I don't know for sure. My book (The Encyclopedia of Exotic Tropical Fishes) said that on page 726. I've seen pics of ones that look a mile long and took 5 men to hold up.
8-9 feet is actually the common wild size these days. Before back then they grew to 12-14 feet. Overfishing of the bigger ones caused them to disappear and with the smaller one left in the wild and breed. The offspring also a carries the gene of the parents that are 8-9 feet or smaller, thus the size of them being an adult is also small.
Captive size is around 5-6 feet. Sometimes bigger.