Toxicological effects of polyethylene microplastics on growth, antioxidant capacity, histopathology and stress-related genes transcription in Asian seabass (Lates calcarifer) larvae

A 10-day study was carried out to examine the effects of polyethylene microplastics (PEMP) on growth, antioxidant capacity, stress-related genes transcription, and gut histology of Asian seabass (Lates calcarifer) (Bloch, 1970) larvae. In this regard, 2 day old post hatch larvae were exposed to four concentrations of PEMP, including 1) control (without PEMP addition), 2) PEMP50 (50 μg PEMP/L), 3) PEMP100 (100 μg PEMP/L) and 4) PEMP500 (500 μg PEMP/L). Two days post hatching larvae (mouth opening time) were distributed into twelve 120-L cylindrical polyethylene tanks, each filled with 100 L seawater (47.0 ± 0.5 g/L, 32 ± 0.8 °C) (2500 larvae in each tank, 25 larvae/L). Different dosages of the PEMP were diluted in ethanol, then added to the larviculture tanks and larvae were exposed to each treatment for 10 days. Each treatment was replicated in three tanks. Rotifers (Brachionus plicatilis small type, 5-10 animals/mL) were offered to larvae from second DPH to 10 DPH in a green water (0.1-0.3 × 10⁶ cell/ml Nannochloropsis. sp) system. The highest and lowest survival rate were in control (28.50 ± 3.38 %) and PEMP500 (3.50 ± 0.12 %) groups, respectively (P < 0.05). The highest body weight was in the control (1.94 ± 0.06 mg) but the lowest body weights were in PEMP100 (1.42 ± 0.03 mg) and PEMP500 (1.35 ± 0.03 mg) groups, respectively. The highest and lowest catalase (CAT) activities were in control and PEMP500 groups, respectively (P < 0.05). Superoxide dismutase (SOD) and glutathione reductase activities decreased with increasing PEMP dosages, meanwhile lipid peroxidation level increased. At day 10, the expression of interleukin-1β, heat shock protein 90, CAT, SOD and glutathione S transferase genes were down-regulated with increasing PEMP in water. The thickness of the gut wall, crypt depth, villus width and height significantly decreased in larvae exposed to PEMP100 and PEMP500 groups compared to the other treatments. Based on the results of the present study, increasing PEMP concentrations in water exert adverse lethal effects during the critical larval development in marine fish species.