Probably caused by a virus
Cauliflower like tumor on the skin. Tumors range from pea size to several inches, depending on water temperature. Tumors are more prominent at cooler water temperatures (fall and winter) and sometimes regress in northern pike. Tumor may spread to inner organs.
Muskies and Northern Pike.
Believed to be a viral disease that may be transmitted by close physical contact, such as spawning. Transmission of the virus may be possible by physical contact during spawning and other close contacts.
Where ever muskies and northern pike are present. Quite common in Minnesota.
Due to a lack of concrete scientific knowledge about the disease, consumption is not advised.
There are no known methods of preventing this condition.
Dispose of uneaten portions by burying or in household waste. Fish entrails should never be discarded back into the lake.