the fish always stinks from the head downwards

The freshness of a dead fish can be judged from the condition of its head. Thus, when the responsible part (as the leaders of a country, etc.) is rotten, the rest will soon follow. Gr. ἰχθὺς ἐκ τῆς κεφαλῆς ὄζειν ἄρχεται, a fish begins to stink from the head.

1581 G. PETTIE tr. S. Guazzo’s Civil Conversation III. 51 If the prouerbe be true,..that a fishe beginneth first to smell at the head,..the faultes of our seruantes will be layed vppon vs.

1611 R. COTGRAVE Dict. French & English s.v. Teste, Fish euer begins to taint at the head; the first thing that’s deprau’d in man’s his wit.

1915 W. S. CHURCHILL Letter 3 Dec. in M. Gilbert Winston S. Churchill (1972) III. Compan. II. 1309 The guilt of criminality attaches to those responsible. ‘Well,’ said the Aga Khan, ‘fish goes rotten by the head.’

1981 Sunday Telegraph 3 May 16 ‘The fish’, as the saying goes, ‘always stinks from the head downwards.’ Last Sunday we deplored Mr. Michael Foot’s liking for the street politics of marches and ‘demos’. Since then, a hundred Labour MPs..have followed their leader’s example.

2002 Washington Post 19 Mar. A21 Cardinal Law has to go. The Vatican has to speak up. This fish, as they say, rots from the head.