In Chinese Mythology, the Peng and Kun are different forms of the same creature. Translated from the ancient literature, Zuhang Zi's 'Xiao Yao You' :

There lived a kind of giant mysterious fish in the northern sea. These fish are called Kun. Nobody knows how big these fish actually are. They can turn into giant birds. When they are in bird form, they are known as Peng. Nobody knows how big these birds actually are. When they fly, their wings are like the colorful clouds in the sky. When there is a storm in the northern sea, the Peng will fly to the southern sea. They travel three thousand (Chinese miles) in one flap of their wings. They can fly for six months without rest.

Note: the southern sea mentioned in the story is also known as Tian Chi.

Wikipedia, 2004. Peng (mythology). [Online] (Updated 4 November 2009) - http://en.wikipedia.org/w/index.php?title=Peng_(mythology)&action=history