According to research published in the journal iScience, these tumors are caused by a parasitic infection, the effects of which are being worsened by climate change.
The authors discovered the grotesque-looking fish on an expedition to West Antarctica in 2018. They noticed that in two species of crowned notothen, around 30 percent of specimens had the tumors. They were pale pink, raised, rough, and often covered more than a third of the surface of fish’s bodies. The researchers had visited that same area, which includes Andcord Bay and Dallmann Bay, four years prior, but found no examples of fish with these tumors.
“As soon as we got the first trawl back on deck, we realized that one species was really abundant, and a lot of them had big tumors,” Thomas Desvignes, lead author of the study, said in a statement. “When we saw that, we immediately realized we had to do something.”
Once the team returned to the lab, they analyzed the tumors and found that the fish had X-cell disease, a cancerous infection caused by a new species of Xcellidae, a parasitic alveolate (the same type of protozoa that causes malaria). Wild fisheries in Iceland and Norway have previously reported infections by Xcellidae, but how it’s transmitted is not yet known.
Nototheniod fish are infamous for their adaptations, which allow them to live in the coldest waters on the planet. The fish evolved a glycoprotein that lowers their blood freezing point to just below the freezing point of seawater (28.4 F), enabling them to survive in the frigid Antarctic waters.
The researchers posit that the sudden and dramatic uptick in infections by Xcellidae may be related to increasing seawater temperatures as a result of climate change.
“Although sea bottom temperatures at our capture sites were not dramatically different than those at other nearby localities, glaciers on the West Antarctic Peninsula are melting at a rapid pace, affecting Antarctic bottom waters, which have warmed and freshened for several decades,” the authors said in the paper.
The warmer waters may improve the dispersion or infectivity of Notoxcellia, the new Xcellidae species found to be infecting the Antarctic fish, or potentially weaken the icefish, making them more susceptible to infection.
“When life conditions become challenging, animals become more prone to disease,” said Desvignes.
Increased global temperatures caused by climate change are also heating the ocean. To the west of the Antarctic Peninsula, upper ocean temperatures have increased over 34 F since 1955, with the Antarctic Circumpolar Current warming at a faster rate than the rest of the Southern Ocean. This combined with the resultant melting of sea ice is already causing knock-on effects across the Antarctic ecosystem, seeing long-term decline in the abundance of Antarctic krill, and changes in penguin distribution.
“While we currently lack the data and knowledge to predict how X-cells might be affected by global climate change, with alarming forecasts for continued changes in Antarctic climates, this dramatic situation in this population may forecast large-scale biotic changes in host-parasite interactions triggered by changes in the abiotic environment,” said the authors in the study.
The authors added that they need to perform more research to better understand and to quantify the parasitic infection, how it’s spread between fish, and how climate change will affect it long term.
“We’re preparing project proposals to go there again and study this specific outbreak, how it evolved since 2018, and explore adjacent areas to try to see whether we can detect the pathogen elsewhere and in other species,” Desvignes said in a statement.
