I think some wonderful advice has been shared here... hats off to you guys!!
When you ask someone else to select a fish species for you, please remember that we don't have any clue to what you are seeking in a pet. That is like telling us you want a puppy, and asking us to suggest the breed for you... yet we know nothing about you or your lifestyle. You could be a St Bernard person and others would be suggesting a toy poodle. Can you give us something to go on besides a 200 gallon tank?
Are you seeking something predatory? You say large, but how large do you mean? Even in 200 gallons there will be some limits to the animals you can keep. How many other fish do you wish to keep with your "main selection"? Is this to be a reef tank, fowl, or somewhere in between? Do you desire inverts? What type of lighting will you be working with? What kind of filtration are you planning to use? All these things make a difference.
My first suggestion to you would be to study the various options of environment and decide which appeals to you most or go to some of the online marine places and start browsing marine fish species at random until you see something that appeals to you. Once you find a list of species that appeal to you, it is then easier for us to get a feel for what you like, and suggest other options in the same category of animals, or other options with the same traits/habits/etc of the things on your list. You may find 3 fish you like but only 1 of them can have tank mates in a 200 gallon tank... what is it you liked about the bamboo shark that inspired you to want one so badly? Is it because it is a shark? There are a few options of shark that could live in a 200 gallon tank, but you won't get much if anything else in there with it, if anything at all.
Try looking up these species and see if any of them appeals to you...
Marbled catshark (Atelomycterus macleayi)
Coral catshark (Atelomycterus marmoratus)
Bali catshark (Atelomycterus baliensis) (We kept one of the bali catsharks at our store in the display for many yrs. This is a great species for anyone who wants a "shark" in captivity. They have the elongated body, beautiful markings, and tend to have a more docile nature vs some of the other catshark species. This is a reef shark species, and very flexible... which is why it can handle a 200 gallon tank where others cannot. Ours was strictly a hand feeder, although some of our staff had to use a feeding stick to avoid being bitten. If you take the time and work with the shark every day, hand feeding with one of these is usually pretty easy and somewhat safe. I never used a feeding stick and never had a problem.)
I must warn you now, before you go any further... Each of these species of shark that I named can be quite difficult to find, and they each have very specialized needs. This is not something that will be inexpensive or easy to keep, but it sounds as if you are willing to commit yourself to whatever care requirements you come up with.
Before you purchase any marine animal for your tank, there are a few things you will need to know up front.
1. Be sure the animal is eating before you take it home, and this is most especially true of any shark species. Don't just take someone's word for it, insist on seeing it eat or walk away. It is very common for stores to bring in marine animals who never eat while there, and when they get to the home aquarium they starve to death. Stress is a huge factor in feeding marine animals, as is the food selections. Many marine animals are still being wild caught (the majority of them), unlike freshwater where the majority is now being captive bred for the hobby. Getting a wild animal to take prepared foods can be quite difficult and sometimes impossible.
2. Be sure the fish doesn't have any abrasions or injuries before you spend your money. Open wounds/lesions is a warning sign that this animal has health issues that can be difficult, expensive, and sometimes impossible for the average home aquarist to deal with.
3. Once you know the animal is eating, find out what foods it is taking and have that on hand when you get the animal at home. Introducing new foods can take time and marine animals can be a lot fussier about what they will eat. You'll want to be sure to have on hand something you know for sure they eat while you transition them to new/better foods.
4. Beyond the first animal (invert or otherwise) be sure you have a quarantine tank set up that can accommodate the sizes of the fish you will be bringing home. Medicating marine fish can be quite difficult, and dangerous to tank mates, and disease/illness issues are not always apparent at the time of purchase. Disease and illness spreads quickly in an aquarium.
5. Know and understand the environment these animals come from before you attempt to replicate it at home. This is something commonly missed, especially by newbies. Knowing that these animals are primarily coming from a wild environment, the best chance at success is to replicate their natural habitat as closely as possible. This includes foods, rock structure/formations, corals, tank mates, water chemistry, temp, light cycles, etc. A marine animal will need proper rock structures, caves, etc in their tank vs a bunch of plastic plants and sponge bob ornaments, which is another big difference between freshwater and marine keeping. Knowing and understanding their environment is a major factor, especially when you work with a shark species. (Adding the wrong substrate, such as crushed coral, for a bottom dwelling shark can quickly lead to the death of the animal when it rips its belly open on sharp crushed coral pieces, etc)
I hope this helps you sort through your options. Best of luck to you.
And to the rest of you.... keep up the good work!!!