Probably a channel cat, their in alot of ct waters, including the ct river, quinebaug, pachaug river, shetucket, and french river. Ive caught many during day and night while fishing for carp with oatmeal. As for your question on biggest northeast freshwater fish, if we exclude any anadromous species its between channel cats carp and northern pike in my opinion. Pick up an anglers guide it gives a list of waterways alphabetically and lists MOST of the fish in them.