In the present study, the effect of Dracocephalum kotschyi essential oil (DKE) was investigated on growth, haematology, immune and antioxidant defence system and resistance of rainbow trout juveniles to bacterial infection (Aeromonas hydrophila). For this purpose, the fish were fed a diet containing different concentrations of DKE including 0 (control), 0.2, 0.25 and 0.3 mg/kg diet in three replicates for 60 days. After feeding trial, the fish were challenged with a pathogenic dose of A. hydrophila. Based on the results, immune components in plasma (alternative complement activity [ACH₅₀], IgM content, lysozyme activity, total protein and total albumin) and mucus (protease activity, IgM content and lysozyme activity) significantly elevated in fish fed diet containing 0.2 and 0.25 mg DKE/kg diet compared with other groups (p < 0.01). The plasma bactericidal activity increased in all DKE-supplemented fish. Supplementation of fish with 0.3 mg DKE/kg diet depressed the mucosal lysozyme activity and IgM content. The liver antioxidant enzymes, glutathione peroxidase (GPx), catalase (CAT) and superoxide dismutase (SOD) showed increased activity in response to 0.25 and 0.3 mg DKE/kg diet compared with other experimental diets (p < 0.01). Dietary DKE changed the haematology of the fish. The haematocrit, red blood cell count (RBC), white blood cell (WBC), haemoglobin content and mean erythrocyte cell haemoglobin content (MCHC) increased in response to DKE. In contrast, the mean corpuscular haemoglobin (MCH) decreased in fish fed 0.2 and 0.25 mg DKE/kg diet compared with other diets (p < 0.01). The supplementation of fish with 0.2 and 0.25 mg DKE/kg diet decreased the expression of cytokine-related genes, TNF-α and IL-8. In contrast, the DKE up-regulated the expression of the immune-related genes, C3 and lysozyme. DKE at concentration of 0.3 mg/kg diet depressed the C3 and lysozyme gene expressions. The DKE supplementation decreased the mortality rate of the fish after bacterial challenge compared with non-supplemented ones (p < 0.01). In conclusion, the findings of this study revealed the immune-stimulating effects of DKE at optimized dietary concentrations. In addition, DKE decreased the mortality induced by A. hydrophila infection.

中文翻译：

---

膳食 Dracocephalum kotschyi 精油改善了虹鳟鱼 (Oncorhynchus mykiss) 的生长、血液学、免疫力和对嗜水气单胞菌的抵抗力

在本研究中，研究了葛花龙头精油 (DKE) 对虹鳟幼鱼 (嗜水气单胞菌) 生长、血液学、免疫和抗氧化防御系统以及对细菌感染 (嗜水气单胞菌) 的抵抗力的影响。为此，给鱼喂食含有不同浓度 DKE 的饮食，包括 0（对照）、0.2、0.25 和 0.3 mg/kg 饮食，重复 3 次，持续 60 天。喂食试验后，用致病剂量的A.hydrophila攻击鱼。根据结果​​，血浆中的免疫成分（替代补体活性 [ACH ₅₀]，与其他组相比，含 0.2 和 0.25 mg DKE/kg 日粮的鱼饲料中的 IgM 含量、溶菌酶活性、总蛋白和总白蛋白）和粘液（蛋白酶活性、IgM 含量和溶菌酶活性）显着升高（p  < 0.01） . 所有添加了 DKE 的鱼的血浆杀菌活性都增加了。用 0.3 mg DKE/kg 饮食补充鱼可抑制粘膜溶菌酶活性和 IgM 含量。肝脏抗氧化酶、谷胱甘肽过氧化物酶 (GPx)、过氧化氢酶 (CAT) 和超氧化物歧化酶 (SOD) 与其他实验日粮相比，在 0.25 和 0.3 mg DKE/kg 日粮中表现出更高的活性（p < 0.01)。膳食 DKE 改变了鱼的血液学。血细胞比容、红细胞计数 (RBC)、白细胞 (WBC)、血红蛋白含量和平均红细胞血红蛋白含量 (MCHC) 响应 DKE 增加。相比之下，与其他日粮相比，饲喂 0.2 和 0.25 mg DKE/kg 日粮的鱼的平均红细胞血红蛋白（MCH）降低（p  < 0.01）。鱼补充 0.2 和 0.25 mg DKE/kg 日粮降低了细胞因子相关基因 TNF-α 和 IL-8 的表达。相比之下，DKE 上调了免疫相关基因 C3 和溶菌酶的表达。浓度为 0.3 mg/kg 饮食的 DKE 抑制了 C3 和溶菌酶基因的表达。与未添加 DKE 相比，添加 DKE 降低了细菌攻击后鱼的死亡率（p  < 0.01)。总之，本研究的结果揭示了 DKE 在优化膳食浓度下的免疫刺激作用。此外，DKE 降低了由A. hydrophila感染引起的死亡率。