Impact of dietary administration of Himalayan nettle (Urtica ardens) on histological architecture and gene expression related to growth and immunity in common carp (Cyprinus carpio) fingerlings

Overuse of chemicals in aquaculture practices has raised serious concerns regarding the environmental impact and health implications of chemical-based feed additives, resulting in the search for natural alternatives. The present study investigated the effects of ethanolic extract of Himalayan nettle ( Urtica ardens ) leaf extract as dietary supplementation on the gene expression of genes responsible for growth and immunity, and histological structures of common carp ( Cyprinus carpio ). Experimental diets were formulated for five groups by supplementing various percentages of the nettle extract (0, 0.3, 0.6, 0.9, and 1.2%) into a basal feed (38% crude protein). Common carp fingerlings with an average weight of 16.03 ± 1.83 g were randomly assigned to 15 tanks (10 fish/tank; five groups; triplicate groups per treatment) and fed on formulated diets for 90 days. Histological analysis revealed reduced hepatic lipid vacuolation and enhanced intestinal villi morphology. The gene expression analysis showed upregulation of growth-related genes ( GH , IGF1 , IGF2 ) and modulation of immune-related cytokines ( IL1β , IL10 , TNFα ). Molecular docking analysis was performed using receptor structures from the Protein Data Bank and compounds from PubChem, all of which satisfied Lipinski’s rule of five. Significant binding affinities were observed, with 8-Methyl-6-nonenamide showing strong interactions with TLR-2, Ghrelin, and Telomerase; cis-vaccinic acid with NLR-1; and histamine with TLR-3. Hydrogen bond formation at the active sites indicated stable protein-ligand complexes, contributing to molecular recognition and binding specificity. These findings suggest that U. ardens supplementation can enhance growth performance, immune responses, and tissue integrity in common carp, providing a potential natural alternative to synthetic feed additives in aquaculture. • Histological analysis revealed improved intestinal villi morphology and reduced hepatic lipid vacuolation, supporting organ integrity. • TEM demonstrated increased microvilli length and surface area, enhancing nutrient absorption. • Dietary supplementation of Urtica ardens extract enhanced growth in Cyprinus carpio via upregulation of GH , IGF1 , and IGF2 gene expression. • Immunomodulatory effects included IL10 upregulation and IL1β , TNFα downregulation, indicating an anti-inflammatory response. • Molecular docking confirmed strong ligand-receptor interactions, particularly 8-methyl-6-nonenamide with TLR2, Ghrelin, and Telomerase.