Generally, one would be flattered if you asked for permission to photograph their aquarium, but some folks are very weary to the idea, especially fish stores. I can’t tell you how many times I’ve wandered into a store and the owner has had zero issue with me photographing their livestock. But there is that one store who does everything it can to protect its image, and denies you the picture taking experience no matter how beneficial it may be for them. If you want to take photos at your nearest store, ask for permission first. Do not just assume it is ok. Some stores post signs, while others may not. If you ever find yourself treading in a gray area, just walk away. There’s no sense getting into it with a local hobbyist or store owner because you want to indulge one of your other hobbies.