Among his numerous works, Paul Klee depicted various kinds of animals, in particular birds and fish. While animals have historically been a motif in a large number of Western paintings, depiction of them as a main motif is quite rare.In the age of the Renaissance, Hieronymus Bosch and Pieter Brueghel depicted fish which were symbolically relevant to Christianity and Christian culture. In the 20th century, Giorgio de Chirico also used fish as a religious symbol. Although Franz Mark introduced mammals in the main motif, Klee depicted birds and fish with unique and humorous forms and lines. Klee, knowing the aesthetic beauty, mysticism, and vital strength which are essentially inherent in fish and birds, wished to express these in purer and more primitive forms and lines.Fish in particular seldom become a central motif of painting. What Klee derived from fish is the simple forms and lines by which mammals may never be adequately expressed. Klee found essential beauty and freedom in the life of fish and in their swimming in aquatic nature. Furthermore, he found that drawing fish with simpler and more primitive forms and lines concurred with his ideas on art. The essence of fish, their vividness, agility, vigor, and energy as wildlife are expressed in their pure form. What Klee pursued through drawing fish is this pureness and beauty of life. On the other hand, Klee never failed to inspire a sense of humour and cynical insight into his symbolic expression of fish. Primitivism and symbolism are mingled sufficiently to realize his unique art. Paul Klee elaborately utilized symbolism and the style of primitivism, making fish a main motif in Western art in the 20th century.