With higher rank lures you can get a higher chance at catching the fish. That is one thing and also there are multiple ranks of fish. If you use a fish lure of lower rank than the fish is, it has a higher chance to escape.
There are currently only rank 1 and rank 2 fish catching spells and rank 1 and rank 2 fish.
I called them rank two and five because those were the levels you get the lures. At fishing level 2 I was able to buy all lures besides Ice of course so I called them rank 2. When I got to fishing level 5 I was able to buy the next set of lures so I called them rank 5.
yeah, i think the fishing is still in a beta sort. its still fun to play! although i must admit, first, i didnt know where to find the higher ranked lures, then i assumed the fishing feature was still in beta.