In a compelling intersection of nature and science, researchers from the University of Cambridge and the University of Vermont are investigating a perplexing phenomenon: contagious cancer in brown bullhead catfish. Scott Young, a seasoned fisherman from New Brunswick, has observed these fish bearing unusual dark spots for over 40 years. This May, he collaborated with post-doctoral researcher Zoe Clarke to collect specimens, hoping to confirm her hypothesis that these lesions may signify a transmissible form of cancer linked to findings from a distant lake.
The Discovery of Transmissible Cancer
Clarke’s ongoing research delves into the alarming implications of a transmissible cancer first identified in catfish inhabiting Lake Memphremagog, a body of water straddling the Canada-U.S. border. Between 2014 and 2018, studies revealed that the raised black growths observed on these fish were, in fact, skin cancer. More recently, a team from the University of Vermont published findings indicating that this melanoma is not merely a byproduct of environmental factors but a contagious disease capable of spreading between fish.
In a paper featured in *Nature*, the researchers characterised this contagious cancer as “a puzzling biological phenomenon,” emphasising its potential to severely impact local fish populations. This catfish melanoma is only the fourth distinct lineage of naturally-occurring transmissible cancer discovered in the animal kingdom, joining the ranks of malignancies found in dogs, Tasmanian devils, and various shellfish.
Genetic Insights and the Search for Origins
Dr. Julie Dragon, a microbiology and molecular genetics expert at the University of Vermont, led the study that unveiled the genetic similarities among the tumours, indicating they are clones rather than separate mutations. Typically, cancers closely resemble the host’s DNA with minimal genetic deviations. However, analyses of the affected catfish have shown that the tumours are genetically distinct from their hosts, arising from a single parasitic cell lineage that has propagated through the fish population over time.
This discovery raises crucial questions about the cancer’s origins. Dragon speculated that it likely did not originate in Lake Memphremagog, as evidence suggests its presence in lakes across New Hampshire and Maine. Clarke’s outreach efforts to identify further cases yielded a promising lead last October when a doctoral student reported similar lesions in New Brunswick catfish. Now, as Clarke awaits DNA results from samples taken in New Brunswick, the research team is keen to unravel the timeline and location of this cancer’s emergence.
The Next Steps in Research
With plans to return to New Brunswick next year, Clarke aims to expand her investigation along the Saint John River, targeting less populated areas. The researchers are actively seeking assistance from the public; they encourage anyone who encounters catfish exhibiting lesions to document their findings and report them for further analysis. “This collaboration could be vital in piecing together the puzzle of how and why this phenomenon is occurring,” Clarke remarked.
The implications of studying this fish cancer extend beyond the immediate ecosystem. As Dragon noted, investigating the pathology of melanoma in these catfish may shed light on the disease’s development and progression, potentially offering insights that could benefit human health. Unlike humans, who often develop skin cancer due to UV exposure, these catfish thrive in muddy environments and forage primarily at night, prompting questions about the underlying mechanisms at play.
Concerns for Human Health
For those concerned about the risks of consuming these infected fish, Dragon reassured the public that there is no evidence suggesting that this transmissible cancer poses a threat to human health. Nonetheless, the U.S. Fish and Wildlife Service advises against eating fish that display visible lesions or growths, maintaining a precautionary approach.
Why it Matters
This research highlights not only the intricate connections between species within ecosystems but also the broader implications of disease transmission across the animal kingdom. As scientists endeavour to decipher the origins and mechanisms of this contagious cancer, their work may offer crucial insights into the nature of malignancies and their potential impacts on biodiversity. Understanding such phenomena could inform conservation efforts and public health advisories, ultimately fostering a greater appreciation for the delicate balance of life in our waters.
