A broad-spectrum fungicide, dichlofluanid is widely used in antifouling paints and agricultural pesticides. In this study, the acute and chronic effects of sublethal concentrations, namely, no observable effect concentration (NOEC) and 50% lethal concentration (LC50) of dichlofluanid (1/10 NOEC, NOEC, 1/10 LC50, and LC50) were evaluated on the marine mysid, Neomysis awatschensis. Acute toxicity test (96 h) showed higher sensitivity to dichlofluanid in juvenile mysids (LC50 3.1 μg L−1) than adults (LC50 24.5 μg L−1), with lower survival rate and reduction in food consumption. Exposure with dichlofluanid considerably induced oxidative imbalance, as NOEC (0.006 μg L−1 for juveniles and 0.074 μg L−1 for adults) and 1/10 LC50 values increased intracellular concentrations of malondialdehyde and glutathione, and the enzymatic activities of catalase and superoxide dismutase, whereas exposure to LC50 value decreased the values of oxidative parameters. Enzymatic activity of acetylcholinesterase decreased considerably when exposed to LC50 value. In the case of chronic effects, exposure to NOEC for 4 weeks markedly decreased the juvenile survival rate, while adults showed tolerance. Multigenerational monitoring in response to NOEC showed a significant growth retardation with an increase in intermolt duration as well as a decrease in the number of newborn mysids from females of the third generation. Consistent exposure to environmentally relevant sublethal concentrations of dichlofluanid would be detrimental to mysid individuals and the survival of the mysid population. Display omitted •Dichlofluanid toxicity, for the first time, was evaluated on mysid crustaceans at a multigenerational level.•Dichlofluanid induced oxidative stress with age-specific decrease in survival and food consumption.•Dichlofluanid reduced the antioxidant defense ability and cholinergic response of mysid.•Higher concentrations directly affected mysid growth, molting, and fecundity.•Even sublethal concentrations significantly modulated mysid population when they were exposed consistently.