I was shocked as a kid seeing tuna in an aquarium up close and realizing how big they were. The aquarium kept them in the same tank as the sharks and honestly, I was more intimidated by them than the sharks.
I had to look it up - only a couple of aquariums in the world have bluefin (the largest species) in captivity, most that keep tuna have yellowfin and skipjack, large fish but not nearly as big as bluefin.
Similar experience albeit with a documentary. I was shocked at how big and imposing they were.
I think I never saw life tuna, but I still remember the scenes from 'The Outsiders of Uskoken Castle' as a kid (the book/TV series is also known as 'Red Zora')
There are species of tuna that can reach up to 4.5m. But most canned tuna is Skipjack or Albacore and they can "only" get up to 0.8m (skipjack) and 1m (albacore).
Still pretty big though. But the huge ones are mostly sold at auction for sushi afaik