Hello there. To make a traditional Russian ukha that acts as a real belly filler in the old grandmother style, you want to start with a good base. First, boil small river fish wrapped in cheesecloth with whole onions and carrots for the rich broth, then discard them.
Next, add chunks of potatoes and a handful of pearl barley or rice to make it hearty. Finally, add the main noble fish chunks like pike, perch, or whitefish, along with peppercorns and bay leaves, simmering gently until tender. Finish with fresh dill and let it rest before serving.