According to the article, it just seems that Idaho was trying to maintain some kind of yellow perch fishery, and was thus being very selective on what other fish were stocked.

In general, I think Yellow Perch and Walleye usually exist together.

Correct me if I'm wrong, but I thought they were in the same family.

Excerpt from Robert Crais' "The Monkey's Raincoat:"
"She took another microscopic bite of her sandwich, then pushed it away. Maybe she absorbed nutrients from her surroundings."