I totally agree with Slug.
You could take the matter further and offer to help the guy out. Either donate your time or see if he'll hire you as an occasional employee. A couple of hours a week could make a huge difference in the tanks (organizing fish, identifying ill fish to get them into hospital tanks, pulling dead fish from tanks, showing the other employees how to care for the fish).
Of course, this suggestion is coming from a guy who's got quite a bit of free time on his hands. I understand that not everyone can afford to do something like this.
At the very least, though, go back and visit the store periodically to see if you can see a difference in the way things are happening.
You might also be able to help find a place to move the arrowana and catfish to. It's not an easy task, and if the manager is focusing on getting the tanks okay, he may not have time to look around. Some e-mails to local aquariums may turn up helpful info.
Of course, offering to help in any way will help you determine if the manager is actually meaning to make changes, too.
