Effects of polyethylene microplastics on immune function and bacterial disease resistance in Israeli carp (Cyprinus carpio)

Microplastics (MPs) have emerged as major environmental pollutants in aquatic ecosystems due to their widespread distribution and persistence. However, research on the effects of MP exposure on major freshwater aquaculture species remains limited. We evaluated the effects of polyethylene MPs (MPEs; 34–50 μm) on innate immune responses, serum biochemical parameters, cytokine gene expression, growth performance, and resistance to edwardsiellosis in Israeli carp ( Cyprinus carpio ) following 21 days of exposure to 0, 0.01, 0.1, and 1 mg/L MPEs under laboratory conditions. Serum lysozyme activity was significantly decreased in the 0.1 and 1 mg/L MPE-treated groups, while serum alternative complement activity and the phagocytic activity of head kidney leukocytes were significantly decreased in the 1 mg/L group. Conversely, serum glucose levels and pro-inflammatory cytokine gene expression in head kidney tissue were significantly increased following MPE exposure. Serum alkaline phosphatase activity exhibited transient elevation in the 1 mg/L group, whereas serum aspartate transaminase, alanine aminotransferase, and total protein levels showed no significant changes. Growth performance, including weight gain, specific growth rates, and feed efficiency, was significantly reduced in fish exposed to 0.1 and 1 mg/L MPEs. Following challenge with Edwardsiella tarda , cumulative survival rates in the 0.1 and 1 mg/L groups were > 20% lower than those in the control group. The lower post-challenge survival rates observed at higher MPE concentrations indicate that MPE exposure may impair immune function, induce physiological stress, and reduce growth performance in Israeli carp.