Evaluation of Himalayan nettle (Urtica ardens) extract meal in common carp (Cyprinus carpio) feed: Impact on growth performance, digestive enzyme activity and antioxidant capacity

This research aims to evaluate the impact of an extract derived from the leaves of Himalayan nettle (Urtica ardens) leaf extract on common carp, Cyprinus carpio, growth, digestive enzymes, fish body carcass composition, antioxidant system, and water quality parameters. For a duration of 90 days, experimental diets containing nettle extract were given to 150 fish (12.38 +/- 0.53 g) in 15 tanks (10 fish per tank). The five groups in triplicate were: control or T-0 (untreated), T-1 (fed 0.3% extract), T-2 (0.6% extract), T-3 (0.9% extract), and T-4 (1.2% extract). Results revealed that nettle extract in the diet increases common carp growth up to 0.9% concentration of extract. Its feed conversion ratio decreases, while weight gain and specific growth rate rise significantly compared to the control diet. No mortality was observed during the 90-day experiment. Dietary nettle extract did not affect whole-body fibre and crude ash percentages (p > 0.05). Nettle-fed and control groups showed significant differences in crude protein, body fat, and total body moisture (p < 0.05). After a 90-day feeding trial, 0.9% nettle extract-fed fish had higher protease, amylase, lipase, and cellulase levels than the control group (p < 0.05). When nettle content reached 1.2%, enzyme activity decreased. Orthophosphate production peaked at 4 and 8 hours after feeding, while ammonia excretion peaked at 2 and 6 hours. The control group excreted the most ammonia and orthophosphate, while the 0.9% group excreted the least. Liver and kidney SOD levels were higher in common carp fed a 0.6% nettle extract diet. Feeding with a 0.9% nettle extract diet improved hepatic lipid peroxidation, gut and liver glutathione. Gut and kidney SOD, catalase, LPO, and GSH increased dramatically on the 1.2% diet. Statistically, the 0.9% nettle extract (T-3) group showed the overall best results compared to the control diet. These findings demonstrate the potential of nettle extract as a dietary supplement in aquaculture.