Genetic relatedness provides support for a species complex of myxosporeans infecting the Indian major carp, Labeo rohita

Myxozoans are an economically important group of microscopic metazoan parasites of fish. The myxozoan species Thelohanellus filli infects commercially important freshwater fish both in wild and in cultured habitat. This parasite causes gill hemorrhagic disease and significant damage to the respiratory surface of the infected fish. In the present study, the 18S rDNA gene sequence of morphologically identified T. filli infecting the gill lamellae of the Indian major carp, Labeo rohita, was characterized. This revealed that we are actually dealing with a species complex containing T. bifurcata, T. jiroveci and T. seni. Phylogenetically, T. filli clustered with other myxozoan parasites, with the species most closely related to T. filli having 96 to 97% sequence similarity. The intraspecific variation demonstrated in this study points towards the importance of newer approaches to facilitate reassessment of taxa and detecting species complexes and cryptic species.

粘孢子虫是一群对鱼类经济具有重要意义的微小多细胞寄生虫。Thelohanellus filli 粘孢子虫物种感染了商业上重要的淡水鱼类，无论是在野生环境中还是在养殖环境中。这种寄生虫会导致感染鱼类的鳃出血病，并对受感染鱼类的呼吸表面造成重大损害。在本研究中，对形态学上识别出的感染印度大鲢（Labeo rohita）鳃小叶的 T. filli 的 18S 核糖体 DNA 基因序列进行了表征。这表明我们实际上正在处理一个包含 T. bifurcata、T. jiroveci 和 T. seni 的物种复合体。从系统发育学的角度来看，T. filli 与其他粘孢子虫寄生虫聚类，其中与 T. filli 最接近的物种具有 96% 到 97% 的序列相似性。本研究中展示的种内变异表明，新的方法对于促进对分类群的重新评估、检测物种复合体和隐秘物种具有重要意义。