Growth performance, hepatic function parameters, histological changes of rainbow trout Oncorhynchus mykiss (Walbaum, 1792) and oxidative stability index of feed following dietary administration of Mix-Oil

The main objective of this study was to evaluate the effects of dietary supplementation of Mix-Oil (including: Thymus vulgaris (%0.5), Origanum vulgare (2%) and Eucalyptus spp. (2.5%) essential oils) on growth performance, hepatic function parameters, tissue changes of rainbow trout and oxidative stability index of trout feed. Four groups of trout fish (with average weight 31.0±0.1 g) were fed with four diets containing: 0, 50, 200 and 400 ppm of Mix-Oil for 8 weeks. SGR, ADG, CF, TGC, DGC, RGR and BWI were significantly higher and also FCR significantly lower were observed in 200 and 400 ppm groups compared to 50 ppm and control groups (p<0.05). Significant increase in PER, LER, FCE and RFI in fish fed with 200 and 400 ppm Mix-Oil were observed compared with control and 50 ppm groups (p<0.05), while, no significant differences having been observed among different treatments in terms of AST and ALT level (p>0.05). An increase in the number of hematopoietic cells in the kidney and significant increase in the length of the intestinal villous and the number of related epithelium cells having been seen in the 400 ppm treatment group compared to the other studied treatment groups (p<0.05). By increasing the concentration of Mix-Oil, trout feed resistance has increased against oxidation. Although, the observed increments were only statistically significant in the 200 and 400 ppm Mix-Oil (p<0.05) compared to 50 ppm and control groups. The results suggested that dietary administration of Mix-Oil at the level of 400 ppm could improve growth performance of rainbow trout as well as increase the feed stability.