Abstract: To evaluate the effects of microplastics on marine fish, we exposed juvenile Lates calcarifer (initial weight 8-12 g, body length 7-10 cm) in polyethylene  and biodegradable  microplastics (3 mm long × 3 mm wide) at an environmental relevant concentration (0.375 n·L^-1) to diet for 45 days. Liver antioxidant enzyme activities and the expression of genes involving in key pathway were measured after microplastics exposure for 30 and 45 days, respectively. The results showed that both types of microplastics could be ingested by fish but did not influence body weight and body length. Antioxidant enzyme activity showed limited responses to microplastics, and only catalase (CAT) decreased significantly in PE group compared after 45 days exposure. After 30 days exposure, all the relative expressions of kelch-like epichlorohydrinassociated protein 1 (Keap1), nuclear factor-E2-related factor 2 (Nrf2), gluthione S-transferase1 (GST1) and heme oxygenase 1 (HO1) increased in both exposure groups but the differences were not statistically significant. There were no significant differences in biological effects between two types of microplastics. Those results indicated that the exposure to microplastics at environmental relevant concentration did not affect the growth and did not cause obvious antioxidant response of juvenile L. calcarifer. Biodegradable microplastics can be ingested by fish and will not be degraded in the short term. If biodegradable microplastics accumulate in the marine environment, they may negatively affect fish in the long term. The current results underlined the need to assess the long-term impacts of biodegradable and conventional microplastics on marine fish.

Key words: Lates calcarifer, biodegradable microplastics, Keap1/Nrf2.