Evaluation of oregano essential oil (Origanum heracleoticum L.) on growth, antioxidant effect and resistance against Aeromonas hydrophila in channel catfish (Ictalurus punctatus)

Carvacrol and thymol are the two main active components of oregano essential oil (OEO). In this study, the effect of carvacrol and thymol was evaluated separately, in combination and in their natural composition as natural OEO. A total of five treatments, i.e., negative control group, carvacrol, thymol, a combination of carvacrol and thymol and Orego-Stim® (OS, commercial product containing natural OEO from Origanum heracleoticum L.) were added to the diets of channel catfish (Ictalurus punctatus) to investigate the effects of the respective treatments on the growth performance and antioxidant activity. After eight weeks of feeding, fishes were infected with Aeromonas hydrophila and mortality was recorded. Results of this study showed that channel catfish fed with natural OEO (OS), containing a combination of carvacrol, thymol and other minor constituents, significantly enhanced growth performance, which was the highest amongst all treatments (P < 0.05). The addition of OS also effectively enhanced hepatosomatic index (HSI), viscerosomatic index (VSI) and condition factor compared to the control diet (P < 0.05) and distinctly promoted the sedimentation of muscle protein. OS also remarkably enhanced the antioxidant activity of channel catfish. Both the combination of carvacrol and thymol and OS reduced fish mortality following A. hydrophila infection, but the lowest mortality was observed in the group fed with OS. It can be concluded that OS, which contains natural OEO extracted from O. heracleoticum L., can act as a growth promoter, increase antioxidant activity, enhance muscle protein sedimentation and also improve disease resistance to pathogens when added to channel catfish feed.