Toxicological Effects of Polystyrene Microplastics on Growth, Enzymatic Activity, Hematology, and Tissue Integrity in <scp> <i>Labeo rohita</i> </scp>

Polystyrene microplastics (PS-MPs) are emerging aquatic contaminants with potential toxicological impacts on fish health and aquaculture sustainability. This study evaluated the dose-dependent effects of PS-MPs on growth performance, enzymatic activity, hematological parameters, behavior, nutrient digestibility, and histopathology in Labeo rohita (Rohu). A total of 180 fingerlings were randomly assigned to three groups: control (0 mg/L), low exposure (50 mg/L), and high exposure (100 mg/L), with triplicate tanks (n = 20 fish per tank) over a 21-day period. Exposure to PS-MPs significantly impaired growth performance, as evidenced by reduced weight gain, increased feed conversion ratio, and decreased survival in the high-dose group (p < 0.05). Alkaline phosphatase (ALP) activity in gill and intestinal tissues declined markedly in a dose-dependent manner, indicating compromised metabolic and absorptive functions. Hematological analysis revealed reduced red blood cell count and hemoglobin concentration, alongside elevated white blood cell count, suggesting anemia and stress-induced immune responses. Behavioral alterations, including reduced feeding efficiency, irregular swimming, and increased bottom-dwelling activity, were more pronounced at higher concentrations. Furthermore, nutrient digestibility coefficients for dry matter, protein, fat, and energy decreased significantly with increasing PS-MP exposure. Histopathological examination confirmed severe structural damage in gill and intestinal tissues, including epithelial lifting, lamellar fusion, necrosis, villi shortening, and inflammation. These findings demonstrate that PS-MPs exert multilevel toxic effects on L. rohita (Rohu), disrupting physiological, biochemical, and structural integrity. Overall, this study highlights the ecological and toxicological risks of microplastic contamination in freshwater systems and underscores the need for mitigation strategies to protect aquatic organisms and aquaculture productivity.