Effects of Total Residual Oxidant on Oxidative Stress in Juvenile Olive Flounder Paralichthys Olivaceus

Abstract

ABSTRACTWe investigated oxidative stress in olive flounder Paralichthys olivaceus induced by exposure to total residual oxidant (TRO) at three different concentrations (20, 40, and 60 μg/L) over 14 days to determine concentrations of TRO appropriate for aquaculture. We analyzed survival rate, antioxidant enzyme (superoxide dismutase [SOD] and catalase [CAT]) mRNA abundance, and heat shock protein 70 (HSP 70) expression (mRNA and protein) in the gills and liver, in addition to levels of hydrogen peroxide in plasma. Furthermore, terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) was used to measure apoptosis in the gills. All flounder exposed to 40 and 60 μg/L TRO died by day 14 and day 7, respectively. Antioxidant enzyme mRNA and HSP 70 expression (mRNA and protein) in the gills and liver significantly increased with increasing TRO concentration but decreased on day 14 in the 20 μg/L TRO group. In the gills, TUNEL-positive cells increased, and histological modifications were observed at 40 and 60 μg/L TRO; however, these differences were not observed in the 20 μg/L TRO group. These results indicate that 20 μg/L TRO does not significantly affect olive flounder survival after 14 days or the indicators of oxidative stress between 7 and 14 days. This target concentration of TRO (TRO 20) may be suitable for water treatment in recirculating aquaculture systems containing olive flounder.