Hey guys i want to rig a fish , do somebody has an idea of how to do it?
The spine is a good application for spline IK, since you can have as many bones as you want for smooth deformations and still keep the number of controls to a minimum. You can run the bones down the middle of the fish - you don’t need to use the actual biological backbone - since most fish don’t bend much in the ventral-dorsal axis You can treat the tail as an extension of the spine or as a separate FK control.
Lateralf fins are usually simple FK; depending on the fish they may be rigid (in which case, one bone each) or more flexible, in which case you’d approach them more or less like a bird wing.
Dorsal or ventral fins can be quite rigid with minimal fk for pose tweaking (eg, a shark), or they can be ribbon like (eg Dory from Finding Nemo). For rigid fins, its usually simple FK.
In the case of ribbones, you can use a spline running along the outer edge of the ribbon with the individual bones ik’d to targets which are constrained to the spline. That way you can coordinate movements of the ribbon on a simple control instead of making the animators hand manage lots of them. You can control it with clusters or with a sine wave deformer, which is nice for sending ripples along the spline in a smooth way with few keys. The deformer and thee clusters are not mutually exclusive, you if the sine deformer is the first deformer in the history you can animated the clusters over it. If you have a spline IK spine you might also want to use its control spine as a wire deformer to deform the ribbon control spline - that will subordinated the ripples of the ribbon fin to the movement of the whole fish.
Pay close attention to where you place the jaw hinges, on fishes they tend to be much lower than on land animals.
Many fish can flap their gills; this is a nice way to add some life and expression to the faces which don’t naturally have a lot of expressiveness.