Herbal feed additives have benefits in aquaculture, as they can improve growth performance, welfare, and stress resistance. Hence, the effects of dietary Prosopis farcta ex tract (PFE) on the growth parameters, digestive enzyme activity, antioxidant defense, innate immunity responses, and resistance to ammonia stress in the common carp, Cyprinus carpio, were studied. Fish (15.14 ± 0.72 g) were fed on diets without the PFE (PFE0) or those fortified with 0.5% (PFE0.5), 1% (PFE1), or 2% (PFE2) PFE for 60 days and then subjected to ammonia stress for 24 h. The growth rate, feed efficiency, and amylase-, lipase-, and protease-specific activities in the PFE1 and PFE2 treatments showed significant elevations compared to these values in PFE0. The intestinal protease-specific activity significantly increased in all of the PFE treatments compared to that in the PFE0 treatment. Serum total protein and immunoglobulin significantly increased in the PFE1 treatment, whereas serum albumin and alternative complement activity significantly increased in the PFE2 treatment compared to these values in the PFE0 treatment. The PFE2 treatment signifi cantly mitigated post-stress elevations in serum cortisol, glucose, malondialdehyde levels, alanine aminotransferase, and aspartate aminotransferase activities.