When the bones of one fin are created and adjusted, to save some time you can copy them to the other side using mirror tool. Select all bones in the fin. Click on Mirror tool and adjust position in Mirror tool window.
Now select first bones in side fins on both sides. Use select and link tool and link those two bones to the first bone we created (blue arrows). At first I linked those bones to the second bone (red arrows) but when animating I got better results with those blue arrows linking, and you will see latter why. Now every bone we created is a part of the skeleton.
When you hide the body this is how the skeleton looks like.
So I forgot to add a back fin bone. Do it now in right or left viewport. And then select the bone and link it to the second bone in body.
You probably notice that all the time I been calling bones: first bone, second bone...
Its a little bit difficult to understand and to follow me. So imagine a more complex bone skeleton and deferent people working with same model and trying to talk about some parts of it.
So we are going to add a name for an every bone. Now at this stage, for as are important only three bones so you follow the picture at left and the rest of bones name like you want.
Skeleton is created, now its time to connect skeleton with skin (mesh). Select the shark body (mesh) and add a Skin modifier. Click an Add Bone button and select all bones. Now the bones are part of the model. Try to select one and move it or rotate it.. see how the body moves with it. But something is wrong. Not all the parts of the mesh are moving with the bone. That's because every bone has an envelope around itself. Envelope define space around the bone and every vertex of the mesh that finds in that space will move with the bone.
Lets try to adjust our bones to the mesh. Select Body bone. If you find difficult to click on bone use selection filter on main toolbar. In drop down menu select Bones. Now you can select bones only.. While Body bone is selected click Edit Envelopes. Envelope is shown. You can scale or move the Envelope. See that red vertexes?, movement of the bone will effect them the most. Main front part of the shark should be in the envelope of the Body bone.. Now do this for every bone.
At the end to check connection select the Main bone and move it. The model and all its parts should move with the bone. Any part that stay in place is not connected well. That mean that you need to adjust the bone envelope near that part of the mesh.
Its time to start with animation. Firstly place a Target camera, facing shark. Make sure that camera is not too far away, so you can clearly see the shark. Select the Camera Target and link it to the Main bone. The main shark movement will be done by moving Main bone so the camera will always look at the center of movement. At these three images around you can see the main path of the shark body...
Select the Main bone. Turn on Animate button. Move the time bar to the frame 80. Move the Main bone just down next to camera. Now move the ruler to frame 100, and move the Main bone away from the camera like the picture below shows.
Now turn off Animation button. Turn on play. In top view you will see how the shark moves and camera follows. You will notice that while shark goes away from the camera it keep straight forward position like its not turned to the left. That means that we have to rotate sharks body around frame 80.
Go to the frame 85, turn on Animation button, select Main bone and rotate it so the shark's head is almost facing turn left direction (final destination of the movement). Now go to the frame 90 and rotate the Main bone so the head is facing turn direction. Turn off Animation button and play anim. Something is wrong. It looks like shark is starting to rotate from the start. That's because we add a rotation in frame 80 and Max automatically starts rotation from the frame 0. Every change in Animation is written in keys. And you have a key for rotation, position, scale of the every animated element on every frame.