Wongkaew Janchai, Chatchaiphan Satid, Taengphu Suwimon, Dong Ha Thanh, Senapin Saengchan, Piyapattanakorn Sanit
Program in Biotechnology, Faculty of Science, Chulalongkorn University, Bangkok, Thailand.
Department of Aquaculture, Faculty of Fisheries, Kasetsart University, Bangkok, Thailand.
J Fish Dis. 2025 Jul;48(7):e14113. doi: 10.1111/jfd.14113. Epub 2025 Mar 4.
Lactococcosis, primarily caused by Lactococcus garvieae, is prevalent in various freshwater fish species globally. Yet, its significance in Thai fish aquaculture remains poorly understood. This study investigated Lactococcosis-associated diseases across four red tilapia (Oreochromis sp.) and one Asian sea bass (Lates calcarifer) farm in Thailand in 2022. Chronically diseased fish displaying clinical signs such as exophthalmia or corneal opacity, erratic swimming, scale loss and skin haemorrhage, as well as apparently healthy specimens, were studied. Bacterial isolation was performed from the fish internal organs. Gram-positive bacterial isolates were selected and later identified as L. lactis (n = 4), L. taiwanensis (n = 1), L. garvieae (n = 2) and L. petauri (n = 2) based on bacterial 16S rDNA and gyrB partial sequences. Sub-adults of Nile tilapia were intracoelomic (IC) injected with representatives of each of the three Lactococcus species (L. garvieae, L. lactis and L. taiwanensis) at varying doses (10-10 CFU/fish), while juvenile Asian sea bass were IC injected with L. petauri at doses ranging from 10 to 10 CFU/fish. Control groups received culture medium alone. By the end of the 21-day test, mortality rates from all challenge groups ranged from 0% to 14.82%. Some clinical signs were observed in groups challenged with higher doses of the bacteria. Enzyme-linked immunosorbent assay (ELISA) showed that survivor fish exposed to high bacterial doses elicited specific antibodies IgM. In summary, this study identifies the presence of Lactococcus species in farmed fishes, which exhibit low virulence in Nile tilapia and Asian sea bass under laboratory-controlled challenges. These bacterial isolates appear to be opportunistic rather than pathogenic, potentially indicating underlying health challenges within the affected farms.
乳球菌病主要由格氏乳球菌引起，在全球各种淡水鱼品种中普遍存在。然而，其在泰国鱼类养殖中的重要性仍知之甚少。本研究于2022年对泰国四个红罗非鱼（奥利亚罗非鱼属）养殖场和一个尖吻鲈养殖场中与乳球菌病相关的疾病进行了调查。研究了表现出眼球突出或角膜混浊、游动异常、鳞片脱落和皮肤出血等临床症状的慢性患病鱼以及看似健康的样本。从鱼的内脏进行细菌分离。选择革兰氏阳性细菌分离株，随后根据细菌16S rDNA和gyrB部分序列鉴定为乳酸乳球菌（n = 4）、台湾乳球菌（n = 1）、格氏乳球菌（n = 2）和佩氏乳球菌（n = 2）。尼罗罗非鱼亚成体通过体腔注射三种乳球菌（格氏乳球菌、乳酸乳球菌和台湾乳球菌）的代表菌，剂量各不相同（10⁴ - 10⁸ CFU/鱼），而亚洲尖吻鲈幼鱼通过体腔注射佩氏乳球菌，剂量范围为10⁴ - 10⁸ CFU/鱼。对照组仅接受培养基。到21天试验结束时，所有攻毒组的死亡率在0%至14.82%之间。在用较高剂量细菌攻毒的组中观察到了一些临床症状。酶联免疫吸附测定（ELISA）表明，暴露于高细菌剂量的存活鱼产生了特异性抗体IgM。总之，本研究确定了养殖鱼类中存在乳球菌，在实验室控制的攻毒条件下，这些菌在尼罗罗非鱼和亚洲尖吻鲈中表现出低毒力。这些细菌分离株似乎是机会致病菌而非病原菌，这可能表明受影响养殖场存在潜在的健康问题。
