammonia nitrogen (TAN) removal efficiency. Gross lesions and fin damage / hemorrhage were noted at study’s end. Ultimately, no major post-vaccination Saprolegnia spp.-associated mortality was observed; however, survival was statistically (p<0.05) lower in control parr, and clinical saprolegniasis was significantly more prevalent in the control group. Conversely, PAA treatment was associated with significantly lower fish weight. Biofilter TAN removal efficiency was not impacted by PAA administration at all dosages. Water sample plate counts of Saprolegnia spp. colonies increased over time in all treatment groups during the post-vaccination period. Treatment with PAA was significantly protective against pectoral fin saprolegniasis and hemorrhage; however, fin damage in general was not associated with PAA treatment. No treatment-associated lesions were noted during histopathology assessments. Results suggest that PAA can be effective in reducing post-vaccination saprolegniasis in Atlantic salmon while not significantly impacting biofiltration.