Articulated Dolphin. Print in Place. 0.1mm layer height !!!! No supports required. Suggest gradual infill.
If you want to really make sure the joints work and don't break, better print at 150% or more, still 0.1 layers. (One of the makes uploaded is 0.2mm layer height. That will not work. And I don't want to make the tail thicker and I can't include more tolerance.)
Just use hot needle and push through fin if you want to hang it somewhere....
Version 1.5 corrects a Problem with one of the joints highlighted in a comment.