Why do I need to know gros poisson? 

Because while we assume that readers of The Local are not involved in organised crime, you never know. 

What does it mean?

Gros poisson, pronounced “groh pwah-sonn” means big fish.

But when used as an expression, it means an important or influential person. 

It is slang which comes from the world of policing and is often used to talk about crime bosses, kingpins and gang leaders. 

In this context you can use gros poisson like this: 

On a arrêté plusieurs gros poissons – We have arrested several crime bosses

Vito Corleone est le gros poisson du milieu italien – Vito Corleone is the head of the Italian mafia 

It can also be used in a more general sense, not necessarily in relation to crime, to refer to anyone who is a big figure, important or influential.

Emmanuel Macron est le gros poisson de l’état français – Emmanuel Macron is the big dog of the French state”

Si tu fais beaucoup d’effort, tu pourrais devenir le gros poisson – If you put in lots of work, you can become the big boss

In French, gros poisson dans un petite mare (big fish in a small sea) is the equivalent idiom to “big fish in a small pond” – ie someone who is important but only within their own small group. 

It is used by the rapper, Orelsan, in one of his songs. 

The chorus contains the lyrics: 

Un gros poisson dans une petite mare // Le roi des fourmis, le prince des sous-fifres// Un gros poisson dans une petite mare// J’te parle de bluff, d’excès d’orgueil, d’abus de pouvoir// Un gros poisson dans une petite mare// Le roi des fourmis, le prince des sous-fifres// Un gros poisson dans une petite mare// On trouve toujours plus fort que soi, c’est ça la morale de l’histoire

A big fish in a small pond// The king of the ants, the prince of the underlings// A big fish in a small pond// I am talking to you about bluffing, an excess of pride and an abuse of power// A big fish in a small pond// The king of the ants, the prince of the underlings// A big fish in a small pond// There is always someone stronger than you, that is the moral of the story

Synonyms 

In French people do not say le grand fromage to mean the “big cheese” or big boss. 

A better way to convey that someone is a big player, whether involved in crime or not, is grand manitou. 

Elle est un grand manitou de l’industrie – She is a big figure in the industry