I learned by studying my fish finder while at anchor what the perch look like as they swim by under the boat. If I was in 34 fow, I would see a black line appear on the fish finder at a depth of 31 ft and start getting hits and fish. No line, no action. Sometimes it would be a thicker line like a ribbon or several smaller lines like fingers, I would call that attack formation because the action would be fast with many doubles. My fish finder will pick up my crappie rig, so I would lift the bait to match the exact depth of the line of fish and that seemed to work well. So that is what I call a line of perch.