He was a kind man and simply let her go free. After hearing the story, the fisherman's greedy wife sent him back to the sea—she needed a new trough.
The fish granted the wish, and a new trough magically appeared at the old couple's hut.
But the fisherman's wife now wanted more: a new house, to become a noble lady, and, eventually, the the Queen of the Land.
Every time she sent her old husband to the shore, the golden fish would fulfill the wishes. However, the woman now wished to be the Empress of all Land and the Sea, and the golden fish to be her servant.
The fisherman went back to the shore, called the fish and explained the last wish of his wife. The golden fish disappeared without a word.
When the old man returned home, he found his old mud hut, his poor old wife, and the original broken trough.