Nilton Lins University, Av. Nilton Lins, 3269, 69058-030, Manaus, AM, Brazil.
Federal University of Amazonas, Av. General Rodrigo Octavio Jordão Ramos, 1200, 69067-005, Manaus, AM, Brazil.
Vet Parasitol. 2022 Mar;303:109667. doi: 10.1016/j.vetpar.2022.109667. Epub 2022 Feb 1.
Trichodinids are problematic ectoparasites for intensive arapaima fish farming, which can make their breeding costly and unprofitable. The search for effective and safe therapeutic molecules is constant, and chloramine-T has stood out as an effective biocide to treat various pathogens in aquaculture. Here we investigated the acute toxicity (LC) of chloramine-T and its behavioural, morphological, histological, physiological, and antiparasitic effects on the control of trichodinids in arapaima juveniles. Initially arapaima were exposed to chloramine-T (0, 10, 20, 40, 50, 60, 80, 100 mg L) for 4 h. During this period, behavioural, morphological, and mortality changes were recorded. Immediately after a toxicity test, gills were collected for the histological analysis. The LC was calculated at 23.8 mg L of chloramine-T. Behavioural changes like erratic swimming, loss of balance, gasping at the water surface, excessive mucus, jumping at the water surface, lethargy and gill hyperventilation, and morphological changes like loss of scales, ocular opacity, and skin darkening, were considered mild in arapaima exposed to 10 and 20 mg L of chloramine-T for 4 h. The arapaima gills exposed to 10, 20 and, 40 mg L of chloramine-T presented epithelial hyperplasia, dilated venous sinus and eosinophilic infiltrate, but they were reversible and of a low pathological degree. Based on the acute toxicity test (LC) results, concentrations were defined for the in vivo efficacy test, during which arapaima were exposed to 0, 10, 15, and 20 mg L of chloramine-T for 1 h. After a therapeutic bath, physiological and parasitological analyses were performed. The use of 20 mg L of chloramine-T significantly reduced (p < 0.05) parasitism by Trichodina sp. with an efficacy of 50.27 % and 53.23 % in gills and on the body surface, respectively. Chloramine-T did not change haematological parameters (erythrogram and thrombogram) or the biochemical parameters of arapaima after 1 h of exposure. However, monocytosis and neutrophilia were noted at slightly higher concentrations (15 and 20 mg L), but changes in fish homeostasis were not characterised. Thus, we demonstrate that the application of a therapeutic bath with 20 mg L of chloramine-T for 1 h reduces parasitism by trichodinids and does not affect general arapaima juvenile health.
纤毛虫是集约化养殖巨骨舌鱼的一种有问题的外寄生虫，会使养殖成本变得昂贵且无利可图。寻找有效且安全的治疗性分子是持续的，氯胺-T 已被证明是一种有效的杀菌剂，可用于治疗水产养殖中的各种病原体。在这里，我们研究了氯胺-T 的急性毒性 (LC) 及其对控制巨骨舌鱼幼鱼纤毛虫的行为、形态、组织学、生理学和抗寄生虫作用。最初，巨骨舌鱼暴露于氯胺-T（0、10、20、40、50、60、80、100mg/L）4 小时。在此期间，记录了行为、形态和死亡率的变化。毒性试验后立即采集鳃用于组织学分析。氯胺-T 的 LC 计算为 23.8mg/L。在暴露于 10 和 20mg/L 氯胺-T 的 4 小时内，巨骨舌鱼出现行为异常、失去平衡、在水面喘息、过度分泌黏液、在水面跳跃、昏睡和鳃过度通气、鳞片脱落、眼睛混浊和皮肤变黑等形态变化，被认为是轻度的。暴露于 10、20 和 40mg/L 氯胺-T 的巨骨舌鱼的鳃上皮增生、静脉窦扩张和嗜酸性浸润，但这些变化是可逆的，病理程度较低。基于急性毒性试验（LC）结果，确定了体内疗效试验的浓度，在此期间，巨骨舌鱼暴露于 0、10、15 和 20mg/L 的氯胺-T 1 小时。治疗浴后，进行生理和寄生虫学分析。使用 20mg/L 的氯胺-T 可显著降低（p<0.05） Trichodina sp. 的寄生率，在鳃和体表上的疗效分别为 50.27%和 53.23%。暴露于 1 小时后，氯胺-T 不会改变巨骨舌鱼的血液学参数（红细胞和血小板）或生化参数。然而，在稍高的浓度（15 和 20mg/L）下观察到单核细胞增多症和嗜中性粒细胞增多症，但鱼类体内平衡的变化没有特征。因此，我们证明应用 20mg/L 的氯胺-T 治疗浴 1 小时可降低纤毛虫的寄生率，且不会影响巨骨舌鱼幼鱼的整体健康。
