Green bug attached to my fish

Question
I bought four fish a few days ago and put them in my tank, yesterday i noticed a green thing moving on one of their backs. I pulled the fish out and took the bug off and put it in a glass to observe and since then it looks to have laid a hundred or so eggs. It is a very funny looking bug. It is not more then a half inch round. It is a see through green, with a white tummy, it looks like a flat flounder almost except it has two black eyes and 8 feet/fins underneath and two little fins on the back and it swims SUPER fast. I assume it is bad for my fish but i though i would keep it and see if i can find out what it is before i get rid of it. Any ideas?

Answer
Hi Ryan;

It sounds like argulus, also called "Fish Lice". They are a parasite so you don't want to keep them or put them back into the tank with your fish. Here is info about them and how to treat your tank to be sure they are all gone;

http://www.ponddoc.com/koihospital/Diagnostic/Parasitic/Argulus.htm

At Your Service;
Chris Robbins