Wright Daniel William, Nowak Barbara, Oppedal Frode, Crosbie Phil, Stien Lars Helge, Dempster Tim
Sustainable Aquaculture Laboratory - Temperate and Tropical, School of BioSciences, Melbourne, Vic., Australia.
Institute of Marine Research, Matre Research Station, Matredal, Norway.
J Fish Dis. 2018 Sep;41(9):1403-1410. doi: 10.1111/jfd.12834. Epub 2018 Jun 25.
Freshwater bathing is one of the main treatment options available against amoebic gill disease (AGD) affecting multiple fish hosts in mariculture systems. Prevailing freshwater treatments are designed to be long enough to kill Neoparamoeba perurans, the ectoparasite causing AGD, which may select for freshwater tolerance. Here, we tested whether using shorter, sublethal freshwater treatment durations are a viable alternative to lethal ones for N. perurans (2-4 hr). Under in vitro conditions, gill-isolated N. perurans attached to plastic substrate in sea water lifted off after ≥2 min in freshwater, but survival was not impacted until 60 min. In an in vivo experiment, AGD-affected Atlantic salmon Salmo salar subjected daily to 30 min (sublethal to N. perurans) and 120 min (lethal to N. perurans) freshwater treatments for 6 days consistently reduced N. perurans cell numbers on gills (based on qPCR analysis) compared to daily 3 min freshwater or seawater treatments for 6 days. Our results suggest that targeting cell detachment rather than cell death with repeated freshwater treatments of shorter duration than typical baths could be used in AGD management. However, the consequences of modifying the intensity of freshwater treatment regimes on freshwater tolerance evolution in N. perurans populations require careful consideration.
淡水浴是对抗海水养殖系统中影响多种鱼类宿主的阿米巴鳃病（AGD）的主要治疗方法之一。现行的淡水治疗设计时长足以杀死引起AGD的体外寄生虫秘鲁新帕拉变形虫（Neoparamoeba perurans），这可能会选择出对淡水的耐受性。在此，我们测试了对于秘鲁新帕拉变形虫（2 - 4小时）而言，使用更短的亚致死淡水治疗时长是否是致死时长的可行替代方案。在体外条件下，分离自鳃部并附着于海水塑料基质上的秘鲁新帕拉变形虫在淡水中≥2分钟后脱离，但直到60分钟后其存活才受到影响。在一项体内实验中，与每天进行3分钟淡水或海水处理6天相比，每天对受AGD影响的大西洋鲑（Salmo salar）进行30分钟（对秘鲁新帕拉变形虫为亚致死）和120分钟（对秘鲁新帕拉变形虫为致死）的淡水处理，持续6天，能持续减少鳃上的秘鲁新帕拉变形虫细胞数量（基于qPCR分析）。我们的结果表明，在AGD管理中，可以采用比典型浴疗持续时间更短的重复淡水处理来针对细胞脱离而非细胞死亡。然而，改变淡水治疗方案强度对秘鲁新帕拉变形虫种群淡水耐受性进化的影响需要仔细考虑。
