Francisellosis is a disease responsible for severe economic losses in aquaculture. Currently, this disease is controlled via biosecurity measures and treatment of affected batches. In this study, tilapia juveniles were challenged with Francisella orientalis via immersion and fed with oxytetracycline-medicated feed, at 100 mg kg fish⁻¹ and 200 mg kg fish⁻¹, under prophylactic and therapeutic strategies for 16 and 15 days respectively. All doses and treatment strategies reduced the fish mortality. The detection of the pathogen from the spleen was lower in the treated groups. Histopathology analysis showed that challenged fish that received the highest dosage presented fewer granuloma in their spleens and less inflammatory infiltrate in their livers than untreated fish. Fish that received the prophylactic treatment, regardless of the dose, presented fewer granuloma in their livers than untreated fish. Fish treated with 100 mg kg fish⁻¹ had better scores for hepatocyte accumulations than fish treated with the higher dosage. Furthermore, 20% of the unchallenged fish that received the higher dosage presented mild inflammatory infiltrate in their livers. No differences were observed in the serum hepatocyte lesion enzyme quantifications. The results indicate that oxytetracycline-medicated feed is safe, even at the higher dose, and effective at controlling francisellosis in tilapia.

中文翻译：

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施用脱水土霉素可有效降低尼罗罗非鱼的紫蛉病死亡率

弗朗西斯氏菌病是一种导致水产养殖严重经济损失的疾病。目前，这种疾病是通过生物安全措施和受影响批次的治疗来控制的。在这项研究中，罗非鱼幼鱼通过浸入方式用东方弗朗西斯菌进行攻击，并用含土霉素的饲料喂养，分别为 100 mg kg 鱼^-1和 200 mg kg 鱼^-1，分别在 16 天和 15 天的预防和治疗策略下。所有剂量和治疗策略都降低了鱼的死亡率。治疗组从脾中检出病原体较低。组织病理学分析表明，与未经处理的鱼相比，接受最高剂量攻击的鱼脾脏中的肉芽肿较少，肝脏中的炎症浸润较少。接受预防性治疗的鱼，无论剂量如何，肝脏中的肉芽肿都比未治疗的鱼少。用 100 mg kg 鱼处理的鱼⁻¹与用较高剂量处理的鱼相比，肝细胞积累的分数更高。此外，接受较高剂量的未受攻击的鱼中有 20% 的肝脏出现轻度炎症浸润。在血清肝细胞损伤酶定量中没有观察到差异。结果表明，添加土霉素的饲料即使在较高剂量下也是安全的，并且可有效控制罗非鱼的紫蛉病。