Not sure if I'll do it, I fly every week for work, and I'm pretty savy going through security
what you ahve to do it call ahead of time, and ask to talk to the TSA supervisor, and tell them your coming through with a live fish,etc --they may ask if you have permits, or a fish store receipt, etc
they will not x-ray the bag of water/ cooler of water, etc but will hand inspect it, and will need to see something alive in the water--such as a fish swimming around (not sure how this would work with corals)
there is a provision in the liquid carry-on policy that allows this
but call first so they can expect it coming through--they might even tell you what security checkpoint to go through
I've never done it, but just researched it