This Porcupinefish (Diodon hystrix) is one of the largest I have seen.  He was well over 3' long.  I found him on the inner drop-off at Mixing Bowl in about 35' of water and stalked him for many minutes before I was close enough for a decent shot.  Even though they are quite common here, it's difficult to get closer than about 10' to them because they are extremely shy.