Well, I realize I can sell them. I want to know if selling them is a bad idea from some reason.

I sell Magic Fish all the time - they really help the bank balance. The key is to know how to make them again when you want their benefits in your tanks.

Selling magic fish is both good and bad. It's good because like ladycfii said, they really help the bank balance, the bad thing is, if they aren't there, you don't get their benefits. Like ladycfii also said, the key is, just mass produce them, then sell the doubles.