Scientists have discovered that black skin growths on catfish in lakes across New England and Canada are caused by a contagious form of cancer. This is the first time such a transmissible cancer has been found in a freshwater fish species. The study was conducted by a team from Vermont. They found that the cancer cells do not behave like typical tumors. Instead, they spread from one fish to another in a way that is more similar to how parasites move between hosts. The black skin lesions were observed in catfish from Lake Memphremagog and other lakes in the region. According to the researchers, this discovery challenges the common understanding of how cancer spreads. Typically, cancers develop within an individual and are not passed to others. However, in this case, the cancer cells themselves are transmitted between fish. The findings could lead to new insights into how cancers evolve and spread in different species. Further studies are planned to understand the mechanism of transmission and how it affects the fish population. The team hopes their work will help in understanding similar processes in other animals, including humans.