In columbo episode s10 e14 around 1:54 Columbo indicates that he heard the 1 gallon per 1 inch of fish rule and had it checked out and it is actually true ! Now everyone knows Columbo wouldn't lie.
He was ! He was fishing for a corpse !He always played dumb to draw the bad guys out. I think that's the one inch per gallon comment's basis. He was fishing for something there...