It takes a year and a half to grow a red bellied pacu to that size, less for a black. There really isn't any proof that the fish is any older than that. I would say, given the circumstaces, evidence points to this fish is lucky to be older than two years old. Has anyone actually SEEN a healthy full grown black pacu in person? They look NOTHING like that. If that was a healthy full grown black pacu, there is no way in hell a 75 would stand up to it's strength for any length of time let alone 40 years.