I am currently looking into fishing the Wigan flashes after not fishing htem since i was a kid. Due to their size and the fact they are hardly fished they hold many secimen fish. As i have been talking to people, it appears they hold specimen Perch up to 4lb along with roach.rudd to 2lb+ along with large carp, tench and bream. HOWEVER, as they are rarely fished and they are very large, don't expect easy fishing but i imagine there are large perch. There are also some very large pike to boot!
Andy