Henry -
Petland has a very small fish section therefore as they don't order very much they pay a higher cost than other stores. Then they mark it up to help cover their store operation costs and have some kind of small profit margin and there you go. Truthfully speaking, the fish section is really of little concern to the owner as they make their money from the dogs and cats they sell as they are the big money maker. They sell some of those dogs for $700 each! As long as people are crazy enough to pay that kind of money for a dog you can find in the classifieds for $150 to $250 why worry about the other little stuff?
Not bashing them or anything, it's just the the facts of life.