Liebstoeckl (Bupleurum rotundifolium) is a traditional herb used in old European cooking. If unavailable, you can substitute with a mix of fennel seeds and anise, or simply increase the oregano.
Liquamen is the ancient Roman fermented fish sauce. For a modern substitute, use fish sauce (like Nuoc Mam) or Worcestershire sauce, adjusted for saltiness.
This dish is best served fresh. The fish can become mushy if reheated excessively.