These are my stats fishing in "Cantrips & Crows" for the Giant Sewer Rat. It seems like my stats are always on the high side, not sure if I am unlucky or not; but the stats are 100% accurate. I would however take them as the high end of the spectrum in terms of # of casts.
Sewer Carp: 55.7% (1172)
Magic Eater: 24.8% (521)
Empty Vial: 6.9% (146)
Drowned Rat: 5.5% (116)
Partially Eaten Fish: 4.0% (84)
Leaded Vial: 1.8% (38)
Crystal Vial: .6% (12)
Imbued Vial: .4% (8)
Enchanted Vial: .2% (5)
GIANT SEWER RAT: 0% (1)
Total Cast: 2103
On a personal note this was my last fishing achievement :P