From the fascinating movie "Catfish" :::
"They used to tank cod from Alaska all the way to China. They'd keep them in vats in the ship. By the time the codfish reached China, the flesh was mush and tasteless. So this guy came up with the idea that if you put these cods in these big vats, put some catfish in with them and the catfish will keep the cod agile. And there are those people who are catfish in life. And they keep you on your toes. They keep you guessing, they keep you thinking, they keep you fresh. And I thank god for the catfish because we would be droll, boring and dull if we didn't have somebody nipping at our fin."