The Effects of Continuous Acoustic Stress on ROS Levels and Antioxidant-related Gene Expression in the Black Porgy (Acanthopagrus schlegelii)

Abstract

Hao-Yi Chang, Tzu-Hao Lin, Kazuhiko Anraku, and Yi Ta Shao (2018) Short-term exposure to strong underwater noise is known to seriously impact fish. However, the chronic physiological effects of continuous exposure to weak noise, i.e. the operation noise from offshore wind farms (OWF), remain unclear. Since more and more OWF will be built in the near future, their operation noise is an emerging ecological issue. To investigate the long-term physiological effects of such underwater noise on fish, black porgies (Acanthopagrus schlegelii) were exposed to two types of simulated wind farm noise-quiet (QC: 109 dB re 1 μPa / 125.4 Hz; approx. 100 m away from the wind turbine) and noisy (NC: 138 dB re 1 μPa / 125.4 Hz; near the turbine)-for up to 2 weeks. Measurement of auditory-evoked potentials showed that black porgies can hear sound stimuli under both NC and QC scenarios. Although no significant difference was found in plasma cortisol levels, the fish under NC conditions exhibited higher plasma reactive oxygen species (ROS) levels than the control group at week 2. Moreover, alterations were found in mRNA levels of hepatic antioxidant-related genes (sod1, cat and gpx), with cat downregulated and gpx upregulated after one week of QC exposure. Our results suggest that the black porgy may adapt to QC levels of noise by modulating the antioxidant system to keep ROS levels low. However, such antioxidant response was not observed under NC conditions; instead, ROS accumulated to measurably higher levels. This study suggests that continuous OWF operation noise represents a potential stressor to fish. Furthermore, this is the first study to demonstrate that chronic exposure to noise could induce ROS accumulation in fish plasma.

Keywords: Antioxidant; Auditory evoked potential; Black porgy; Reactive oxygen species; Underwater noise.

Fig. 1.

Fig. 1. Acoustic characteristics of the noise perturbation experiment. The 1/3-octave band spectral characteristics of the noisy condition (NC; solid line with open circles), quiet condition (QC, dashed line with open squares), ambient noise (control, CC, dotted line with open triangles) and the hearing curve of the black porgy (dashed line with solid triangles) (Means ± SEM are shown). N = 5 at each frequency in the audiogram.

Fig. 2.

Fig. 2. The effects of exposure to the underwater noise on plasma (A) cortisol and (B) ROS levels during the 2-week treatment period. NC (solid line), QC (dashed line) and CC (dotted line). Means ± SEM are shown. N = 5 for initial control and N = 10 for all other groups. The measured samples were randomly selected from each treatment pool. *Mann-Whitney U-tests p < 0.05. Solid bracket indicates comparisons between two groups at the same time point; dotted bracket indicate the comparison of the same group between different time points.

Fig. 3.

Fig. 3. Relative expression levels of the indicated genes in fish exposed to wind turbine noise. (A) hepatic sod1 mRNA levels; (B) hepatic cat mRNA levels; (C) hepatic gpx mRNA levels. Means ± SEM are shown. # indicated the group N = 8, in all other groups N = 10. The measured samples were randomly selected from each treatment pool. One-way Kruskal-Wallis ** p < 0.005 or * p < 0.05. Solid bracket indicates comparisons between two groups at the same time point. Values with different letters differ from each other in the same group (CC, NC or QC) (one-way Kruskal-Wallis p < 0.05).