Different effects of continuous and pulsed Benzo[a]pyrene exposure on metabolism and antioxidant defense of large yellow croaker: Depend on exposure duration.

This study aims to compare differential effects of continuous and pulsed BaP exposures on metabolism and antioxidant defense in the liver of large yellow croaker. Fish were subjected to BaP for 4 days and 36 days in three exposure regimes with the same time-averaged concentration of BaP: 4 µg/L BaP continuously, 8 µg/L BaP for 24 h every other day or 16 µg/L BaP for 24 h every 4 days. Our results showed that compared to pulsed BaP exposures, continuous BaP exposure reduced BaP metabolism (CYP1A, CYP3A and AHR transcriptional expressions, GSH content, GSH/GSSG ratio, EROD and GST activities) and antioxidant defense (T-SOD activity) on day 4, resulting to the increases in MDA and PC contents, indicating that continuous BaP exposure induced more severe oxidative damage during the early stage of exposure. But continuous BaP exposure reduced MDA and PC contents by improving BaP metabolism and antioxidant defense during the late stage of exposure. CYP1B transcriptional expression and CAT activity were unsuitable biomarkers of both continuous and pulsed BaP exposures. In conclusion, our results demonstrated differential effects of continuous and pulsed exposures on BaP metabolism and antioxidant responses, which were depend on exposure duration.

Different cold tolerances among three strains of large yellow croaker: related to antioxidant defense and energy metabolism.

The aim of this study was to compare low-temperature tolerances in different strains of large yellow croaker. Dai Qu (DQ), Min-Yue Dong (MY), and Quan Zhou (NZ) strains of large yellow croaker were subjected to cold stress (8.6 °C) for 12 h, 24 h, 48 h, and 96 h. Survival rate, histological observation, and antioxidant and energy metabolism indicators were determined. The results showed that compared with the DQ group and MY group, NZ group aggravated hepatic structure, enhanced ROS, lactate, and anaerobic metabolism (PK gene expression and activity), while inhibited ATP, GSH, antioxidant enzymes (mRNA levels and activities of SOD, GPx, and CAT), and aerobic metabolism enzymes (mRNA levels and activities of F-ATPase, SDH, and MDH), indicating the reduction of cold tolerance in the NZ group was closely correlated with the decrement of antioxidative capacity and energy metabolism efficiency. Nrf2 and AMPK gene expressions were correlated with antioxidant and energy metabolism mRNA levels, respectively, suggesting Nrf2 and AMPK might participate in the modulation of target genes during the cold-stress adaptation. In conclusion, low temperature tolerance of fish depended on the antioxidant defense and energy metabolism efficiency, which contributes to understanding the underlying mechanisms of cold adaptation in large yellow croaker.