Comparative toxicity of virgin and biodegraded LLDPE microplastics on growth, behavior, antioxidant, and hematological health of Catla catla fish.

Biodegraded microplastics caused less disruption to fish growth, behaviour, antioxidant activity, and haematological health, indicating lower ecological risk. This study evaluated the ecotoxicological effects of virgin linear low-density polyethylene microplastics (VPE) and Bacillus cereus-degraded LLDPE microplastics (BDPE) at concentrations of 1 µg/L, 10 µg/L, 100 µg/L on the freshwater fish Catla catla. Fish exposed to both VPE and BDPE exhibited abnormal behaviors such as irregular swimming, loss of balance, and excessive mucus secretion, especially at higher concentrations. Growth and survival analysis revealed a dose-dependent reduction in weight gain and survival among VPE-treated fish, whereas BDPE-exposed groups showed comparatively better performance, particularly at 1 µg/L. Hematological parameters including red blood cell count, hemoglobin, hematocrit, and mean corpuscular hemoglobin concentration decreased significantly in both VPE and BDPE treatments by day 60, while white blood cell count, mean corpuscular volume, and mean corpuscular hemoglobin increased, with the most pronounced changes observed in VPE-exposed fish. Antioxidant enzyme activities increased on day 20 as an initial stress response, but declined by days 40 and 60, indicating exhaustion of the defense system under prolonged exposure in both VPE and BDPE groups. Overall, VPE microplastics exert greater toxicological effects on Catla catla compared to BDPE, highlighting the potential of microbial degradation in mitigating plastic toxicity in aquatic ecosystems.