Black spot is caused by a parasite called a fluke which burrows into the skin of fish. The fluke itself is actually a white color. Yellow grub is caused by flukes which burrow into a fish and curl up into a sac under the skin, in the muscle or in internal organs. These flukes are often found near the dorsal fins, but occasionally in the organs. When freed from the sac, flukes may be up to one half inch long.
White grubs are a fluke that penetrates the skin and forms a sac in the kidneys or liver.
These grubs are similar to but smaller than yellow grubs. Its origin and how it is spread are not known. The virus appears to infect other species of fish, including smallmouth bass, bluegill and crappies, but has only been associated with death in largemouth bass. Previously, the virus had been found as far north as Missouri, Tennessee, and Kentucky. Do not move any fish, live bait or fish parts from one water body to another.