Your question is not clear. If it is a song, the lyrics are a story. The author compares the fisherman to the ruler at that time and the trout to the people. The works profoundly and vividly express the dissatisfaction with the rulers and the yearning for freedom. It also reveals a profound social reality: kindness and simplicity are often tainted by fraud and evil.

If it is a trout in the piano quintet, it is more complicated, but it is also based on the story. This theme consists of five variations and an ending. Five variations can be based on the development of the story The mood is: 1. The children happily came to the river to see trout; Small trout swim freely in the river (piano playing theme variations1); The fisherman appeared, and the music suggested that the fate of the little trout was ominous; The fisherman stirred the river vigorously, and the little trout fled in panic, but was caught by the fisherman; The child has a heavy heart and is very sad. Conclusion: Return to the theme, express people's expectation and yearning for a better life, and despise the rulers.

I don't know. Does this work for you?