We have an allied proverb sometimes referred to as "the New Golden Rule":
He who has the gold rules.
Doyle, Mieder & Shapiro, The [Yale] Dictionary of Modern Proverbs (2012), expresses this saying somewhat differently:
He who has the gold makes the rules.
Whoever has the gold rules.
The earliest citation of its first formulation is from 1967 (referring to an earlier Wizard of Id cartoon).
A much older and very well known expression of the same idea is "Might makes right," which I suppose includes the right under big-fish law to eat little fish.
Or again, to invoke the spirit of Anatole France, "The law, in its majestic equality, permits big fish and little fish alike to gulp each other down."
And to top things off, we do have the saying "Big fish eat little fish" in English. Here is the entry for that proverb in Martin Manser, The Facts on File Dictionary of Proverbs (2002):
big fish eat little fish Small organizations or insignificant people tend to be swallowed up or destroyed by those that are greater and more powerful ... The proverb was first recorded in a text dating from before 1200. In Shakespeare's play Pericles (2:1), the following exchange occurs between two fishermen: "'Master, I marvel how the fishes live in the sea.' 'Why, as men do a-land—the great ones eat up the little ones.'"