Scientists Detect First-ever Known Infectious Cancer in Fish

Scientists have detected the first known infectious cancer in fish. Genetic findings suggest melanoma cells may be transferred from one fish to another. According to the research published in the journal Nature, melanoma tumors seen in brown catfish living in lakes in the Canadian province of Quebec and the northeastern United States are more genetically similar to tumors in other fish than to the fish they are found on.

This indicates that cancer cells may be transferred from one fish to another. One of the leaders of the research, Prof. Julie Dragon stated that infectious cancers are extremely rare in nature. Reminding that infectious cancer has only been detected in Tasmanian devils, dogs and shellfish to date, Dragon said that the new finding is the first example recorded in fish.

However, the first cases were noticed by fishermen in 2012 in Lake Memphremagog, located on the border of Quebec and Vermont. It was later understood that the black spots and masses seen on the catfish were melanoma type skin cancer. In the intervening years, the disease has become widespread in the lake, and today it is stated that approximately one-third of the brown catfish in the lake have these tumors.

It is not yet known exactly to what extent cancer affects fish. While the disease spreads to organs such as the brain and liver in some, it is noteworthy that many fish appear healthy despite the lesions and can live to old ages. Carcinogenic substances carried into the lake were initially suspected because the black lesions appeared the year after major flooding caused by Tropical Storm Irene.

However, the analyzes did not reach a definitive conclusion. Another study published in May reported higher levels of seven metals, including zinc and carcinogenic arsenic, in the skin of fish with tumors. View Full Size Interestingly, in 2014, it was investigated whether the disease was caused by a virus, but no virus was found in the genetic examinations.

The researchers then considered the possibility that the fish might be prone to cancer due to inbreeding. As a result of genetic comparisons of samples taken from healthy fish, sick fish and tumors, it was seen that the population had high genetic diversity, meaning that there was no inbreeding. The most striking result of the study was related to the genetic structure of tumor cells.

Under normal conditions, cancer cells are largely similar to the cells of the living thing from which they arise. However, this study revealed that the tumor cells are more similar to each other than the fish they are found on.