Effects of repeated exposure to peracetic acid (PAA) in Atlantic salmon smolts
Amoebic gill disease (AGD) is a serious threat in Atlantic salmon (Salmo salar) aquaculture. Current strategies including freshwater and hydrogen peroxide treatments have limitations and ecological concerns. Therefore, sustainable alternatives must be explored. Peracetic acid is currently being explored as an alternative treatment for amoebic gill disease AGD (FHF project nr 901472). Before its actual application to AGD-infected fish, its health-related consequences in naive salmon need to be documented. We have conducted two exposure trials in 2018 at DTU Aqua (Hirtshals, Denmark) and preliminary results indicate that salmon physiology can cope up with PAA (doses from 0 to 4,8 ppm), with no records of mortality. In the present trial, we aim to explore the impacts of repeated exposure to 10 ppm PAA with varying exposure durations on the health and welfare of salmon. This concentration has been shown to significantly reduce N. perurans viability in vitro. Repeated exposure will have industrial applications since AGD treatment is conducted several times during a production cycle. This study is expected to further build the credential of PAA as a chemotherapeutant with potent anti-parasitic activity but with minimal disturbances in salmon physiology. As an oxidant, PAA may induce oxidative stress in salmon. But we hypothesise that salmon can physiologically cope up with the pressure of PAA in the environment.
There will be 2 sub-experiments involved in the trial described in this application: Sub-experiment 1: A trial aimed at documenting the behavioral, morphological and physiological changes in salmon following a 15 min or 30 min-long PAA exposure, which will be performed every 3 weeks; and Sub-experiment 2: A trial where the PAA-exposed fish will be subjected to an acute stress challenge.
In Sub-experiment 1, there will be 3 treatment groups – 0 ppm, 10 ppm for 15 mins and 10 ppm for 30 min. Each group will have 120 fish distributed into 3 replicate tanks (total number of fish: 360). The experimental fish will be exposed to PAA treatment every three weeks and there will be 3 exposures in total. Fish (3 per tank) will be sampled before and 24 h after each exposure.
In Sub-experiment 2, the remaining fish after the repeated exposure experiment will be subjected to an acute stress challenge through increased density for 1 hr. Thereafter, physiological responses to stress will be evaluated at 2, 6, 24 and 48 hr after the challenge by collecting plasma and tissue samples.
We are establishing the credential of PAA as a potential treatment for AGD in salmon, which excludes any possibility for replacement of experimental animals. However, we have merged several questions and hypotheses into one experiment divided into two interconnected sub-trials. The number of fish included in this study has been kept to a minimun (total 360) that is expected to provide robust and statistically relevant analyses. The experiment uses only small tank units (900-L). This will reduce the number of fish needed for the experiment.
There will be 2 sub-experiments involved in the trial described in this application: Sub-experiment 1: A trial aimed at documenting the behavioral, morphological and physiological changes in salmon following a 15 min or 30 min-long PAA exposure, which will be performed every 3 weeks; and Sub-experiment 2: A trial where the PAA-exposed fish will be subjected to an acute stress challenge.
In Sub-experiment 1, there will be 3 treatment groups – 0 ppm, 10 ppm for 15 mins and 10 ppm for 30 min. Each group will have 120 fish distributed into 3 replicate tanks (total number of fish: 360). The experimental fish will be exposed to PAA treatment every three weeks and there will be 3 exposures in total. Fish (3 per tank) will be sampled before and 24 h after each exposure.
In Sub-experiment 2, the remaining fish after the repeated exposure experiment will be subjected to an acute stress challenge through increased density for 1 hr. Thereafter, physiological responses to stress will be evaluated at 2, 6, 24 and 48 hr after the challenge by collecting plasma and tissue samples.
We are establishing the credential of PAA as a potential treatment for AGD in salmon, which excludes any possibility for replacement of experimental animals. However, we have merged several questions and hypotheses into one experiment divided into two interconnected sub-trials. The number of fish included in this study has been kept to a minimun (total 360) that is expected to provide robust and statistically relevant analyses. The experiment uses only small tank units (900-L). This will reduce the number of fish needed for the experiment.