Here is what you can do if you really care that much about Walmart's fish that you need to yell at the manager.
1) Write a tactful (no swear words or death threads) letter to the following folks:
a) Store manager
b) District manager
c) Regional manager
d) Company CEO, President, and Board of Directors
Explain exactly what made you unhappy, tell them you will rally others to boycott their store if something is not done, and also give them possible solutions.
2) Stand around the fish department and discourage other customers from purchasing their fish. Hand out educational literature about ich. Have people sign a petition you can mail with your letter above.
Unfortunately fish are not protected by any Animal Welfare Act, nor do pet-shops or Walmarts fall under USDA juristiction. The only thing your local ASPCA would be able to do is give them a warning. But technically speaking, Walmart is not breaking any laws. Neither are Petcos, Petsmarts, or any other LFS that carries fish or birds. Hamsters, gerbils, guinea pigs, ferrets, dogs, cats, and non-human primates are the only animals protected by Federal Animal Welfare. Each state might have other legislation to cover rats and mice, but no where do they cover fish, birds, or reptiles.
The only way to get big corporations to listen is to hit them where it hurts, the profits. Only by not shopping at these places =at all= will that be effective. Even if you boycott Walmart fish, when you buy toilet paper there, you're still only promoting their fish department.
Good luck.
~~Colesea