The Esox lucius were avoiding the poisoned areas. The method was impractical, but did reduce the number of Coregonus clupeaformis effected by worms by thirty-nine percent. The head is short and slightly pointed. Pelvic axillary process present, spawning males have developed strong tubecles on their sides. The back is grayish blue, sides silvery, and the belly is whitish.
Young fish have several parr marks on each side.
Mature whitefish migrate during the late spring and early summer upstream to cooler waters. Adults remain upstream through summer until spawning in October and November. P. williamsoni are around 3-4in. They spawn in the fall when water temperatures are around 40-45 o F. Eggs hatch in March, around 5,000, which are placed over gravel and small rubble where the current removes any silt from acquiring. The eggs are adhesive and stick to stream substrate.