This case represents the first documented report of aquatic oligochaetes (Pristina aequiseta) infesting fish. Oligochaetes are common and ubiquitous in aquatic environments, but parasitic (and symbiotic) species are extremely rare with a few species occurring in frogs. During a disease surveillance project, live oligochaetes were observed in fresh preparations of gills of the Australian freshwater Murray cod (Maccullochella peelii) that had been reared in a recirculating aquaculture system. Large numbers of oligochaetes were also found in detritus from the biofiltration system of the tanks. In autopsied fish, patches of filaments showed marked and diffuse hyperplasia, goblet cell metaplasia and mainly mononuclear infiltrate. This infestation may have caused sufficient damage to compromise the health of the fish and even death, considering that heightened mortality had occurred prior to their discovery. This infestation was considered not a case of parasitism but rather an opportunistic colonisation event triggered by a number of factors including the presence of a large population of P. aequiseta within the recirculating aquaculture system and unhealthy (or stressed) fish that could not ward off infestation.

此案是水生寡头鱼类（Pristina aequiseta）侵染鱼类的第一个文献报道。寡头类常见于水生环境中，但寄生（和共生）物种极为罕见，少数物种出现在青蛙中。在疾病监测项目中，在澳大利亚淡水鳕鱼（Maccullochellapeii）g的新鲜制剂中观察到了活寡头）在循环水产养殖系统中饲养。坦克的生物过滤系统的碎屑中也发现了大量的寡头类。在尸检鱼中，细丝斑块表现出明显的弥漫性增生，杯状细胞化生和主要为单核浸润。考虑到在发现之前已经增加了死亡率，这种侵扰可能已经造成了足够的损害，损害了鱼类的健康，甚至导致死亡。认为这种侵染不是寄生虫的情况，而是由许多因素触发的机会性定殖事件，包括循环水产养殖系统中大量马兜铃假单胞菌的存在以及无法抵御侵扰的不健康（或受压）鱼类。