edit: isn't there a plugin for this? if not... put the second color to whatever color you want and the primary one to full transparent and then click on the grandient tool and chose raidal grandient
then try to do that with the picture
it took me about around 30 mins to make this... and it wasnt really easy.... but think it turned out to be a weird fish that lives in the ocean... and imagin the eyes and stuff... because thats what the imagination is used for