Once when I worked at an aquarium in the Pacific North West a visitor stopped me to talk about how sad she was to see all these animals in tanks. (This is surprisingly common from visitors.) She mentioned the sunflower sea stars (Pycnopodia helianthoides) in particular. They were her favorite, and she used to see them all the time while diving locally and suddenly there were none, but we had them and that just didn't seem right.
We ended up having a lengthy conversation about how a disease, sea star wasting syndrome (SSWS), decimated the wild populations of that species and many sea stars a few years prior and how that aquarium was actually one of the few in the country exhibiting Pycnopodia that didn't lose their entire population to the disease. We talked about some of the research that was happening to help protect them and she started to feel a little better. She wanted to feel like it was okay for her to visit the aquarium and that she wasn't just staring at caged animals.
Pycnopodia are now listed as critically endangered. They are a keystone species in their environment and SSWS is estimated to have killed 90% of the wild population. Without them, the shores of the entire west coast have changed. Now, ten years later, that same aquarium was the first to establish a successful treatment for the disease. Before that, most aquariums had the protocol to remove symptomatic animal and generally had to euthanize them because nothing could be done. Within a matter of days, they were completely melted. Now, there is a treatment. It's not a cure, but there's hope that something can be done. That same aquarium is also part of efforts to work towards reintroducing Pycnopodia to the wild to help restore the ecosystems.
People have started to understand that zoos work in conservation and education, but aquariums do, too. We talk about the California condor and black footed ferret as success stories and Panamanian golden frogs and rhinos as works in progress, but aquariums are doing that same kind of work! There are coral conservation labs, efforts to reintroduce wild animals and remove invasives (looking at you, Florida), housing of non-releasable marine mammals, research into new medical procedures and treatments, and breeding of endangered species. The fish (and inverts!) in aquariums have an easy life, and might even be part of something so much bigger.
This is your permission to feel good about visiting reputable aquariums! Enjoy looking at the pretty, and not so pretty, fish (and inverts! please give the little sea bugs some love), and know that your admission is helping to keep them healthy and well cared for, and might even lead to something that can change the world.