Anthropogenic noise pollution is increasingly acknowledged as a major threat to marine ecosystems, especially for sound-sensitive species, such as the large yellow croaker (Larimichthys crocea). While the effects of underwater noise on fish behavior and physiology have been well-documented, its influence on oxygen metabolism across varying temperatures remains poorly understood. This study examines the impact of boat noise on the oxygen consumption rate (OCR) of juvenile large yellow croakers at different temperatures, a key factor in their metabolic activity. The underwater noise generated by a fishing boat spans a broad frequency range, with a peak spectrum level of 130 dB re 1 µPa at low frequencies between 100 and 200 Hz. Our findings reveal that boat noise significantly elevates the OCR of juvenile fish, with mass-specific OCR increasing by 65.0%, 35.3%, and 28.9% at 18 °C, 25 °C, and 30 °C, respectively. Similarly, individual OCR rose by 60.7%, 35.3%, and 17.1% at these temperatures. These results demonstrate that boat noise triggers a stress response in fish, resulting in heightened metabolic demands across different seasonal conditions. Notably, the impact of boat noise on respiratory metabolism is most significant at lower temperatures. In aquatic environments with stable oxygen levels, the noise-induced rise in oxygen consumption could lead to hypoxia and provoke maladaptive behavioral changes in fish.

The rapid expansion of offshore wind farms (OWFs) is reshaping coastal soundscapes through operational turbine noise, while the acoustic responses of soniferous fishes within operational wind-farm areas remain difficult to assess using conventional fishery surveys. In this study, passive acoustic monitoring (PAM) was deployed within the Yangjiang Offshore Wind Farm to examine short-term associations among underwater sound fields, turbine spatial layout, a turbine startup event, and putative fish-call activity. Fish-call detections were lower along the transect with 550 m turbine spacing than along the 1300 m transect, coinciding with higher measured sound pressure levels in the 550 m spacing layout. Acoustic activity in the central zone of the 1300 m array was 6.46 times higher than that of the 550 m layout, suggesting that lower-noise areas within wind farms may provide favorable acoustic conditions for detectable fish-calling activity. During a turbine startup event, fish-call detection rates temporarily decreased during the transient increase in sound pressure level and subsequently recovered as the underwater noise returned toward baseline conditions. These patterns indicate that PAM can capture short-term soundscape-associated variation in fish-calling activity or call detectability. We further propose a conceptual trade-off framework in which foundation-associated habitat benefits and operational noise may jointly shape the acoustic space use of soniferous fishes in OWFs.

This study investigated the effects of glycerol monolaurate (GML) on the growth performance, physiological efficacy, intestinal structure, and microbiota of hybrid juvenile ♀ Epinephelus fuscoguttatus × ♂ E. lanceolatus. A total of 594 groupers were administered diets supplemented with 0, 2, 4, 6, 8, or 10 g/kg of GML over an 80-day period. The findings indicated that the group receiving 4 g/kg GML supplementation demonstrated significantly enhanced growth performance, as evidenced by increased weight gain, specific growth rate, and a reduced feed conversion ratio compared with the control and other experimental groups. This growth enhancement was associated with elevated catalase and glutathione levels, suggesting improved antioxidant capacity that may contribute to enhanced immune function. Furthermore, fish in the 4 g/kg group exhibited increased digestive enzyme activity and significantly improved intestinal morphology, characterized by thicker muscular layers and a greater fold width and height. Furthermore, compared with the control group, GML supplementation elevated the relative abundance of Proteobacteria while reducing that of Firmicutes at the phylum level. At the genus level, GML markedly suppressed the relative abundance of Mycoplasma and Vibrio. These compositional alterations are potentially linked to improved energy acquisition and a decreased risk of pathogenic infections. Collectively, these results reveal that GML acts as a promising functional feed additive to boost growth performance, optimize digestive capacity, and sustain intestinal structural integrity in hybrid grouper. Based on these results, the optimal GML supplementation dose was determined to be 4 g/kg, providing valuable insights into the role of GML in aquaculture practices for hybrid grouper.