From Chris Royston, regular collaborator here at Into Spanish Translation Blog:

Codfish (bacalao) has an important historical role in Iberian history. Not surprisingly, this is reflected in idioms. "Te conozco bacalao aunque vienes (vengas) disfrazado" literally translates to "I know you codfish even though you come disguised". The equivalent phrase in English is "I can see straight through you" or "You can't fool me". Another idiom is "Cortar (partir) el bacalao" which literally means "To cut up (divvy up) the codfish". The colloquial meaning is "To be the boss".

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