USA – Researchers have uncovered a previously undetected parasite present in numerous marine fish species worldwide, using innovative genome reconstruction techniques.

This significant discovery was made by a team from the University of Miami Rosenstiel School of Marine, Atmospheric, and Earth Science, in collaboration with the Institute of Evolutionary Biology (IBE) in Spain.

The parasite, belonging to the apicomplexans group, has historically gone unnoticed in marine fish studies.

Apicomplexans include some of the most clinically important parasites, such as those causing malaria and toxoplasmosis. This new parasite, now named ichthyocolids, comes from the Latin term meaning “fish dweller.” The discovery was published in the journal Current Biology.

Genome reconstruction

Using an innovative method to reconstruct part of the parasite’s genome from sequencing data obtained from its host, researchers were able to detect the parasite’s presence in various fish species.

This method used genetic “barcodes” to identify the parasite’s DNA within the host’s genome.

“Although it had been previously identified by microscopy, we had not been able to separate the genomic signal from the host fish and the parasite until now,” said Javier del Campo, lead of the study and Principal Investigator at IBE and the Rosenstiel School.

“For the first time, we have been able to identify them through their DNA and place them within the well-known group of apicomplexan parasites.”

The team’s genomic data revealed that ichthyocolids belong to a previously uncharacterized group of organisms. This breakthrough will facilitate the detection of this parasite in future fish DNA or gut bacteria samples using the identified genetic barcode.

Implications for marine ecosystems and commercial fishing

The discovery has notable implications for commercial fishing and oceanic food webs, as the parasite is geographically and taxonomically widespread.

“Once we found ichthyocolids in the red-lipped blenny, a tropical fish, we wondered if it would also be part of the microbiota of other fish,” said Anthony Bonacolta, a PhD candidate in marine biology and ecology at the Rosenstiel School and first author of the study.

Subsequent analysis of a massive database of fish microbiomes revealed the parasite’s presence in most marine fish species studied across all oceans. This finding underscores the potential impact of such parasites on marine ecosystems.

Evolutionary insights and future studies

The research not only uncovers a new class of apicomplexans but also provides insights into the evolution of major parasites.

“The discovery of the ichthyocolids adds more context to this evolution. For the first time, they are placed as a sister group to well-known coral inhabitants, the corallicolids,” explained the researchers.

Studying ichthyocolids could illuminate basic traits of apicomplexans that may have clinical relevance.

“They may use similar infection mechanisms or have other similar biology which can enlighten our understanding of other apicomplexans,” concluded Bonacolta.

Future studies are expected to explore the prevalence and impact of ichthyocolids in marine ecosystems further, contributing to a better understanding of foodborne pathogens and their effects on global food webs.

Recent research into marine fish parasites has uncovered several significant findings that could enhance our understanding of marine ecosystems and improve food safety measures. These studies not only highlight the prevalence of previously unnoticed parasites but also provide insights into how environmental factors affect parasitic populations.

A study by the University of Washington revealed that climate change has significantly impacted marine parasites. The research, published in the Proceedings of the National Academy of Sciences, demonstrated that warming oceans have led to a decline in parasite populations, which could disrupt marine ecosystems contrary to initial assumptions.

The decline of parasites, which play a crucial role in marine food webs, might affect the balance between predator and prey species and potentially harm biodiversity​.

In a related study, researchers explored the complex interactions between fish parasites and environmental pollutants. This research, published in Parasitology, examined how parasites can influence the accumulation of pollutants in fish and how these interactions might impact fish health and parasite transmission.

The findings suggest that parasites can alter the effects of pollutants on fish, potentially reducing the toxic impact of these substances. This interplay between parasites and pollutants is critical for understanding marine ecosystems’ health and environmental monitoring’s reliability​.

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