Three religions and nine schools of thought (also known as nine schools of thought and three schools of thought) generally refer to ancient religions and various academic schools in China, and are the ranks of the status and professional names of ancient people in China. It also refers to various industries and people in society. In ancient vernacular novels, there are often derogatory meanings.
Metaphor is that bad people mix with good people.
Dragons and fish are mixed together.
[Pinyin]
[Source] Zhang Tang He Zhi's "The Fisherman's Word" XIII: "The wind stirs the sky waves, and the dragons mix in one river."