This drawing was created relatively early in Picasso's career: it was completed in 1903 and he was born in 1881. It is, perhaps due to its subject matter - a woman having sexual intercourse with a fish - one of his less famous and least talked about drawings.

Nevertheless, it is an important part of his oeuvre. Its bold lines and recognisable yet strong and larger than life figures mark The Mackerel out as an Expressionist work of art.

This is unsurprising because Picasso is one of the world's most famous Expressionist artists (though it is worth noting that Expressionism did not begin in Picasso's native Spain but rather in Germany at the beginning of the 20th century).

One of the other artworks by Picasso that it is most tempting to compare The Mackerel to is his 1934 drawing of a woman whose genitals take the form of a giant fish, which is often also called 'The Mackerel'. In both the 1903 sketch and the 1934 drawing, Picasso places great focus on the fish's tongue.

Art critics have speculated that the 1934 version of The Mackerel, which is more detailed, is a richly symbolic, allegorical piece. In this drawing, the eponymous mackerel is depicted drinking blood, which some commentators have speculated is a reference to Christ and Mary Magdalene and the Christian practice of taking communion.

The Mackerel is by no means the only quirky, unconventional sketch by Pablo Picasso. Throughout his career (which ended with his death in 1973 in France), Picasso sketched numerous different human and animal forms. Other sketches include a drawing of a dog using just a few lines and a depiction of a woman entitled Nude Seated on Left Leg.

The Mackerel is perhaps most interesting because it depicts the meeting point of human and animal forms at an early stage in Picasso's career. Perhaps for Picasso this is precisely where the erotic lay: in the breaking of taboos and the blurring of boundaries. The Mackerel is a work that will appeal to lovers of erotic art and anyone who is interested in discovering more about the life and times of Pablo Picasso.