Scientists used genome reconstruction to identify a previously unseen fish parasite found in many marine fish species worldwide. Part of a critical group of clinical parasites called apicomplexans, the parasite had been overlooked in previous studies. Its presence is widespread among different fish species both geographically and globally, and has significant impacts on commercial fisheries and marine food chains.

An international team of scientists from the Rosenstiel School of Marine, Atmospheric and Earth Sciences at the University of Miami and the Institute for Evolutionary Biology (IBE), a joint center of the Spanish National Research Council (CSIC) and Pompeu Fabra University (UPF)), discovered a tropical discovered a new parasite in the red-lipped belna, a reef fish. This study also revealed the global distribution of this parasite in fish populations worldwide.

In a published study Current Biologyused an innovative method to reconstruct part of the parasite’s genome based on sequence data obtained from the host and detect its presence in other fish using genetic “barcodes” (DNA barcoding).

An “invisible” parasite has been discovered

Despite being found in fish worldwide, the parasite has not been fully identified until now. Genomic data from the study suggests that the parasite belongs to a previously unidentified group of organisms called ichthyocolids, which is Latin for “fish-dwelling.”

“Although previously identified by microscopy, we have so far not succeeded in separating the genomic signal from the fish host and the parasite. For the first time, we were able to identify them using their DNA and assign them to a well-known group of apicomplexan parasites,” said study leader and co-author of the IBE’s Microbial Ecology and Evolution Principal Investigator Javier del Campo. group and at the Rosenstiel School in Miami.

The parasite is present in fish all over the world

In addition to identifying an entirely new group of Apicomplexans, reconstructing the genome allowed the researchers to identify a set of genes that could be used to detect the presence of this organism in other samples of the genome or microbiome, as if it were a “barcode”.

“When we found ichthyocollites in the redlip, a tropical fish, we wondered whether they might be part of the microbiota of other fish,” says Anthony Bonacolta, a PhD in marine biology and ecology at the Rosenstiel School and first author of this book. study.

The team compared the DNA of these apicomplexans with publicly available microbiome databases of hundreds of freshwater and marine fish species. The results showed that these parasites are associated with most of the marine fish species analyzed and are present in all oceans. Therefore, they would be one of the most common parasites among marine fish, with potential impacts on commercial fisheries and ocean food webs.

“Future research may help us better understand the impact of parasites such as ichthyocollites that dominate marine ecosystems,” Del Campo says.

A new member of the apicomplexan parasites

Ichthiocolitis belongs to the Apicomplexa, a large group of parasites that includes those that cause malaria and toxoplasmosis. However, these parasites do not pose a direct risk to human health, but it is important to study them for the health of ocean ecosystems and obtain more information about the evolution of these human parasites.

The discovery of ichthyocolids adds further context to this evolution. For the first time, they are placed as a sister group to corallicolids, well-known coral dwellers that have recently been described as apicomplexans.

“Studying ichthyocolides not only reveals more about the evolution of the host parasites, but also reveals other key features of apicomplexans that may be clinically important. They may use similar infection mechanisms (since they are also blood parasites) or have similar biology that could inform our understanding of other apicomplexans.” they could be,” Bonacolta said.