Ameliorating effects of dietary parsley (Petroselinum crispum) on ammonia toxicity in the rainbow trout, Oncorhynchus mykiss: growth, digestive enzymes, immunity, and stress resistance

Use of phytobiotics as immunostimulant is increasing in aquaculture. In this study, the immune and growth promoting effects of parsley extract (PUE) were examined in the rainbow trout. In this regard, the various dietary levels of parsley extract (PUE), Petroselinum crispum (0, 0.5, 1.5, 3, and 4.5%) was added to the diet of rainbow trout to assay its potentials on immunity, growth, digestive enzymes, and mitigating ammonia-induced stress. A total of 450 fish (15.43±0.06 g; mean ± SE) were distributed into fifteen 300-L fiberglass tanks (30 fish per tank) and fed PUE for 60 days and then challenged with unionized ammonia (0.3 mg/l). According to results, PUE mainly at 3−4.5% levels increased the growth, lipase and protease activities, humoral and mucosal immune components and liver antioxidant enzymes activities. These effects were kept even after ammonia stress, where the immune components were higher in PUE-treated fish than the control group. Furthermore, the dietary PUE reduced ammonia-related oxidative stress, as malondialdehyde (MDA) values (as the indicator of lipid peroxidation) decreased in fish fed PUE. The concentrations of liver metabolic enzymes in blood, both before and after ammonia stress declined in the fish fed PUE. Our findings demonstrated the growth and immune boosting and ammonia-stress mitigating properties of PUE in rainbow trout.