I'm about to piss a lot of people off, but the best way to stop it is to quit rescuing the petstore fish. You buy one, and 4 more take it's place. I used to help order fish at a petstore I worked at years ago, and if 1 went out, 4 more were ordered on the next shipment. If the fish keeps selling, they will keep them in stock. As soon as the sales go down, the fish is no longer carried.