The study of the effects of adding Eucalyptus (Eucalyptus globules) and Thyme (Zataria multiflora) to juvenile Rainbow trout (Oncorhynchus mykiss) diet on growth factors and intestinal microflora

Studies which have been done about effects of herbs on reinforcing and stimulating the immune system in aquatic against pathogens indicate their considerable impacts. Herbs usage is becoming more common because they are cheap, with no side effects for fish, human and the environment. The aim of this research is to add essential oils of eucalyptus (Eucalyptus globules) and thyme (Zataria multiflora) to juvenile rainbow trout (Oncorhynchus mykiss) diet and to study their effects on survival and growth factors and intestinal microflora. 180 fish (mean weight 5.27 gr) were divided into 6 experimental groups including: 1-The control group (commercial diet without any essential oils of eucalyptus and thyme), 2-Treatment 1 (500 mg thyme essential oil in 1 kg fish feed), 3- Treatment 2 (1000 mg thyme essential oil in 1 kg fish feed), 4- Treatment 3 (mixture of 500 mg eucalyptus essential oil and 500 mg thyme essential oil in 1 kg fish feed), 5- Treatment 4 (500 mg eucalyptus essential oil in 1 kg fish feed) and 6-Treatment 5 (1000 mg eucalyptus essential oil in 1 kg fish feed). Each group was in triplicate. The fish were fed with these diets for 8 weeks in Sefidroud Fisheries Research Station. Growth factors including PBWI, FCR, GR, SGR, K and SR were measured at the end of the feeding trial. Intestinal microbial culture experiments on TSA medium for aerobic and optional anaerobic bacteria in 20C for 3 to 5 days were conducted and the bacteria were counted (CFU) and the data were analyzed by the statistical software. According to the obtained results, adding 0/5 gr thyme essential oil in 1 kg diet led to growth factors and survival rate increase and FCR enhancement. The highest SR was observed in T1 (P>0/05). Intestinal total bacteria level in T5, T4, T3 and T2 was respectively reduced in comparison with that of from T1 and the control group (P<0/05). It can be concluded that intestinal total bacteria decreased and immunity increased by expanding eucalyptus dosage. Results of this study reveal that use of herb essential oils, as feed additives, can be beneficial for fish production and is recommendable to fish farmers and fish feed suppliers.