site.btaHydrobiologist Eliza Uzunova to Study Pathogens that May Endanger Fish Health in Antarctica

In an interview for BTA, hydrobiologist and ichthyologist Prof Eliza Uzunova said that she is part of the 32nd Bulgarian Antarctic Expedition to work on a project about fish health. “Our goal is to study all kinds of pathogenic agents (bacteria, viruses, parasites) that may endanger fish’ health status. We will also do research on the presence of microplastics in the water that may have reached the shores of Antarctica and that fish mistakenly use for food,” she explained. 

In Antarctica, Prof Uzunova will try to continue the work started by her colleague, Assoc Prof Petya Orozova, and catch fish to be studied within the scientific project. 

To shed light on the importance of knowing how fish in Antarctica react to various factors, Prof Uzunova welcomed the BTA team at the Faculty of Biology of the St Kliment Ohridski University of Sofia, where she teaches hydrobiology in Bachelor’s programmes and ecology of fish and aquacultures in Master’s programmes. 

Fishing and restoration

The science of studying fish is extremely important, because it has a socio-economic significance. “The hydrobionts – the organisms that we can take from ecosystems to feed humanity apart from fish, some crustaceans, and mussels – are not many. Therefore, we should not just take them from the world ocean, rivers, and lakes: we have the responsibility to restore them in some way,” the expert said. That can partially be done through their artificial breeding in the so-called aquacultures, which is what Prof Uzunova teaches students.  

In her words, she has dedicated over 25 years to the science about fish. She researches and studies various parts of Bulgaria to assess the state of fish species as well as their habitats. Her knowledge and interest have taken her to the project on the breeding and restoration of the freshwater species European bullhead (Cottus gobio).  

Fish of Antartica: risks and research  

One of the important characteristics of Antarctica’s biota [the animals and plants living in a particular habitat] is that 90% of the species there are endemic, meaning they cannot be found anywhere else on Earth. Antarctica’s fish species are endemic and thus have very unusual biological characteristics. For example, their blood lacks haemoglobin, i.e. they lack a structure transferring oxygen in their organisms, and their skeletal system is poorly mineralized. They produce substances that prevent their tissues and the liquids inside from freezing, Prof Uzunova explained. 

However, these unusual characteristics make fish in Antarctica vulnerable to various stress factors. Among the risks is climate change, which increases the temperature in the atmosphere and water, makes glaciers melt and thus increases freshwater. Other risks are water pollution, overfishing for industrial purposes, and foreign species displacing local ones.  

The dangers fish in Antarctica face have made Bulgarian scientists launch a project on fish health. In the last years, there has been news of fish with severe skin tumours. Scientists have found that these are caused by X-cell parasites of the Notoxcellia genus, Prof Uzunova said. The scientific community believes that this is a consequence of climate change. “That is why we have set ourselves the task of forecasting how climate change will affect fish microbiome – the millions of microorganisms that live on skin, in the digestive system and all internal organs. It is important to know what this microbiome’s structure is, because its balance influences the overall health status of fish but also of humans, since we consume fish,” the expert explained. Many microorganisms do not generally cause diseases to their host, but changes in the environmental conditions can make them pathogenic and even result in an epidemic, she specified.

Another problem the Bulgarian scientists are focusing on is antimicrobial resistance, which is the ability of microorganisms to become ever more resistant to antimicrobial remedies to which they were very sensitive until recently, Prof Uzunova told BTA. Her project also aims to find probiotic bacterial strands producing antimicrobial substances, which can be used to counteract antimicrobial resistance. 

To that end, the most important thing for an ichthyologist is to obtain fish for research. The Bulgarian naval research ship Sv. Sv. Kiril i Metodii, which is part of the 32nd Bulgarian Antarctic Expedition, does not yet have a special device for catching fish, which the other big research vessels are equipped with, Prof Uzunova noted. “We catch our fish for research with meshy devices we place in the water. My colleague Petya Orozova was the first Bulgarian researcher to make an improvised lab aboard the ship,” she explained. 

Microbiological samples were taken from every fish on the ship to test them in the corresponding food environments, she specified. When the samples collected by Assoc Prof Orozova were brought back to Bulgaria, the research continued in several laboratories: at Sofia University’s Faculty of Biology, at the National Diagnostic Research Veterinary Institute, and at the National Centre for Infectious and Parasitic Diseases. 

It would be nice to have enough fish – between 100 and 150 individuals - to guarantee that what is observed is not accidental but something typical for the fish fauna in the area of Antarctica, Prof Uzunova commented. Due to the limited number of fish from the 31st Antarctic Expedition – 40 fish from the species Notothenia coriiceps and Notothenia rossii, the result obtained is not complete and worth reporting. Prof Uzunova hopes to catch more fish with the necessary equipment she has prepared, including at a greater depth in order to diversify the species of fish the Bulgarian scientists will study.

Microplastics: a danger to marine life as well as people

Microplastics have a long life; they often “live” for over 400 years in water ecosystems, becoming a part of the food chain. Some of them fall apart to nanoparticles, which can end up in fish’s liver and damage it, Prof Uzunova explained. The plastics themselves become carriers of bacteria that have genes for antimicrobial resistance, and some plastics contain substances such as Bisphenol A (BPA) and plastificators that can cause hormonal and reproductive damage. Fish health being affected by the ingestion of microplastics harbours a risk to humans as end consumers, the expert underscored. 

What is the most frightening is that the quantity of these plastics is huge. At present, between 5 and 12 million tonnes of plastic waste is dumped a year, and their quantity in the world ocean is estimated at over 150 million tonnes. If the forecasts are correct and that quantity continues to be stably dumped in the ocean, by 2050 there will be as much plastics as fish in the ocean, Prof Uzunova commented. 

“That is why we are interested in what quantities of plastics reach Antarctica, and the hypothesis is that they are small, thanks to that continent being far away. However, there are recent research showing that the plastic is already there,” she warned.  

Together with her colleagues Assoc Prof Petya Orozova, Dr Borislava Margaritova, Dr Zornitsa Zaharieva, Dr Ekaterina Mileva, and Dr Dimitriy Dashinov, Prof Uzunova will continue doing research on Antarctica in search of data on the human impact on fish as well as possible solutions to the situation. 

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During the 32nd Bulgarian expedition to Antarctica, which started on November 8, 2023, the Bulgarian News Agency (BTA) is publishing interviews with Antarctic researchers. The Bulgaria-Antarctica BTA's Log again provides coverage of the voyage of the Sv. Sv. Kiril i Metodii to Antarctica and back and its stay there, as it did during the 31st expedition between December 27, 2022 and May 2, 2023. Back then, only BTA had a correspondent, Daily News Editor Konstantin Karagyozov, who covered the 127-day expedition with text, video and photos during the entire voyage (including across the Atlantic in both directions) and throughout the stay in Antarctica. In June 2023, BTA published in Bulgarian and in English an issue of its LIK magazine "To Antarctica and Back under the Bulgarian Flag" dedicated to the historic expedition.

Again, all of BTA's information on the Bulgarian scientific research in Antarctica and the support provided by the Bulgarian naval research vessel, as well as on the other activities at the Bulgarian Antarctic Base, will be available to all media outlets in Bulgarian and in English on BTA's website in the Bulgaria - Antarctica: BTA's Log section.

BTA has a National Press Club on board the ship and is planning to open a National Press Club at the Bulgarian Antarctic Base on Livingston Island.