Centre for Sustainable Tropical Fisheries and Aquaculture and the College of Science and Engineering, James Cook University, Townsville, Queensland 4811, Australia.
Australian Institute of Marine Science PMB No 3, Townsville, Queensland 4810, Australia; School of Life and Environmental Sciences, Deakin University, Geelong, VIC 3216, Australia.
Int J Parasitol. 2020 Sep;50(10-11):839-849. doi: 10.1016/j.ijpara.2020.03.017. Epub 2020 Jul 12.
This study quantified the effects of temperature on reproduction and maternal provisioning of the ectoparasite, Neobenedenia girellae (Platyhelminthes: Monogenea), a species known to cause detrimental impacts to aquaculture fishes in tropical and subtropical environments worldwide. At 20 and 25 °C, parasites exhibited relatively slower production of larger eggs that were energy-dense. In contrast, parasites at 30 °C attained sexual maturity faster, were reproductively active over a shorter period, grew to a smaller size and laid smaller, less energy-rich eggs at a faster rate. As such, parasites exhibited two distinct reproductive patterns in response to temperature: parasites at lower temperatures produced larger eggs with higher energy content, while those at the higher temperature had a higher rate of egg production. Larger eggs produced under cooler conditions were better provisioned with energetic reserves and important, membrane-bound lipids that would likely facilitate larval longevity and development success. This is commensurate with previous observations of epizootics of this parasite species in aquaculture systems during winter. Meanwhile, eggs produced at 30 °C contained higher proportions of saturated fatty acids compared with polyunsaturated fatty acids, likely reflecting metabolic regulation of cell membrane fluidity, which is necessary for larvae to survive warm conditions. This study demonstrates that fish ectoparasites have evolved substantial reproductive and metabolic flexibility to maximise infection success under variable environmental conditions.
本研究量化了温度对寄生在热带和亚热带环境中水产养殖鱼类的外寄生虫 Neobenedenia girellae（扁形动物：单殖吸虫目）的繁殖和母体营养供应的影响。在 20 和 25°C 时，寄生虫产生的较大卵子数量相对较少，但能量密度较高。相比之下，30°C 下的寄生虫性成熟更快，繁殖活跃期更短，体型更小，产卵速度更快，卵更小，能量含量更低。因此，寄生虫对温度表现出两种截然不同的繁殖模式：低温下产生的卵子较大，能量含量较高，而高温下的卵子产卵速度较快。在较冷条件下产生的较大卵子具有更高的能量储备和重要的膜结合脂质，这可能有助于幼虫的长寿和发育成功。这与先前在冬季水产养殖系统中观察到这种寄生虫的爆发相吻合。同时，在 30°C 下产生的卵子中，饱和脂肪酸的比例高于多不饱和脂肪酸，这可能反映了细胞膜流动性的代谢调节，这对于幼虫在温暖条件下的生存是必要的。本研究表明，鱼类外寄生虫已经进化出了相当大的繁殖和代谢灵活性，以在多变的环境条件下最大限度地提高感染成功率。
