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¹ Kastamonu University, Faculty of Fisheries and Aquaculture, Department of Basic Sciences, Kastamonu, Turkey
² Atatürk University, Faculty of Medicine, Department of Medical Pathology, Erzurum,Turkey
³ Çanakkale Onsekiz Mart University, Marine Science and Technology Faculty, Depertmant of Aquaculture, Çanakkale, Turkey
⁴ University of Miyazaki, Interdisciplinary Graduate School of Agriculture and Engineering, Japan
⁵ Atatürk University, Faculty of Fisheries and Aquaculture, Department of Aquaculture, Erzurum, Turkey DOI : 10.4194/1303-2712-v15_4_04 Viewed : 7421 - Downloaded : 6107 A feeding trial was performed to assess any beneficial effect of three herbal oils; mint, thyme and sage oils containing 74 g kg-1 pulegone, 77 g kg-1 carvacrol and 76 g kg-11,8-cineole, respectively on growth performance, survival, fatty acid composition, and liver and kidney histology of rainbow trout (Oncorhynchus mykiss). Herbal oils were added at 0.5 %, 1.0% and 1.5 % concentrations to a fish meal-based control diet, and each diet was fed to triplicate groups of rainbow trout fingerlings for 60 days with growth parameters recorded weekly. Results showed that FCR was affected negatively in all mint oil diet fed groups where it was higher than that of control and other groups (P<0.05). The lowest FCR values were recorded in the thyme and sage oil containing diets fed groups (P<0.05) with no significant differences between these two groups. SGR was also found lower in mint oil groups than in control. The highest SGR was recorded in thyme and sage oil fed groups (P<0.05). Survival was similar in fish fed with diets containing thyme, sage oil and control diet (P>0.05). However, survival was the lowest in fish fed with mint oil supplemented diets(P<0.05). Whole body fatty acid profiles except total saturated fatty acids are closely influenced by dietary herbal oil administrations. Total polyunsaturated n-6 fatty acid was lowest in 1 %thyme oil and all sage oil diet fed groups (P<0.05). Total polyunsaturated n-3 fatty acid was similar between control and sage oil supplemented groups, but in other groups it was significantly decreased (P<0.05). EPA/DHA ratio was observed significantly low in 1.5 %thyme oil and all groups of sage oil fed fish. There were no histological differences observed in liver or kidney of fish fedwith control and 0.5 % and 1 % thyme and sage oil supplemented diets.The present results showed positive effects of thyme and sage herbal essential oil supplemented diets on growth performance and fatty acid utilization and these oils may be useful feed supplements in production of rainbow trout. Keywords : Rainbow trout, feed additive, herbal oil, growth performance, survival, fatty acid composition