With increasing regularity in recent years, fishermen have caught largemouth bass with black blotches on their heads, bodies or fins.

Occasionally a fish is caught that is as spotted as a leopard.

The origin of these black blotches is a mystery to biologists.

Prior to the 1980s, no one seems to have seen them. The first one the author saw was in a photograph being circulated excitedly by a fellow biologist who worked at the Louisiana Department of Wildlife and Fisheries Fish Hatchery.

None of us had ever seen one before; now they are common.

The condition, called hyperpigmented melanosis for lack of a better term, naturally raises alarm among some fishermen — especially older ones — who remember when bass never had big black spots.

At first glance, the spots look almost cancerous, like melanoma. But they aren’t.

Some fishermen suspect pollution, diseases, parasites and even poor catch-and-release practices that result in stress on the fish.

But the truth is that no one has been able to document a link between the blotches and any causative agent. The black pigment is only skin deep and seems to have no effect on the fish or the edibility of the fish.