So, you think you've got something great? Well, maybe, but this is how it works. When you click on it to open (get the treasure) there is a 20% chance to get an Uncut Crystal. If that fails then there is a 15% chance to get a Silver Bar. But if that fails, there is then a 15% chance to get an Uncut Sapphire. This fail check continues until there is a success which is why there is a 100% for the Raw Pearl Clam which requires every other item to not be selected. It is your consolation prize.
Item Nominal Rate% Actual Rate%
Uncut Superior Grade Crystal Uncut Crystal 20% 20.0%
Silver Bar Silver Bar 15% 12.0%
Uncut Superior Grade Sapphire Uncut superior grade sapphire 15% 10.2%
Uncut Superior Grade Emerald Uncut superior grade emerald 15% 8.67%
Uncut Superior Grade Ruby Uncut superior grade ruby 15% 7.37%
Uncut Superior Grade Diamond Uncut superior grade diamond 10% 4.18%
Gold Bar Gold Bar 10% 3.76%
White Gold Bar White Gold Bar 10% 3.38%
Uncut Superior Grade Amethyst Uncut superior grade amethyst 10% 3.04%
Platinum Bar Platinum Bar 10% 2.74%
Azurite Bar Azurite Bar 10% 2.47%
Fire Stone Bar Fire Stone Bar 5% 1.11%
Uncut Superior Grade Black Opal Uncut superior grade black opal 10% 2.11%
Uncut Superior Grade Jadeite Uncut superior grade jadeite 10% 1.90%
Wings of Path Wings of Path 50% 8.54%
Poseidon's Permission Poseidon's Permission 2.5% 0.21%
Pluto's Permission Pluto's Permission 2.5% 0.21%
Sylvanus's Permission Silvanus's Permission 2.5% 0.20%
Raw Pearl Clam Raw Pearl Clam 100% 7.91%

Can be Obtained From Edit

Fishing Level Item
20 Cage
25 Fishing Rod
50 Wooden Harpoon
50 Fishing Net
70 Steel Harpoon

Chance to catch varies with your Fishing Skill. Right Click each fishing spot and Check Drops to see yours.