Evaluation of oregano (Origanum vulgare L.) essential oil effect on growth indices and fillet quality of rainbow trout (Oncorhynchus mykiss) during refrigerated storage (4±1 °C)

  This study evaluated the effects of diets including different levels of oregano (Origanum vulgare L.( essential oil on growth indices and fillet quality of rainbow trout (Oncorhynchus mykiss) during refrigerated storage (4±1°C). For this purpose, rainbow trout with an average weight of 69.38±0.44 g were fed with diets containing 0, 250, 500 and 750 mg kg-1 oregano essential oil for 48 days. After the end of 48 days, growth parameters were measured and also some fishes of experimental groups were filleted and stored at refrigerator (4±1˚C) for 21 days due to quality investigation. Total psychrophilic counts, TBA and TVB-N analyses were done every 7 days (day 0, 7, 14 and 21). The results showed significant differences in some growth parameters including final weight, weight gain, weight gain percent and feed conversion ratio among experimental groups (P<0.05).The results also showed lower amount of total psychrophilic counts and TBA in rainbow trout fillet from oregano groups than control group, during refrigerated storage(P<0.05). As on day 21, the highest amount of PTC was obtained in control (14.39±0.12 log cfu/g) and the least amount of that was obtained in 250 mg kg-1 (12.38±0.09 log cfu/g).The highest amount of TBA was also observed in control (1.57±0.05 log cfu/g) and the least amount of that was observed in 750 mg kg-1 (1.20±0.08 log cfu/g) (P<0.05). No significant differences were observed among essential oil treatments. Overally, it could be say using500 mg oregano essential oil can cause improvement of growth and rainbow trout fillet quality during refrigerated storage (4±1°C).