Coccidian parasites of fish encompass profound phylogenetic diversity and gave rise to each of the major parasitic groups in terrestrial vertebrates

Abstract

Fish are the oldest and most diverse group of vertebrates; it therefore stands to reason that fish may have been the original hosts for many types of extant vertebrate parasites. Here, we sought to determine whether coccidian parasites of fish are especially diverse. We therefore sampled such parasites from thirty-nine species of fish and tested phylogenetic hypotheses concerning their relationships, using 18S rDNA. We found compelling phylogenetic support for distinctions among at least four lineages of piscine parasites presently ascribed to the genus Goussia. Some, but not all parasites attributed to Eimeria were confirmed as such. Major taxonomic revisions are likely justified for these parasites of fish, which appear to have given rise to each of the major lineages of coccidian parasites that subsequently proliferated in terrestrial vertebrates, including those such as Toxoplasma gondii that form tissue cysts in intermediate hosts.

Epicellular coccidiosis in goldfish

“…Recent phylo genetic works (Molnár et al 2012, Rosenthal et al 2016) have validated deep evolutionary distinctions among the coccidian parasites of fish, including (but not limited to) a monophyletic assemblage restricted to true members of the genus Eimeria. Subdivisions within Goussia correspond to morphological and developmental attributes that likely warrant further taxonomic revision.…”

“…Among Goussia spp. collected from Hungarian fishes, Rosenthal et al (2016) found that molecular sequences of species with small dispersed oocysts developing in the gut of their hosts throughout the year differ from those of species with large oocysts developing seasonally in nodules and epicellular sites. Large differences were also found between nodular and epicellular species.…”

“…Several authors, among them Upton (2000) and Duszynski et al (2016), still regard Goussia as a synonym of Eimeria. In recent studies (Molnár et al 2012, Rosenthal et al 2016) examining molecular sequences of different fish coccidia, however, great differences among Eimeria and Goussia spp. were documented, and at least 4 groups can be clearly differentiated within the members of Goussia.…”

“…On the other hand, the large differences in morphology, development and molecular sequences between the epicellularly developing coccidia of Goussia and the type specimen Epieimeria anguillae indicate a lack of relationship between the 2 eimerian groups. Differences in the development (permanently developing group versus annually developing groups) and intracellular location (intracytoplasmal and epicytoplasmal), and also differences in the molecular sequences among dispersed, nodularly and epicellularly developing groups (Rosenthal et al 2016) would favour the creation of new coccidian genera in the future, among them a genus with the tentative name Epigoussia.Ethical approval. All applicable institutional, natio nal and international guidelines for the care and use of animals were followed.…”

Fussing about fission: defining variety among mainstream and exotic apicomplexan cell division modes

“…Goussia spp. are found in fish, reptiles and amphibians, which have not been extensively studied 812 at the cell biological level (Rosenthal et al, 2016). Overall, why the two different extant forms of 813 budding exist cannot be answered with satisfaction based on the factors we considered.…”