Abstract
In the present study, antioxidant activity, immune responses, and growth performance of rainbow trout (Onchorhynchus mykiss) juveniles fed with diets supplemented with dandelion (Taraxacum officinalis) and lichen (Usnea barbata) extracts were assessed. Four different concentrations of aqueous methanolic extract of the plants (0% (control), 0.1%, 0.5%, and 1% (D, dandelion; L, lichen) were added to the diets, and fish were fed for 75 days. On the 15(th), 45(th), and 75(th) day of the study, liver antioxidant enzyme activities were determined, and immune responses were determined every 15(th) day. The results showed that SOD activity increased in the fish group of 0.1% D on the 15(th) and 45(th) day compared to control; however, it was lower in all the lichen extract-treated groups than in control at almost all sampling times, except on the 15(th) day in the 0.1% L group. CAT activity showed an increased value (P < 0.05) in 0.5% L and 1% L treated fish groups on the 15(th) day, in fish of 1% D and 1% L groups on 45(th) and on 75(th) day in 0.1% D group. GPX activity increased on the 15(th) day of the study in fish of 0.1% D group, on the 45(th) day in 1% D and 1% L groups and on the 75(th) day in fish of 0.5% D, 0.1% D, and 0.5% L groups (P < 0.05). G6PDH enhanced in all treatment groups compared to control on the 15(th) day, except in 0.1% L and 0.5% L groups. An elevated G6PDH activity was also observed on the 75(th) day of the study in 0.5% D, 1% D, and 0.5% L fish groups. An increase on lipid peroxidation (LP) was observed in all L groups on the 45(th) day of the study. Lysozyme activity was determined to be the highest in 0.5% and 1% L on the 45(th) day, in 0.1% L on the 60(th) day and in the 0.5% L fish group on the 75(th) day compared to control (P < 0.05). Myeloperoxidase was found to be the highest at the end of the study in 1% L fish group compared to the control (P < 0.05). In conclusion, we suggest the use of dandelion to combat oxidative stress and to lower FCR and the use of lichen to modulate the immune response in rainbow trout. The use of such products will be economical for aquaculture and harmless for the environment.