Dietary effect of Ziziphora clinopodioides extract on zootechnical performance, immune response, and disease resistance against Yersinia ruckeri in Oncorhynchus mykiss

Abstract An eight-week feeding experiment was performed to determine the potential effects of Blue Mint Bush, Ziziphora clinopodioides, extract (ZE) on growth, digestive enzymes activity, immune response (serum and mucus), and disease resistance in rainbow trout. Accordingly, 450 fish (21.19 ± 1.09 g) were divided into five groups and fed with the experimental diets including: ZE 0% (control diet), ZE 0.5 %, ZE 1.5 %, ZE 3% and ZE 4.5 %. The administration of ZE, except ZE 0.5 %, significantly increased weight gain and specific growth rate compared to the control group (p 0.05). The highest survival rate (56 %) was recorded in the fish fed with ZE 3 % when the fish were exposed to Yersinia ruckeri on 15 days. Collectively, our results demonstrated that ZE-enriched diets, especially at the level of 3 %, supported growth performance, digestive enzyme activity, non-specific immune system, and resistance to Y. ruckeri infection in fry rainbow trout.