Citrus bergamia, as it's known in botanical circles, first showed up 300 years ago in Southern Italy, the result of crossbreeding a sour orange with "something else, " variously identified as a citron, a lemon, a limeor a Palestine sweet lime.
The acid from the lime, lemonor orange juice changes the structure of the proteins in the fish much in the same way that heat does. (If you make it at home, you can observe the flesh turning from translucent to opaque.) Therein lay my answer.