Pulse versus continuous peracetic acid applications: effects on Rainbow trout performance, biofilm formation and water quality

Authors: LIU, DIBO - Leibniz Institute Of Freshwater Ecology And Inland Fisheries; Straus, David - Dave; PEDERSEN, LARS-FLEMMING - Technical University Of Denmark; MEINELT, THOMAS - Leibniz Institute Of Freshwater Ecology And Inland Fisheries

Submitted to: Aquacultural Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/15/2017
Publication Date: 5/1/2017
Citation: Liu, D., Straus, D.L., Pedersen, L., Meinelt, T. 2017. Pulse versus continuous peracetic acid applications: effects on Rainbow trout performance, biofilm formation and water quality. Aquacultural Engineering. 77:72-79.

Interpretive Summary: Peracetic acid (PAA) products are commercial mixtures of acetic acid and hydrogen peroxide brewed under pressure to make a potent disinfectant and are currently being introduced to aquaculture as sustainable disinfectants. We wanted to see if a short term high dose (1 - 2 ppm PAA) applications or continuous low dose (< 0.2 ppm PAA) applications were better to use with rainbow trout. The twice-per-week short-term applications of 1 mg L-1 PAA caused stress in fish from the initial application, but they quickly adapted to this, while the continuous application of 0.2 mg L-1 PAA caused no stress. There was no difference between treatments in growth or immune function. Therefore, the high-dose pulse PAA application has certain advantages over continuous low-dose PAA application, such as ease of handling and better water quality.

Technical Abstract: Peracetic acid (PAA) products are being introduced to aquaculture as sustainable disinfectants. Two strategies are used to apply PAA: short term high dose (1-2 mg L-1 PAA) periodic pulse applications or continuous low dose (< 0.2 mg L-1 PAA) applications. In the present study, these strategies and an unexposed control group were compared in nine identical flow-through tanks stocked with rainbow trout (Oncorhynchus mykiss) at similar densities and constant water exchange rates. The twice-per-week pulse applications of 1 mg L-1 PAA induced stress in fish from the initial application, while the continuous application of 0.2 mg L-1 PAA caused no stress to fish. Fish progressively adapted to the pulse applications by regulating the cortisol release to the unstressed level. Meanwhile, neither growth nor innate cellular immunity was affected. A high PAA concentration persisted during the pulse applications with a slower decay, resulting in an antimicrobial effect which nearly inhibited biofilm formation, but partially inhibited nitrification. Consequently, the highest oxygen concentration was measured and no long-term pH changes were observed. In contrast, PAA showed rapid decay during continuous applications, resulting in undetectable trace concentrations of PAA and H2O2. The continuous application of PAA promoted visible biofilm formation through the continuous input of organic carbon (acetic acid). Meanwhile, trace amounts of PAA, as exogenous reactive oxygen species, likely induced a mild oxidative stress to microbes. Compared to algae in the biofilm, bacteria are more vulnerable to oxidative stress. Consequently, the composition of the biofilm was likely dominated by algae, resulting in a long-term pH increase and a higher oxygen concentration. Based on these results, high-dose pulse PAA application has certain advantages over continuous low-dose PAA application, such as ease of handling, and a more pronounced antimicrobial effect which results in better water quality. The continuous low-dose application of PAA to tanks enhanced biofilm, which could provide a potential protective habitat for opportunistic fish pathogens.