The large yellow croaker (Larimichthys crocea),which is an economically important mariculture fish in China,is often exposed to environmental hypoxia.Reactive oxygen species (ROS) homeostasis is essential for the maintenance of normal physiological conditions in an organism.Direct evidence that environmental hypoxia leads to ROS overproduction is scarce in marine fish.Furthermore,the sources of ROS overproduction in marine fish under hypoxic stress are poorly known.In this study,we investigated the effects of hypoxia on redox homeostasis in L.crocea and the impact of impaired redox homeostasis on fish.We first confirmed that hypoxia drove ROS production mainly via the mitochondrial electron transport chain and NADPH oxidase complex pathways in L.crocea and its cell line (large yellow croaker fry (LYCF) cells).We subsequently detected a marked increase in the antioxidant systems of the fish.However,imbalance between the pro-oxidation and antioxidation systems ultimately led to excessive ROS and oxidative stress.Cell viability showed a remarkable decrease while oxidative indicators,such as malondialdehyde,protein carbonylation,and 8-hydroxy-2 deoxyguanosine,showed a significant increase after hypoxia,accompanied by tissue damage.N-acetylcysteine (NAC) reduced ROS levels,alleviated oxidative damage,and improved cell viability in vitro.Appropriate uptake of ROS scavengers (e.g.,NAC and elamipretide Szeto-Schiller-31) and inhibitors(e.g.,apocynin,diphenylene iodonium,and 5-hydroxydecanoate) may be effective at overcoming hypoxic toxicity.Our findings highlight previously unstudied strategies of hypoxic toxicity resistance in marine fish.