The enzymatic and transcriptional adverse effects of hull in-water cleaning discharge on juvenile rockfish (Sebastes schlegeli)

The hull in-water cleaning (IWC) process creates chemical contaminants, including antifouling paint particle mixtures that are directly discharged into the coastal environment. Recent attention has also been paid to the international regulation of ship hull cleaning discharges in environmental media. However, few studies have investigated the adverse effects or toxic pathways on resident marine species. In this study, we evaluated the chemical concentration of IWC discharge in situ and its toxic effects on juvenile rockfish (Sebastes schlegeli), a major coastal fishery resource, using enzymatic and transcriptomic studies. Zinc (8.05 ± 0.96 to 189.96 ± 47.76 μg/L) was the most abundant substance in IWC discharge, followed by copper (0.87 ± 0.19 to 1.97 ± 0.60 μg/L). No mortality was observed after 7 days of exposure in any experimental group; however, reactive oxygen species and acetylcholinesterase activity varied in juvenile rockfish exposed to the highest concentration of IWC discharge (10-fold-diluted IWC discharge). The immune and detoxification systems in juvenile rockfish exposed to IWC discharge were also significantly affected in juvenile rockfish exposed to 10-fold-diluted IWC discharge (zinc: 189.96 ± 47.76 μg/L, copper: 1.97 ± 0.60 μg/L). The expression of genes related to oxidative stress, including Cu/Zn-SOD, GST, and CAT, increased significantly in fish in all the exposure groups. Specifically, brain transcriptomic analysis revealed disturbances in the nervous system and homeostatic processes. Although lethal toxicity was not significantly affected, these findings indicate the potential hazard posed by sub-lethal concentrations of IWC discharge to juvenile fish, which are at a high-level in the food chain. Our enzymatic and transcriptomic results showed that Zn-dominant IWC discharge exposure may cause neuronal and immune toxicity in marine fish species, providing relevant insights into the management of hull IWC discharge to protect coastal ecosystems against chemical contaminants.