Studies to prevent saprolegniasis in Atlantic salmon RAS

Authors: GOOD, CHRISTOPHER - Freshwater Institute; DAVIDSON, JOHN - Freshwater Institute; MAY, TRAVIS - Freshwater Institute; CROUSE, CURTIS - Freshwater Institute; LEPINE, CHRISTINE - Freshwater Institute; REDMAN, NATALIE - Freshwater Institute; MURRY, MEGAN - Freshwater Institute; SUMMERFELT, STEVEN - Superior Fresh; Straus, David - Dave; Harper, Susan; MARANCIK, DAVID - St George'S University; Welch, Timothy - Tim; Peterson, Brian; PEDERSEN, LARS-FLEMMING - Danish Technical University; PHUNTUMART, VIPAPORN - Bowling Green State University

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 4/1/2019
Publication Date: 5/13/2019
Citation: Good, C., Davidson, J., May, T., Crouse, C., Lepine, C., Redman, N., Murry, M., Summerfelt, S., Straus, D.L., Harper, S.B., Marancik, D., Welch, T.J., Peterson, B.C., Pedersen, L., Phuntumart, V. 2019. Studies to prevent saprolegniasis in Atlantic salmon RAS [abstract]. RAStech 2019, May 13 - 14, 2019, Washington, DC. p. 1.

Interpretive Summary:

Technical Abstract: Land-based closed containment RAS facilities, following strict biosecurity protocols, can reduce or eliminate the introduction of obligate fish pathogens. Opportunistic pathogens, however, must always be considered a risk, as these agents can cause disease during conditions that are unfavorable to fish populations. In particular, saprolegniasis (caused by Saprolegnia spp. oomycetes), is associated with enormous losses in Atlantic salmon Salmo salar aquaculture. This disease is often observed during specific stages of the salmon production cycle, namely the very early rearing fry stage, the period of smoltification, and the period immediately subsequent to vaccination. We have investigated strategies to reduce saprolegniasis during each of these high-risk production cycle stages; however, at the time of abstract submission, only one study has been completed, and the remaining two will be presented at the workshop. For our post-vaccination study, we applied daily low-dose peracetic acid (PAA) treatments while simultaneously assessing biofilter performance in replicated RAS. Twelve replicated experimental-scale RAS were stocked with Atlantic salmon parr (200 fish per RAS, 94g mean weight), after which the fish were vaccinated with a commercial salmon vaccine via intracoelomic injection. Daily static bath 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 each culture tank for a period of six weeks following vaccination. Data were collected on mortalities, Saprolegnia spp. colony counts from RAS water samples, histopathology of gill, spleen, and kidney tissues, and biofiltration as measured by total ammonia nitrogen (TAN) removal efficiency. Gross lesions and fin erosion, hemorrhage, and visible Saprolegnia spp. infection were also assessed. Unexpectedly, no major post-vaccination saprolegniasis was observed in this study; however, survival was statistically (p<0.05) lower in control parr, and clinical saprolegniasis was significantly more prevalent in the control group. PAA treatment was associated with significantly lower fish weight by study’s end. Biofilter TAN removal efficiency was not impacted by PAA administration at all dosages. PAA treatment was significantly protective against observable pectoral fin saprolegniasis and hemorrhage. Results suggest that low-dose PAA might be effective in reducing post-vaccination saprolegniasis while not significantly impacting RAS biofiltration. Further research, however, is necessary to confirm these findings, especially in commercial settings experiencing significant issues with saprolegniasis.