But an aquarium on a cruising boat is great for the kids. Set it up right, with air and filters as you would at home. See what you can find, learn about it, and let it go. You will not need as good a set-up as you would for marinefish at home - one of the mini 2 1/2 gallon tanks will do fine, placed in the kid's cabin.
"Climbing (sailing) is like fun, only different."