Oxidative stress, histopathological alterations and anti-oxidant capacity in different tissues of largemouth bass (Micropterus salmoides) exposed to a newly developed sodium carbonate peroxyhydrate granular algaecide formulated with hydrogen peroxide

Abstract

Various strategies exist to control noxious cyanobacterial populations, although the application of a newly developed granular compound (sodium carbonate peroxyhydrate 'SCP', trade name 'PAK® 27' algaecide) containing hydrogen peroxide (H₂O₂) as the active ingredient, has been recently proven as an effective and ecofriendly treatment. However, in aquaculture settings the application of SCP to treat cynobacterial blooms may affect non-targeted biota, such as fish due to H₂O₂ being known to elicit toxic oxidative stress. Consequently, a better understanding of the side effects as a function of dosing concentrations would help to improve treatment efficacy and fish welfare. Thus, the aim of the current study is to assess the potential risks of SCP to largemouth bass (Micropterus salmoides), a high priced fish in the U.S. To this end, fish were exposed to two recommended doses of SCP corresponding to either 2.5 or 4.0 mg/L H₂O₂ for 6 days, with a control group in parallel. After 6 days, the effect of SCP exposure on oxidative stress, histopathological changes and anti-oxidant potential in the brain, liver, gills and muscle were investigated. Results show that exposure to 4.0 mg/L H₂O₂ -SCP incited oxidative damage, evidenced by an over-accumulation of H₂O₂ and malondialdehyde (MDA) in the brain and liver, which were accompanied by an increment in xanthine oxidase activity. Unlike 4.0 mg/L H₂O₂, these oxidative stress biomarkers in the brain and liver tissue of 2.5 mg/L H₂O₂-SCP exposed fish were restrained within control levels and concomitant with an increase in superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), glutathione reductase (GR) and glutathione-s-transferase (GST) activity. In contrast, many of these anti-oxidants sentinels in the 4.0 mg/L H₂O₂ exposed fish were either unaffected or significantly inhibited, which resulted in over-accumulation of H₂O₂ and MDA. In addition, a series of histopathological alterations were observed, and the most severe brain injuries and liver inflammation were recorded in 4.0 mg/L H₂O₂-SCP exposed fish. Based on oxidative parameters, both SCP doses resulted in a relatively mild oxidative stress in gills but no effect in muscle, probably explaining the modest anti-oxidative responses in the former and almost complete lack of anti-oxidative responses in the latter. Overall, our findings suggests that the application of SCP at 4.0 mg/L H₂O₂ to control cyanobacterial blooms in aquaculture settings can possess potential risks to the farmed fish.

Keywords: Antioxidant defense system; Brain damage; Hemorrhaging; Hydrogen peroxide (H(2)O(2)); Malondialdehyde (MDA); Sodium carbonate peroxyhydrate.