Investigating the effectiveness of peracetic acid to reduce post-vaccination Saprolegnia spp.-associated mortality in Atlantic salmon parr while assessing impact on nitrification in recirculation aquaculture systems

Authors: GOOD, CHRIS - Freshwater Institute; DAVIDSON, JOHN - Freshwater Institute; Straus, David - Dave; Harper, Susan; MARANCIK, DAVE - St George'S University; Welch, Timothy - Tim; LEPINE, CHRISTINE - Freshwater Institute; Wolters, William; Peterson, Brian; PEDERSEN, LARS-FLEMING - Danish Technical University; PHUNTUMART, VIPA - Bowling Green State University; SUMMERFELT, STEVE - Freshwater Institute

Submitted to: Aquaculture Europe 2016 - Book of Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 7/4/2016
Publication Date: 9/21/2016
Citation: Good, C., Davidson, J., Straus, D.L., Harper, S.B., Marancik, D., Welch, T.J., Lepine, C., Wolters, W.R., Peterson, B.C., Pedersen, L., Phuntumart, V., Summerfelt, S. 2016. Investigating the effectiveness of peracetic acid to reduce post-vaccination Saprolegnia spp.-associated mortality in Atlantic salmon parr while assessing impact on nitrification in recirculation aquaculture systems [abstract]. Aquaculture Europe 2016 - Book of Abstracts, Edinburgh, September 20-23, 2016, Scotland. p. 397-398.

Interpretive Summary:

Technical Abstract: Closed containment operations utilizing recirculation aquaculture systems (RAS) can provide critical barriers to the introduction of obligate fish pathogens (Timmons and Ebeling, 2010); however, opportunistic pathogens will be present and can cause disease when conditions favor these agents. One particular opportunistic disease, saprolegniasis (caused by Saprolegnia spp. oomycetes), is associated with enormous losses in the aquaculture industry (Van West, 2006). It is estimated that 10% of all hatched farmed Atlantic salmon Salmo salar die from saprolegniasis (Bruno et al., 2011). A major risk period for saprolegniasis is during the weeks following vaccination. Given that Atlantic salmon smolt production is increasingly being carried out in RAS, therapeutic strategies must also consider potential impacts on biofiltration. We sought to investigate daily peracetic acid (PAA) treatment dosages to determine their effectiveness in reducing post-vaccination losses to Saprolegnia spp. infections while assessing biofilter performance in replicated RAS. Materials and methods Twelve replicated experimental-scale RAS with fluidized sand biofilters were stocked with Atlantic salmon parr (approximately 200 fish per RAS, 94g mean weight); fish were subsequently vaccinated with a commercial salmon vaccine via intracoelomic injection. Daily pulse treatments with PAA – i) 0.2 mg/L, ii) 0.5 mg/L, iii) 1.0 mg/L, or iv) deionized water (control) – were administered to culture tank water for six weeks post-vaccination. During this period, the following data were collected, either daily or at regular intervals: mortalities and incidence of clinical saprolegniasis; Saprolegnia spp. colony counts from RAS water samples; gill, spleen, and kidney histopathology; and biofilter functionality, as measured by total ammonia nitrogen (TAN) removal efficiency. An end-of-study welfare assessment was also conducted, examining fish for gross lesions and fin erosion, hemorrhage, and visible Saprolegnia spp. infection. Results No major post-vaccination Saprolegnia spp.-associated mortality was observed in this study. Survival was statistically (p<0.05) lower in control parr, and clinical saprolegniasis was significantly more prevalent in the control group. There was an apparent protective effect, however PAA treatment was also associated with lower fish weight by study’s end. Biofilter TAN removal efficiency was not impacted by PAA administration at all dosages (Fig. 1). Water counts of Saprolegnia spp. increased over time in all treatment groups during the post-vaccination period. At study’s end, welfare assessments indicated that PAA treatment was significantly protective against observable pectoral fin saprolegniasis and hemorrhage; however, fin erosion in general was not associated with PAA treatment. At the time of abstract submission, histopathology data are still forthcoming, and will be presented at Aquaculture Europe 2016. Overall, results thus far indicate that daily low-dose PAA application can be effective in reducing post-vaccination saprolegniasis in Atlantic salmon while not significantly impacting RAS biofiltration; however, further research is necessary to refine PAA dosage and to assess its effectiveness in controlling saprolegniasis in commercial settings. References Bruno D.W., P. Van West, and G.W. Beakes. 2011. Saprolegnia and other oomycetes. In: Fish Diseases and Disorders: Volume 3: Viral, Bacterial and Fungal Infections. p. 669-720. Woo, P.T.K. and D.W. Bruno (Eds). CABI International, Wallingford. 930p. Timmons, M.B. and J.M. Ebeling. 2010. Economic Realities and Management Issues. p.707-742. In: Recirculating Aquaculture. Cayuga Aqua Ventures, Ithaca. 975p. Van West, P. 2006. Saprolegnia parasitica, an oomycete pathogen with a fishy appetite: new challenges for an old problem. Mycologist 20: 99–104.