Turning waste into growth: dietary use of pistachio hull essential oil in common carp aquaculture

This study evaluated the use of pistachio hull essential oil (PEO) as a sustainable dietary ingredient for common carp (Cyprinus carpio). Pistachio hulls are an underutilized agro-industrial by-product with potential functional value in aquafeeds. The essential oil was extracted by hydrodistillation and characterized using GC–MS analysis. Diets containing 0, 1, 2, 4, and 10 g kg⁻¹ PEO were fed to 225 juvenile common carp (8.7 g) in 15 tanks for 60 days. Growth, feed utilization, hematological and serum biochemical parameters were analyzed. Moderate PEO inclusion (4 g kg⁻¹ ) improved growth and feed efficiency, whereas 10 g kg⁻¹ reduced performance. The responses followed nonlinear dose-dependent patterns. Moderate PEO inclusion (4 g kg-1) improved growth and feed utilization, whereas 10 g kg-1 reduced performance. These improvements followed a non-linear (cubic) trend, as confirmed by polynomial contrast analysis (P < 0.05). Hematological and biochemical indicators also showed improvements at moderate PEO levels and signs of physiological stress at the highest dose. Blood biochemistry showed nonlinear patterns: glucose and liver enzymes such as Glutamate oxaloacetate transaminase (GOT), Glutamate pyruvate transaminase (GPT) and Alkaline phosphatase (ALP) were lowest at moderate doses and elevated at 10 g kg⁻¹, suggesting a disruption in physiological homeostasis or potential hepatotoxicity at higher doses; total protein, albumin, globulin, triglycerides, and cholesterol peaked or dipped similarly. Gene expression supported these findings, with moderate PEO enhancing both growth-related and immune-related markers. Further studies should explore long-term effects and species-specific responses. Overall, 4 g kg⁻¹ appears to be an optimal inclusion level for improving carp growth and health, demonstrating the potential of pistachio hulls as a value-added component in sustainable aquafeeds.