What does it mean to draw lots for carp lying on the ice?

The story in Twenty-four Filial Pieties. In ancient times, there was a dutiful son whose name was forgotten. His mother was ill and wanted to eat crucian carp soup, but it was cold at that time, where could I eat fish? The dutiful son ran to the ice and lay there trying to melt the ice through his own body temperature and catch a fish to honor his mother.