Fishing
Fishing is a Warrior/Babarian based skill found in World 2 through the left portal in town.
The Fishing area contains a Fishing Rack 2 Fishing spots a whale named Whattso that gives a couple of Fishing related quests and a portal to the next Fishing area. (requires level 15 Fishing)
You can start fishing as soon as your character has access to the second World, Yum Yum Desert. Simply click on the fish you can see swimming in the water and your character will begin fishing. Eventually he will pull a fish from the water which will fly up and bash you in the head causing damage to your character, however, if your character has enough defense, no damage will be taken. Each type of fish requires a certain amount of defense to endure.
For example: my fisherman has 26 defense and takes 25 points of damage when hit with a Hermit Can.
Now onto Efficiency. Efficiency works a little different here than in other skills. Besides the amount of fish you get, Efficiency also effects which type of fish you get too.
Straight off the bat you have 100% efficiency for the first fish, Goldfish
50 Efficiency is required to have a chance to catch Hermit can
200 Efficiency is required to have a chance to catch Jellyfish
400 Efficiency is required to have a chance to catch Bloach
See how i said 'chance' to catch? That's because when you have enough efficiency for the next fish, your percentage for the fish before gets reduced and added to the next.
Another example: My fisherman is level 11 fishing, has 193 efficiency, using fly as bait, spoons LoI line and Copper Fish Rod, my percentages are 68% for Goldfish and 32% for Hermit can.