Cymbopogon flexuosus essential oil as an additive improves growth, biochemical and physiological responses and survival against Aeromonas hydrophila infection in Nile tilapia

Abstract The objective of the present study was to evaluate growth, biochemical, hematological and intestinal enzymes responses and survival of Nile tilapia juveniles fed a diet containing the essential oil of lemongrass Cymbopogum flexuosus (EOCF) and infected by Aeromonas hydrophila. Five diets were evaluated (in quadruplicate) with increasing levels of EOCF (0.0 - control; 0.25; 0.50; 1.0 and 2.0 mL kg diet-1). On day 45, eight fish per treatment were sampled and blood, liver and intestine samples were taken. Others eight fish per treatment were infected with A. hydrophila followed by a 15-day period of observation. Citral is the main constituent of EOCF. The inclusion of 2.0 mL EOCF kg diet-1 increased specific growth rate and survival after A. hydrophila infection and decreased feed conversion ratio of Nile tilapia. In general, higher concentrations of EOCF in the diet reduced plasma glucose and triglycerides levels, and increased plasma amino acids, alanine aminotransferase (ALT) and hepatic ALT levels, hematological parameters, and the activity of intestinal enzymes. It was concluded that the inclusion of 2.0 mL EOCF kg diet-1 improved growth performance, biochemical and physiological responses and decreased mortality of Nile tilapia after A. hydrophila infection.

摘要 本研究旨在评估投喂添加柠檬草（Cymbopogon flexuosus）精油（EOCF）的饲料后，感染嗜水气单胞菌（Aeromonas hydrophila）的尼罗罗非鱼（Nile tilapia）幼鱼的生长、生化、血液学及肠道酶响应与存活情况。本实验设置5组饲料（每组设4个重复），添加梯度浓度的EOCF（0.0 mL·kg⁻¹饲料为对照组；0.25、0.50、1.0及2.0 mL·kg⁻¹饲料）。实验第45天时，每组采集8尾鱼，采集血液、肝脏及肠道样本；另每组取8尾鱼感染嗜水气单胞菌，随后开展为期15天的观察。EOCF的主要成分为柠檬醛。投喂添加2.0 mL·kg⁻¹饲料EOCF的饲料，可提升尼罗罗非鱼的特定生长率及嗜水气单胞菌感染后的存活率，并降低饲料系数。总体而言，饲料中EOCF浓度越高，血浆葡萄糖与甘油三酯水平越低，而血浆氨基酸、丙氨酸氨基转移酶（alanine aminotransferase，ALT）及肝脏ALT水平、血液学参数与肠道酶活性均有所升高。综上，在饲料中添加2.0 mL·kg⁻¹饲料的EOCF，可改善尼罗罗非鱼的生长性能、生化与生理响应，并降低嗜水气单胞菌感染后的死亡率。