Was out 10/12 on Sodus Bay, no jumbo perch. Had to pick through a ton of dinks to get enough eight-inchers for a perch fry. Largest perch was 9". Things should heat up after the cold and wind this weekend.
I fished Henderson week of Sep 14. Six hours of drifting all over Bay and we caught one 4 inch perch. Could not even catch a goby! Screen on fish finder was blank for most of the day. No other boats fishing as far as the eye could see. It was a liquid desert out there. Worst day we ever had at Henderson.
The question of whether or not sea lamprey are native to Lake Ontario is far from being settled.
See: R. L. Eschenroder, "Comment: Mitochondrial DNA Analysis Indicates Sea Lampreys are Indigenous to Lake Ontario". In, Transactions of the American Fisheries Society, Vol 138(5):1178-1189.
http://www.tandfonline.com/doi/full/10.1577/T08-035.1#preview
Sure looks like a Cisco to me. Also known as Lake Herring (Coregonus artedi). If you still have the fish, you could take it over to the USGS Biological Station at Wrights Landing in Oswego for a positive ID.