And the Lord said to Noah, "Noah, it would pleaseth me if you doth build me an Ark". Being his obedient servant, Noah readily agreed.
God then added, "just one thing Noah, I only want it populated with one particular species of fish". Not wishing to incur the wrath of the Almighty, Noah said nothing and steadied himself to the task in hand.
"One more thing before you start" God interjected, "it must have many tiers to it". Noah was beginning to be a bit confused and said, "let me see if I've got the details right oh Lord of mine, what you are asking me to build is a multi-storey Carp Ark".