Co-exposure to Hexavalent Chromium and Polyamide Microplastics Alters Growth, Hematology, Histopathology of Tissues and Immune Genes Expression in Striped Catfish (Pangasianodon hypophthalmus).

Hexavalent chromium (Cr6+) and microplastics (MP) are considered pervasive pollutants in aquatic environments and its exceeding limit could produce serious cytotoxic effects in fish. In view of that, a 28-day trial was designed where juvenile striped catfish (Pangasianodon hypophthalmus) were subjected to a sub-lethal concentration of chromium (Cr6+; 3.2 mg/L) and polyamide microplastic (PA-MP; 10 mg/L) alone or combined. Three different waterborne treatments i.e. T1 (PA-MP); T2 (Cr6+); and T3 (Cr6++PA-MP) including a control (no Cr6+ or PA-MP) with three replicates for each were incorporated. The results exhibited that the exposure of Cr6+ increased ingestion of PA-MP in T3. Compromised weight gain (g), apparent feed conversion ratio (AFC) and survival percentages were observed in co-exposure group. Blood indices including mean concentrations of hemoglobin and glucose were found to be 1.37- and 1.21-fold higher than those of the control, respectively. The frequencies of nuclear and cellular abnormalities were recorded maximum in T3 (1.64% and 5.08%) and subsequently in T2. However, the co-exposure of Cr6+ and PA-MP escalated the severity of histopathological abnormalities in gills, liver, kidney, and intestine as well. Besides, significantly upregulated expression of Interleukin-1β (IL-1β) mRNA was estimated in T3 (p < 0.05). In contrast, the relative fold change of Major compatibility complex-II (MHC-II), Interferon-γ-α2 (IFN-α2) and Interferon-γ-β2 (IFN-β2) mRNA estimated lowest due to combined exposure. Finally, the overall performance of juvenile striped catfish relatively exacerbated in co-exposure group in terms of its weight gain, feeding efficiency, survival, hemato-biochemistry, histopathological changes and immune-related genes expression based on principal component analysis (PCA).