Ameliorating Nickel-Induced Stress in Hypophthalmichthys molitrix (Silver Carp) Through Piper nigrum Extract Supplementation.

The current study examined the damaging implications of nickel (Ni) toxicity on body composition, growth responses, histology and hematology of Hypophthalmichthys molitrix, as well as the potential mitigating effects of Piper nigrum extract. For this purpose, H. molitrix were distributed into six groups, namely T1, T2, T3, T4, T5, and T6. All treatments were assessed in triplicates. T1 was designated as the negative control treatment, receiving no Ni exposure or dietary supplementation, whereas T2 acted as the positive control treatment, exposed to sub-lethal concentrations of nickel chloride (NiCl₂) at 3.6 mg/L. Groups T3-T6 received diets enriched with 1%, 2%, 3% and 4% P. nigrum extract, respectively and were also exposed to 3.6 mgL^-1 NiCl₂ toxicity. The findings of this investigation revealed that T2 exhibited decreased growth responses, characterized by a weight gain (WG) of 8.12 g, percentage weight gain (WG%) of 77.83% and specific growth rate (SGR) of 0.96. Additionally, T2 displayed altered hematological parameters such as reduced red blood cells (RBC: 1.3 × 10⁶ mm^-3) and hemoglobin levels (Hb: 5.8 g/100 ml), and increased white blood cell counts (WBC: 75.31 × 10³ mm^-3). Also, T2 showed reduced protein (13.14%), fat (2.15%), and moisture content (73.44%), hepatocyte degeneration, and Ni bioaccumulation in hepatic tissues. In contrast, T1 (control negative) and T3 (1% P. nigrum extract) demonstrated improved growth performance with WG of 18.49 g and 16.92 g, respectively. They also showed increased RBC (1.77 × 10⁶ mm^-3 and 2.77 × 10⁶ mm^-3) and Hb levels (9.65 g/100 ml and 8.15 g/100 ml), decreased WBC counts (6.12 × 10³ mm^-3 and 7.79 × 10³ mm^-3), and elevated protein (16.42% and 15.29%), fat (3.22% and 3.11%), and moisture content (76.92% and 76.6%), respectively. Furthermore, liver histological analysis revealed that dietary supplementation with 1% P. nigrum extract (T3) effectively minimized the adverse effects of NiCl2 toxicity, characterized by a normal central vein structure and significantly reduced histological damage. In conclusion, the results show that 1% P. nigrum extract supplementation significantly ameliorates the adverse effects on carcass composition, elevates growth responses, enhances hematological indices, and mitigates the toxic effects of Ni on the histology of H. molitrix. This comprehensive improvement in nutritional quality, growth rates, blood health, and tissue integrity suggests that P. nigrum extract has tremendous potential as a natural remedy for mitigating the adverse effects of Ni toxicity in aquatic species.