Please write what is expressed in the foreign art song "Trout" as follows:

1. The first movement is a lively Allegro, sonata style. The piano plays an introduction that appears as a broken-down chord, and then the violin sings a beautifully serene, simple and tranquil main theme. After a slight expansion of the theme, the piano plays a lyrical sub-major part. After the more rigorous unfolding and recapitulation, the music ends with a short coda. This movement has a warm, bright and clear feeling, with beautiful and romantic ideas.

2. The second movement is in the Allegro, two-part form. The whole movement is quiet and gentle, the piano plays a wisp of the melody of the ballad winds that waft the atmosphere of the Alpine region in northern Austria. The lyrical, gypsy-inspired strains of the viola are interwoven with tenderness and sadness. The second section ends with a repetition. This movement is simple in form, but quite feminine and lovely.

3. The third movement is a harmonic piece. The rapid, brisk and spirited theme and the question and answer between strings and piano show a witty mood. The middle section is quiet and pleasant music in the style of Viennese dance music.

4. The fourth movement is in variation form. The popular melody depicts small trout swimming freely in a deep mountain stream. After a beautiful theme for violin, the piano plays the first variation. The second variation is led by the viola. The third variation is a mellow theme borrowed from the cello and cello, and the heavy music seems to evoke the sound of a fisherman's footsteps.

The fourth variation has powerful chords and bursts of sadness, as if the fisherman is casting his net and the little trout is struggling. The cello plays sympathy and sorrow in the fifth variation. A beautiful theme recurs in the coda, speaking of the eternity of freedom and joy and the beauty that will eventually come.