Im actually convinced the exotic ones are bugged, as someone that goes for every triumph in the game these are the only ones i don't have. I spent 10 hours one week fishing trying to get 1 of the exotic nessus ones since I only need 1 left for that triumph. I probably got between 10-20 exotic fish but every single one was the default exotic fish that was available the first week, and that I don't need the triumph for. These are probably going to stay uncompleted just like the BS expedition triumph during season of the plunder. Whoever makes these triumphs obviously is padding players for more playtime.