Of course, fish don't have lungs!!! (I should have known this)
It is not a slice of lung that Jason gave me but a slice of pyloric caeca. (I wouldn't have known this)
Jason has just confessed that he had forgotten the word for this organ when he gave it to me and had simply said, lung. Apparently, the pyloric caeca assists primarily in absorbing nutrients, but it also absorbs oxygen into the blood stream.
I am glad to know of this scientific fact.
However, I like the poetry of fish lung.