Laboratory of Fish Protistology

Our main interests are eukaryotic microorganisms infecting fish, amphibians and reptiles, including all aspects of their structure, biology, physiology, life cycles, host-parasite interactions, ecology and especially their phylogeny and evolution. Our main focus are the Myxozoa, extremely reduced fish parasites belonging to the Cnidaria, but we also study other interesting microparasites like e.g. amoebae, apicomplexans, microsporidians, ciliates or dinoflagellates. As part of our work we carry out research into a range of parasite problems which create economic and health consequences for the aquaculture industry, in collaboration with various academic and professional institutions worldwide.

Current research projects


Myxozoans are diverse group of cnidarian parasites, that have been morphologically highly reduced as an adaptation to parasitism and that have conquered a range of different aquatic habitats. Myxozoans have a complex life cycle involving a vertebrate (fish) and an invertebrate (bryozoan, polychaete or oligochaete) host and some species cause important losses in the aquaculture sector. We conduct a wide range of studies on myxozoans:

Biology, phylogeny and evolution

For historical reasons, current myxozoan taxonomy is based predominantly on the morphology and structure of the spores produced in the vertebrate (fish) host. However, phylogenetic relationships among the myxozoans based on different gene regions disagree with the traditional taxonomic classification: a number of myxosporeans with very similar spore morphology and belonging to the same genus were found to be phylogenetically distantly related, rendering most genera non-monophyletic. But how important is spore morphotype for the evolution of these highly reduced parasites? One of our principal aims is to investigate differences with regard to parasite development as well as life cycles and biology, in order to be able to understand why they cluster in different branches of the phylogenetic tree. This will allow us to identify the characters which shape myxosporean evolution and will lead to a better understanding of the broad diversity of modern species.


Unveiling unknown myxozoan diversity and origins by eDNA

Myxozoan spore in amongst other plankton organismsDue to their microscopic size, cryptic nature and their ability to switch between different invertebrate and vertebrate host groups, we know virtually nothing about the true diversity of the Myxozoa. However, transmission from host to host involves the release of durable spore stages in the environment. Following marker design for different myxozoan lineages, we are currently analysing eDNA sequences generated by next generation sequencing of marine and freshwater filtrates and sediments from aquatic habitats around the world. Using this approach we have already discovered new phylogenetic lineages, which allow new insights into myxozoan evolution and may even clarify the question of a marine vs freshwater origin of the Myxozoa. Using molecular techniques, we furthermore investigate new host groups by analysing vertebrate and invertebrate taxa that have escaped our attention as potential myxozoan hosts to date. 


Repatriation of the Rhine with the Allis shad as an opportunity for parasite diversity

The anadromous fish species Alosa alosa (L.) was repatriated in the Rhine after approx. 70 years. We compared myxozoan infections in the Garonne/Dordogne river systems, where the shad is present in stable populations and in the Rhine where the first fish returned to spawn in 2014 after the reintroduction of young-of-the-year, 6 years before. The diversity of SSU rDNA clones of Hoferellus alosae was up to four times higher in the Rhine than in the French rivers and the genetic signature between individuals varied strongly. Our data demonstrate that the de novo establishment of myxozoan infections in rivers is slow but of great genetic diversity, which can only be explained by the introduction of spores from genetically diverse sources, predominantly via straying fish hosts. Long-term studies will show if and how the high diversity of a de novo introduction of host-specific myxozoans succeeds into the establishment of a local successful strain.                                                     

Myxozoan host exploitation and immune evasion

macrophage (green) attachment to blood stage of the myxozoan Sphaerospora molnari (red)We use transcriptomics and proteomics in combination with in vitro experiments to better understand how myxozoan proliferative stages in carp blood are able to multiply rapidly in the host and to use resources effectively, while avoiding host immune defense mechanisms. Most of our present research focusses on Sphaerospora molnari, the agent of skin and gill sphaerosporosis in common carp. S. molnari uses highly derived cytoplasmic actin to generate a completely novel type of cellular motility, which is driven by the rapid formation and reabsorption of membrane folds, hence creating a non-directional and surface-independent tumbling movement. We prove the importance of this type of motility for evading the attachment and lysis by host immune cells. Apart from this motility, S. molnari uses a wide repertoire of proteolytic enzymes to survive and propagate in the host blood, some of which we are currently describing and characterising biochemically. In parallel, we explore the immunological reaction of carp to S. molnari.                                                                                                                


Apart from our main focus on myxozoans, we investigate a wide diversity of protists in aquatic environments and hosts, studying their distribution, host-parasite interaction, pathology, ecology as well as functional and evolutionary aspects. Here’s some of our recent and ongoing research:                                                                      

Research into pathogenic and amphizoic amoebae

Our latest research encompases studies on the pathological agents involved in recent outbreaks of amoebic gill disease (AGD) in Atlantic salmon in Northern Europe (Paramoeba perurans and other Paramoeba strains) and we are testing a variety of substances for their efficacy against P. perurans and their suitability as in-feed treatments against AGD. Most of this research is sponsored by the R&D department of Skretting Aquaculture Research Centre. We also screen for of a variety of pathogenic amoebae in water sources impacted by human actions, using molecular methods, and we have a unique, comprehensive culture collection of amphizoic amoebae from different aquatic habitats and hosts, with hundreds of different strains. Some of these have recently been documented here: "Illustrated Guide to Culture Collection of Free-living Amoebae“ by I. Dyková and M. Kostka (2013); Academia (Prague), 363 pages. Neuveden. ISBN 978-80-200-2176-2. Please contact us if you are interested in further research on any of these strains.                                                                     

Epicellular parasites

Different types of epicellular host-parasite complexesWe recently reviewed the modes of interactions, invasion mechanisms and metabolic adaptations of epicellular apicomplexans. These infect cold-blooded hosts and represent poorly studied groups of parasites when compared with apicomplexans from warm-blooded animals. Epicellular apicomplexans reside in a host-derived envelope that adopts diverse morphologies as these parasites likely rely on various modes of nutrient uptake. The host-parasite connection of epicellular apicomplexans is characterized by formation of the feeder organelle in cryptosporidians in contrast to stages that have adapted monopodial or spider-like morphologies in coccidians. Transcriptome analyses of the epicellular coccidian Goussia janae revealed that RON and AMA proteins probably represent crucial molecular tools for these parasites “on their way in”. These parasite possess enzymes implicated in most of the central carbon metabolism, resembling the versatile metabolic capabilities of the intracellular coccidian Toxoplasma gondii rather than the reduced ones of the epicellular Cryptosporidium spp. Phylogenetic analyses of rDNA data revealed that epicellular parasitism most probably evolved convergently as an adaptation to colonization of different cell types and tissues. 


Perkinsea infection and population declines in amphibians

Leptopelis sp.Amphibians are among the most threatened animal groups worldwide. Population declines and extinctions have been linked, in part, to emerging infectious diseases. One such emerging disease has been attributed to Perkinsea-like protists causing mass mortality events in the United States. Using molecular methods, we evaluated the diversity of Perkinsea parasites in livers sampled from a wide taxonomic collection of tadpoles from six countries across three continents. We discovered a previously unidentified, phylogenetically distinct infectious agent of tadpole livers present in a broad range of frogs from both, tropical and temperate sites and across all sampled continents. These data demonstrate the high prevalence and global distribution of this infectious agent, wich is closely realted to Perkinsus sp., a “marine” protist responsible for mass-mortality events in commercial shellfish populations.                                                                      


Biology Centre CAS
Institute of Parasitology
Branišovská 1160/31
370 05 České Budějovice

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