How do you catch an Eel on Mysims Kingdom?

First, you need a fishing pole. I think you can get one from the fisher guy. He is by the beach. Then, you have to get close to the area where you want to fish. Once you get there, a blue fish icon will pop up in the top left corner. Tap on that and you start to fish!

Now for catching. When you start to fish you can move the bobber around the water. You will notice that music starts to play. That can sometimes help you. If a fish goes directly over to your bobber and lands on it, you can rapidly tap the bobber with you stylus(stick) and catch the fish! If you don't want that fish, you can wait for another one to come.

I hope I helped!