there's a book about this subject...
on a personal note:
my almost 4 year old loves music. she has several CD that i've burned for her. one of them has fun/satire tunes...Allan Sherman, The Chipmonks, and a bunch of Dr. Demento stuff. one tune, "Fish Heads" is one of her favs. during the chorus: fish heads fishes heads, rollie pollie fish heads, fish heads fish heads, eat them up, yum.
she always says fish cats...and insists that the phrase is fish cats.