This past May I had the opportunity of being sent to Pearl Harbor on business and stayed at the Marriott on the end of Waikiki that is near the aquarium. Even better, Bruce Carlson, ex-director of the aquarium, spoke at our reef club meeting this past summer and I had the opportunity to speak with him for a while at a barbeque held at one of the member's houses.
Regarding the gigas clams, Bruce was there in I believe 1982 when he said that he received the two gigas clams. One was already 5 years old (the one that now was weighed in at I think over 170 pounds), and the other gigas was aquacultured and a baby. Bruce said that from what he can discern the one is the oldest in captivity and the other is the oldest living aquacultured clam. Interestingly he also says they have the oldest living coral in captivity which is believe it or not a goniopora that they got in the seventies.
Here is a pic of me in front of the tank with these two gigas...