The following are SPOILERS! for the game. If you don't care about the math going on behind the scenes, read no further and just go with the motion of the oceans!
Here are the complete statistics for how often you catch fish, and what rarity you catch for Level 0 through Level 5. Any level past 5 has the same chances as Level 5. Levels beyond 5 do not improve your chances -- they just earn you cooler and cooler titles.
The statistics work like this. You have XX% chance of catching a fish. IF you catch a fish, then you have XX% chance of catching one of each of the different rarities. The rarity percentages are not "per casting" but "per catch"!
Note that "streaks" of misses AND streaks of hits are entirely possible. There is no streakbreaker code in the game to force you to hit or force you to miss. Random numbers are completely random, so over long periods of time your statistics will match these, even if in small windows of time they don't seem to match.
As for the levels, you require the following amounts of XP to reach each level. We'll keep the titles themselves secret, to keep from completely ruining the fun...
TO REACH LEVEL ???, YOU NEED THIS MUCH XP:
7Seas Fishing Game // Copyright 2008, 2009, 2010