The most practical way to learn how to rig 3D models in Blender is to start with a basic and simple exercise. The following is a tutorial written for novices that want to learn this beautiful art. Rigging a fish isn’t that difficult and this will give us the basic knowledge to utilize the technique.
We begin by loading our scene with a fish model created previously for this tutorial. Do this by going to File>>Append (Shift F1) and look for the file: “Fish.blend” where we can find the 3D creation. T o make it more interesting, I opted to model a Celacanto, a true living fossil. Once loaded, we save the scene.
It is now time to add a Bone for our fish which we do by going Add>> Armature>> Single Bone. The Bone has a body in the form of an Octahedron, a root (represented by a ball at the wider end of the body), and the tip (represented by a ball at the narrow end of the body). Both the tip and root can be selected separately.
The whole bone can be selected by clicking in the centre of the Bone.
Move the bone in such a way that the tip is amid the head of the fish, behind its eyes as shown in the picture.

Basic rigging of a fish-1.jpg

Give a name to the Bone so you can identify it from the rest of your Bones.
“Main” would be an appropriate name. In the panel on your right, look for the Bone panel represented by the small bone. There will be a field there to allow to you change the name of this bone from “Bone” to “Main.”

Basic rigging of a fish-2.jpg

Let us continue adding bones to our scene. This time we will make them by means of extrusion. Select the tip of the main Bone and with the E key, extrude the Bone that will move the head. Change the name of this Bone to “Head”.
We select the tip of the “Main” Bone again and extrude another bone away from the “Head” Bone with the E key.
We repeat the process until we have given the body of the fish several Bones that end at the tail (four in total). We assign the names: “Bone 1” through to “Bone 4” for these Bones.

Basic rigging of a fish-3.jpg

From the Main Bone extrude one Bone, then another to give us the Bone that will move the front upper fin. We will call this second Bone “Fin
1”. From Bone 2 extrude two sets of Bones that will connect with the Bones that will worque the rear upper and rear lower fins. Name these Bones “Fin 2” and “Fin 3” respectively.
Notice that we eliminate the Bones that connect Bone 2 with the Fin 2 and 3 (see figure).

Basic rigging of a fish-4.jpg

We assign the other bones to the remaining fins in a similar way and place them in the appropriate locations. Make sure you select the intermediate Bones between the fins and the Main Bone and eliminate them one by one. From the tip of Bone 1, extrude two more Bones for the body.
From the tip of Bone 3, extrude two more Bones for the fins of the tail. The result should look similar to the following image.

Basic rigging of a fish-5.jpg

It is now time to give a name to our skeleton.
We go to the Object panel represented by an orange cube. In the field that shows “ Armature” we substitute it for “Fish Bone.” A quite appropriate name.

Basic rigging of a fish-6.jpg

With all the bones in their place, we now have to prepare the mesh of the fish to unite it to the skeleton. It is necessary to abandon the Edit Mode through [T AB]. Select the mesh of the Celacanto, and look for the “Modifiers” panel (represented by a
wrench). In “ Add Modifiers” we assign the option Armature and in the field object we select “Fish Bone”.

Basic rigging of a fish-7.jpg

After this procedure, when you select the skeleton while in Pose mode, moving a bone will move the skin of the fish. Some imperfections can be corrected easily by toggling the “Envelope” option in the Armature panel.
We adjust the envelope in such a way that it covers the whole geometry of the fish by scaling the root of the bones with the S key in Edit Mode.
If done correctly, the envelopes will look like tin the figure.
Our clever fish can now recover life through the technique of animation and swim and travel in underwater environments generated by computer.

Basic rigging of a fish-8.jpg