When I make calls like this, I always start out by saying "I wasn't personally in your store, but I have a friend who was and was telling me about the conditions of your store so I felt compelled to call and chat with you about...." (or re-word it if you were the one that saw it yourself) and then I go on to tell them what I've read here (or tell them what you've seen in the store).
When you call there, always ask for a manager. If you ask to talk to someone in the fish dept. they're certainly not going to pass along the message because it will reflect poorly upon them.
Before you hang up, also say "And would you mind also giving me the district manager's phone number also?" and then they should share it with you. Give the dist. manager a call also.
I haven't ever had a manager be upset with me, in fact they are always more than willing to be very accomodating to whatever I have to say. Sometimes I have to leave the store and cool my head off on the drive home because I'm too irate, but in cases where I need to show them something right away, the courage comes from somewhere.
And finish it off by going to www.walmart.com/storefeedback and fill out the form.
They don't know you're disgusted unless you tell them. OVER AND OVER.
If the conditions don't get better, but in fact get worse, do something more drastic. Call the SPCA if you have one in your area, report them. Call the Humane Society. OR - if it's outright animal cruelty, call the Animal Control in the area. Sometimes that means calling the Sheriff's Department. Those kind of calls are my favorite. You KNOW when it gets to that point that someone's butt is probably gonna be fired.
Good luck, and if you want another body to call and complain right along side you, I'm ALWAYS ready to, and I always have anytime cell minutes to spare!!
This way, you can hide behind your phone. 
