Department of Veterinary Medicine, School of Animal Husbandry and Food Engineering, São Paulo University - FZEA/USP, Pirassununga, SP, Brazil.
Department of Ecology and Evolutionary Biology, Federal University of São Paulo - UNIFESP, Diadema, SP, Brazil; Department of Animal Biology, Institute of Biology, State University of Campinas - UNICAMP, Campinas, SP, Brazil.
Microb Pathog. 2022 Jan;162:105370. doi: 10.1016/j.micpath.2021.105370. Epub 2021 Dec 23.
Although species of the genus Ceratomyxa Thélohan, 1892 mostly parasitize marine fish around the world, a surprising diversity of the genus has recently been reported from Amazonian freshwater fish. In this study, we report a freshwater Ceratomyxa species parasitizing Hemiodus orthonops (Hemiodontidae) from the Paraná River (La Plata Basin) in a watershed flowing into the southern part of South America, which expands the geographic distribution of this fish parasite in the freshwater resources of the continent. We applied a combination of morphological, small subunit ribosomal DNA (SSU rDNA), and phylogenetic analyses, and vermiform-shaped plasmodia endowed with motility were found swimming in the bile of the fish. The characteristics of the plasmodia and myxospores of the Ceratomyxa species found in the Paraná River resembled those of Ceratomyxa fonsecai, a parasite of the congeneric host Hemiodus unimaculatus from the Tocantins River basin in northern Brazil. Due to the close morphological and morphometric resemblances and the impossibility of genetic comparison, the parasite found in H. orthonops from the Paraná River was designated as Ceratomyxa cf. fonsecai, and the definition of its taxonomic status was left for further study. Maximum likelihood and Bayesian analyses showed Ceratomyxa cf. fonsecai clustering within a well-supported clade, together with other Amazonian freshwater ceratomyxids. The present study suggests that shifts of the complex host/parasite between marine and freshwater environments were facilitated by marine incursions into South America in the Early Miocene.
虽然属 Ceratomyxa Thélohan, 1892 的物种主要寄生在世界各地的海洋鱼类中，但最近在亚马逊淡水鱼中报道了该属的惊人多样性。在这项研究中，我们报告了一种寄生在 Hemiodus orthonops（Hemiodontidae）的淡水 Ceratomyxa 物种，该物种来自拉普拉塔盆地的巴拉那河（南美洲南部的一个流域），这扩展了这种鱼类寄生虫在该大陆淡水资源中的地理分布。我们应用了形态学、小亚基核糖体 DNA（SSU rDNA）和系统发育分析的组合，发现具有运动能力的蠕虫状原生质体在鱼的胆汁中游动。在巴拉那河中发现的 Ceratomyxa 物种的原生质体和粘孢子的特征与 Ceratomyxa fonsecai 相似，后者是巴西北部托坎廷斯河流域同种宿主 Hemiodus unimaculatus 的寄生虫。由于形态和形态测量上的密切相似性以及遗传比较的不可能，在巴拉那河中发现的 H. orthonops 的寄生虫被指定为 Ceratomyxa cf. fonsecai，其分类地位的定义留待进一步研究。最大似然和贝叶斯分析表明，Ceratomyxa cf. fonsecai 与其他亚马逊淡水 Ceratomyxidae 一起聚类在一个支持良好的分支中。本研究表明，海洋入侵到南美洲的中新世促成了复杂的宿主/寄生虫在海洋和淡水环境之间的转移。
