Unless you're a diver, as I am not, you may find that aquarium animals can be a bit harder to relate to than traditional zoo animals. Tucked away behind glass, you can't hear them or smell them. In a way, the displays are just like those fish screen-savers you see - movement and color, but removed, distant, and alien.
A major goal of zoos and aquariums is to inspire the public to develop an appreciation for wildlife. It can be hard to get people to feel a connection or be inspired to care about something so separate from us. We're an interactive species, and we like to use all of our senses (well, not all of them at all times...). The result, cropping up at aquariums and nature centers around the world, is the touch tank.
The concept of the touch tank is pretty simple. It's a tank where you... touch things. Living things, specifically. Virtually every aquarium large and small has a touch tank these days, where visitors can get their hands in the water to feel fish, mollusks, and other aquatic organisms, under the careful supervision of aquarium staff. I haven't been able to find out much on the history or origins of the tanks, but I know they've been going back for decades. Growing up, the National Aquarium in Baltimore was the aquarium I visited most frequently, and I remember their touch tank well. It was removed a decade or so ago to make way for new exhibits, but came back in a big way this year with the aquarium's new Living Seashore exhibit. Here, horseshoe crabs, whelks, starfish, and moon jellies can be gently handled by visitors.
By far, the most popular touch tanks around the country are sharks and rays. People love sharks... and by "love," I mean "tend to be terrified of," so giving visitors a chance to touch a shark (of a small, harmless species) is an incredible experience that many participants won't soon forget. Years ago, temporary sting ray feeding stations (all named, invariably Sting Ray Bay) were traveling around the zoo world. They were so popular that many zoos decided to host them as permanent fixtures. The rays are made "safe" for visitors by having the stinging barbs at the end of their tails trimmed off, a painless procedure (so I'm told) that in no way harms the ray.
Speaking of safety, though...
Obviously aquarium officials are going to make sure that touch tanks are safe for visitors - hence no piranha or moray eel touch tanks that I know off. The question is, how safe are they for animals? Doubtlessly there are some fish and invertebrates which are relatively well-suited for these types of enclosures. They have to be comfortable in shallow water and tolerant of disturbance and handling; fish that will get stressed too easily need not apply. The fact that people are reaching in and out of the water also raises the possibility of contaminants entering the water - lotions, perfumes, soaps, etc. Perhaps these are the sorts of things that the filtration systems can easily handle.
Supervision is essential. I'm willing to believe that a horseshoe crab will tolerate plenty of stroking on its carapace. I have a hard time believing that it will put up with banging - all visitors need to be monitored closely and instructed on what is appropriate or not. Lastly, having time limits and break-periods for the animals is also a must. When a friend and I visited Adventure Aquarium recently, it seemed like we reached each touch station right as it was going on break. Sure, we were a little frustrated that we barely got chances to touch the sharks and rays, but we understood - the animals needed rest and privacy.
I think there needs to be more research done into exhibit tank vs touch tank fish - water quality, stress levels, lifespans - just to give some hard, empirical data to examine. From what I've seen, however, a well-planned touch tank - one that is manned responsibly and stocked with appropriate species - can be a tremendous boon to any aquarium. Certainly it gets people relating to fish and other aquatic creatures and making personal connections, and that should be a key goal of any aquarium.