Supplementation Effect of Dietary Carvacrol and Thymol Polyphenols from Oregano Origanum vulgare on Growth Performance and Health Condition of Pacific White Shrimp Litopenaeus vannamei

Two growth trials were conducted for 60-days using aquaria tanks (growth trial 1) and 50-days using commercial culture tank (growth trial 2) to assess the potential effect on using phytogenic feed additives (Regavit AquaTM, Ecopharm Hellas, Greece) containing thymol and carvacrol extracted from Oregano plant Origanum Vulgare (OP) by incorporating the OP powder into the diet formulation for trial 1 and top-dressing process of OP liquid for trial 2. The antimicrobial properties of carvacrol and thymol polyphenols were also determined by using minimum inhibitory concentration (MIC) analysis against Vibrio harveyi and Vibrio parahaemolyticus. From the aquaria tank (trial 1), the growth performance, including final average body weight (ABW), percentage weight gain (PWG) and thermal growth coefficient (TGC) of group of shrimp fed with OP were compared to the control treatment. Using top-dressing process (trial 2), the top coating process to the commercial diet enhance the growth performances of shrimp treated with OP compared to the control treatment. From, trial 1, there was clear evidence for elevated hemocyte activity and increased lysozyme in shrimp fed diets supplemented with OP compared to the control treatments.  MIC analysis performed in the present study also revealed the ability of OP to inhibit the growth of bacteria at the concentration of 2 × 101 µg mL-1. The results indicate that the inclusion of OP up to 0.6% both in direct inclusion within the diet or using top-dressing process significantly increases the growth and non-specific immune in white shrimps L. vannamei.