Agreed with most of the above, though calling out specific ISOs is a bit premature. Once you reach the limits of aperture and shutter speed, use whatever aperture you need to get the right exposure.
If you're good at handholding, you might be able to use a slower shutter speed for some of the "still" subjects like seahorses.
The 70-200 is likely to be too long for this instance, though at the wide end it might work for some things, especially given the extra stop of aperture compared to the 24-105.
My best advice would be to look for the light. If you're going with family or friends, watch how the light comes out of the aquarium glass to light the face and silhouette the body. Don't be afraid to let the meter think you're underexposing - as long as the important parts of the image are properly exposed, then your histogram might not be a perfectly centered hill.
Work with the color of the lighting to preserve the "feel" of the aquarium's ambiance.
This isn't my shot, it's a buddy's shot from the Georgia aquarium:
http://blog.tobiasroybal.com/2011/07/aquarium.html
If you look for his facebook page, he's got some from this year's Dragon Con event at the Georgia Aquarium. I can't link to it from here, sorry, but it's easy to find if you google "tobias roybal aquarium."