Combined impacts of organophosphate pesticide and polyamide microplastics on growth, hematology, and immune responses in juvenile striped catfish (Pangasianodon hypophthalmus)

Organophosphate pesticides and microplastics are two major threats to freshwater ecosystems. Individually, their impacts on aquatic animals are well established, but their combined effects remain poorly understood. Yet, in the Anthropocene, multiple pollutants simultaneously affect aquatic organisms, and their combined effects may not be additive. It is therefore important to study the interactive effects of multiple stressors on aquatic animals. This study examined the effects of sub-lethal concentrations of the pesticide fenitrothion (0.60 mg/L) and polyamide microplastics (10 mg/L) on survival, growth, hematology, and immune-gene expression in juvenile striped catfish (Pangasianodon hypophthalmus) over 28 days. Fish were exposed to microplastics (MP), fenitrothion (Fen), both stressors combined (Fen + MP), or neither (control). Co-exposure to fenitrothion and microplastics (Fen + MP) led to increased microplastic accumulation, reduced growth performance (weight gain, specific growth rate, and feed efficiency), lower survival rates, and significant hematological changes, including elevated glucose (143.89 mg/dL) and reduced hemoglobin (7.30 g/dL). Cellular and nuclear abnormalities, such as micronuclei and teardrop-shaped cells, were most pronounced in Fen + MP treatments. Histo-pathological analysis revealed severe tissue damage in gills, liver, kidney, and intestines under co-exposure. Immunologically, Fen + MP upregulated interleukin-1β (IL-1β) expression but downregulated major histocompatibility complex-II (MHC-II) and interferon genes (IFN-α2, IFN-β2). These findings highlight that combined exposure to the chosen pesticides and microplastics exacerbates physiological, cellular, and immune impairments in striped catfish, posing significant risks to their health and survival.