Buiodda's Crafting mod calls for dried perch skin for a number of recipes, but I fail to catch the elusive buggers.
I thought you'd catch them (together with roaches, which I don't really care about) in small lakes, but my attempts at setting nets in a single tile lake has resulted in, I think, everything except perches, roaches, and salmon (and the last one shouldn't be available there).
Neither the in game info nor the wiki sheds any light on the issue.