My guess is that these large fish are examples of some type of sea bass, though the many decades that have passed have eroded any memory of the fish type. In fact, even though I spotted my grandfather in about three milliseconds after looking at this picture, he seemed reluctant to give me much more than "yeah, that's probably me, but who knows?"
Not sure if he was just being self-effacing, or if he just didn't want to talk about Peleliu when we visited with him the other day.