This strange condition can affect both smallmouth and largemouth bass. Little is known about the cause of these markings even though this condition was first observed in the 1980s. It is believed that this hyperpigmented melanosis may be a result of catch and release or is a natural defense mechanism against environmental contaminants. There isnt a lot of conclusive evidence to support either theory 100 percent, but considering both pollutants and catch and release have increased over the years, you expect that these blotches would be extremely common by now.
The marks seem to eventually disappear, suggesting they may be part of a skin or slime repairing process. Ive also noted that they seem to disappear faster from smaller adult bass. The largest fish seem to hold them for at least two years.
