This shows the new Absorption property in version 11.5 and how to fine tune the property for a small fish model. Also look at the Wine Glass example that comes with Cinema 4D, located in Content Browser > Cinema 4D > Example Scenes > New Glass

If you are following the Step by Step tutorial, here are the steps in order:
Polygon Modeling
Joints
Cloner Object – Introduction
Cloner Object – Using Object Mode to animate
Target Effector
Optimizing Mograph Cloner for Display speed
Random Effector
Timeline
FCurve Offset to Delay Loop start
Specular and Diffuse Maps
Transparency Absorption
Refining Lights and Visible Volumetric settings