Publication
Alterations in mucosal structures and key regulatory molecules of oxidative stress in Atlantic salmon (Salmo salar L.) induced by amoebic gill disease and oxidant-based chemotherapeutic interventions
| Summary: | Amoebic gill disease (AGD), a parasitic infestation caused by the ectoprotozoan Neoparamoeba perurans, is a serious problem in Atlantic salmon (Salmo salar) farming. Current treatments strategies (i.e. freshwater and hydrogen peroxide bathing) present several issues (economic cost, logistics, AGD resolution and animal welfare). Therefore, peracetic acid (PAA), a powerful oxidant, is a possible good alternative since it degrades rapidly into innocuous residues, requiring a short contact time and it is effective in low concentration against several microorganisms. In this study, the efficacy of PAA in treating AGD and the physiological response of salmon during treatment were investigated. AGD in smolts was experimentally induced and when the gill score (GS) reached 1-2, fish were treated with PAA via bath exposure. Three commercial PAA products were tested (Perfectoxid, AquaDes and ADDIAqua) at a concentration of 5 ppm. Two exposure durations were evaluated, 30 mins and 60 mins. Sampling was performed 1 day and 2 weeks after treatment. The reactive oxygen species (ROS) levels in plasma increased through time, especially in the groups treated for 30 mins. The groups exposed to AquaDes and Perfectoxid for 30 mins had higher ROS levels than the infected-untreated group (IUC) two weeks post-treatment. No significant differences in total plasma antioxidant capacity (TAC) were found among the treatments and between sampling points. 13 biomarkers for oxidative stress were evaluated in the gills and olfactory organs. Overall, PAA treatments resulted in the modulation of the expression of the marker genes. Parasitism alone did not cause significant changes in gene expression in the olfactory rosette, though treatment-induced regulation was found. In the gills, infection downregulated most of the genes and the majority remained so even after PAA treatment. In the olfactory rosette, PAA did not changed the organ’s condition, in relation to IUC. In the gills, treatment considerably reduced the proportion of damaged tissues in almost all groups. Mucosal organs responded to parasitism and PAA treatment in different ways. This study demonstrated that PAA treatment of AGD in salmon smolts resulted in quite varied response profiles. Disease resolution was not fully established as assessed by visual pathology, histopathology and qPCR, though there were indications that the type of PAA product might play a role in its treatment efficacy. |
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| Main Authors: | Furtado, Francisco Machado Faria |
| Subject: | AGD Aquaculture Oxidative stress Mucosal immunity AGD Aquacultura Imunidade da mucosa Saúde dos peixes Stress oxidativo |
| Year: | 2022 |
| Country: | Portugal |
| Document type: | master thesis |
| Access type: | open access |
| Associated institution: | Universidade de Lisboa |
| Language: | English |
| Origin: | Repositório da Universidade de Lisboa |
| Summary: | Amoebic gill disease (AGD), a parasitic infestation caused by the ectoprotozoan Neoparamoeba perurans, is a serious problem in Atlantic salmon (Salmo salar) farming. Current treatments strategies (i.e. freshwater and hydrogen peroxide bathing) present several issues (economic cost, logistics, AGD resolution and animal welfare). Therefore, peracetic acid (PAA), a powerful oxidant, is a possible good alternative since it degrades rapidly into innocuous residues, requiring a short contact time and it is effective in low concentration against several microorganisms. In this study, the efficacy of PAA in treating AGD and the physiological response of salmon during treatment were investigated. AGD in smolts was experimentally induced and when the gill score (GS) reached 1-2, fish were treated with PAA via bath exposure. Three commercial PAA products were tested (Perfectoxid, AquaDes and ADDIAqua) at a concentration of 5 ppm. Two exposure durations were evaluated, 30 mins and 60 mins. Sampling was performed 1 day and 2 weeks after treatment. The reactive oxygen species (ROS) levels in plasma increased through time, especially in the groups treated for 30 mins. The groups exposed to AquaDes and Perfectoxid for 30 mins had higher ROS levels than the infected-untreated group (IUC) two weeks post-treatment. No significant differences in total plasma antioxidant capacity (TAC) were found among the treatments and between sampling points. 13 biomarkers for oxidative stress were evaluated in the gills and olfactory organs. Overall, PAA treatments resulted in the modulation of the expression of the marker genes. Parasitism alone did not cause significant changes in gene expression in the olfactory rosette, though treatment-induced regulation was found. In the gills, infection downregulated most of the genes and the majority remained so even after PAA treatment. In the olfactory rosette, PAA did not changed the organ’s condition, in relation to IUC. In the gills, treatment considerably reduced the proportion of damaged tissues in almost all groups. Mucosal organs responded to parasitism and PAA treatment in different ways. This study demonstrated that PAA treatment of AGD in salmon smolts resulted in quite varied response profiles. Disease resolution was not fully established as assessed by visual pathology, histopathology and qPCR, though there were indications that the type of PAA product might play a role in its treatment efficacy. |
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