Department of Zoology, University of Johannesburg, Johannesburg, Gauteng, South Africa.
PLoS One. 2018 Jun 13;13(6):e0197804. doi: 10.1371/journal.pone.0197804. eCollection 2018.
Parasites of fishes have been shown to be effective bioindicators of the aquatic environment. Few investigations have been conducted on ectoparasite models and therefore little is known about the fate of trace elements and metals which they accumulate. In this study trace element sequestration was observed in the carapace of the fish louse, Argulus japonicus and found to relate to the sex of the parasite, as well as, the degree of sclerotization of the carapace. Adults of A. japonicus were collected from cyprinid hosts in the Vaal Dam, South Africa. Parasites were removed and flash frozen in liquid nitrogen before being sectioned with a cryomicrotome. Sections and whole mounts of parasites were prepared and treated with Phen-Green TM FL cell-permeant diacetate. Cryosections were assessed for trace elements and metals using a scanning electron microscope equipped with energy dispersive spectroscopy. Results indicated that in both male and female parasites, trace elements become bound to the carapace and produce more intense fluorescence than in soft tissues. Sexual dimorphic differences were further observed between male and female parasites. The intensity of the fluorescence signals was greater in the carapace of male parasites than in females, particularly when comparing the carapace of the ventral side of the thorax. In females, an amorphous layer of material surrounding the eggs was observed and produced an intense fluorescent signal. Levels of trace elements and metals detected were not significantly different between male and female parasites. Results observed serve as a demonstration for the first time of trace element sequestration in a freshwater crustacean parasite and possible mechanisms employed to reduce body burdens of trace elements and metals.
鱼类寄生虫已被证明是水生环境的有效生物指示剂。对外部寄生虫模型进行的研究很少，因此，对于它们积累的痕量元素和金属的命运知之甚少。在这项研究中，观察到鱼类虱子（Argulus japonicus）的甲壳中痕量元素的螯合作用，发现其与寄生虫的性别以及甲壳的硬化程度有关。从南非瓦尔大坝的鲤科鱼类宿主中收集了日本鱼虱的成虫。寄生虫被取出并在液氮中迅速冷冻，然后用 cryomicrotome 切片。制备了寄生虫的切片和全载玻片，并使用 Phen-Green TM FL 细胞可渗透二乙酸盐进行处理。使用配备能量色散光谱仪的扫描电子显微镜评估冷冻切片中的痕量元素和金属。结果表明，在雄性和雌性寄生虫中，痕量元素与甲壳结合，并产生比软组织更强烈的荧光。在雄性和雌性寄生虫之间还观察到了性二态性差异。雄性寄生虫甲壳的荧光信号强度大于雌性，尤其是在比较胸腹部的甲壳时。在雌性中，观察到围绕卵子的无定形物质层，并产生强烈的荧光信号。在雄性和雌性寄生虫之间检测到的痕量元素和金属水平没有显着差异。观察到的结果首次证明了淡水甲壳类寄生虫中痕量元素的螯合作用，以及可能用于减少痕量元素和金属体负荷的机制。
