Mizuno Shinya, Urawa Shigehiko, Miyamoto Mahito, Hatakeyama Makoto, Sasaki Yoshitaka, Koide Nobuhisa, Tada Shoichi, Ueda Hiroshi
Salmon and Freshwater Fisheries Research Institute, Hokkaido Research Organization, Eniwa, Japan.
Hokkaido National Fisheries Research Institute, Japan Fisheries Research and Education Agency, Sapporo, Japan.
J Fish Biol. 2018 Sep;93(3):528-539. doi: 10.1111/jfb.13681.
The present study performed three experiments to establish a practical prevention strategy for the ectoparasitic flagellate Ichthyobodo salmonis and ciliate Trichodina truttae in hatchery-reared juvenile chum salmon Oncorhynchus keta using dietary supplementation with oregano essential oil. Experiment 1 showed that a diet supplemented for 3 weeks with 0.02% oregano essential oil significantly prevented infection with I. salmonis and T. truttae in juveniles reared in small tanks. Experiment 2, in outdoor hatchery ponds, demonstrated that the oregano treatment completely prevented I. salmonis infection for 52 days and T. truttae infection for 38 days. Oregano-treated juvenile mortality attributable to infection with these protozoans also decreased to 7.6% of control juvenile mortality, confirming the utility of this treatment in cultured O. keta. Physiological analyses of the oregano-treated juveniles elucidated the treatment's safety in relation to their metabolism, osmoregulation, natural immunity and olfactory responses and also detected carvacrol (a major component of oregano essential oil which shows antimicrobial activity) on the skin. In experiment 3, exposure of the two protozoans to oregano essential oil revealed a weak antiparasitic action on the body surface of the juvenile O. keta. The overall results demonstrate that dietary oregano supplementation is a practical prevention strategy for I. salmonis and T. truttae in hatchery-reared juvenile O. keta and suggest the possibility that its anti-parasitic action is attributable to a component of the oil that emerges onto the skin of the body of the fish.
本研究进行了三项实验，以建立一种实用的预防策略，用于防治孵化场养殖的大麻哈鱼幼鱼（Oncorhynchus keta）身上的体外寄生鞭毛虫鲑居尾孢虫（Ichthyobodo salmonis）和纤毛虫鲟车轮虫（Trichodina truttae），方法是在饲料中添加牛至精油。实验1表明，在小型水箱中饲养的幼鱼饲料中添加0.02%牛至精油3周，可显著预防鲑居尾孢虫和鲟车轮虫感染。实验2在室外孵化场池塘进行，结果表明牛至处理可在52天内完全预防鲑居尾孢虫感染，在38天内预防鲟车轮虫感染。经牛至处理的幼鱼因这些原生动物感染导致的死亡率也降至对照幼鱼死亡率的7.6%，证实了该处理方法在养殖大麻哈鱼中的有效性。对经牛至处理的幼鱼进行的生理分析阐明了该处理方法在代谢、渗透压调节、天然免疫和嗅觉反应方面的安全性，还在鱼皮肤上检测到了香芹酚（牛至精油的主要成分，具有抗菌活性）。在实验3中，将这两种原生动物暴露于牛至精油中，结果显示对大麻哈鱼幼鱼体表有微弱的抗寄生虫作用。总体结果表明，在饲料中添加牛至是防治孵化场养殖的大麻哈鱼幼鱼感染鲑居尾孢虫和鲟车轮虫的一种实用预防策略，并表明其抗寄生虫作用可能归因于牛至精油中一种出现在鱼体皮肤上的成分。
