Which of these is classified as controversial fish in kosher dietary laws?

Swordfish is classified as controversial within kosher dietary laws primarily due to ambiguity regarding its scales. In order for a fish to be considered kosher, it must possess both fins and scales. While swordfish have fins, the nature and type of their scales have been debated among rabbinical authorities. Some groups argue that the scales of swordfish are not the kind that can be removed and possess the necessary characteristics defined by kosher law, thereby placing swordfish in a controversial position regarding its kosher status. The discussions surrounding these characteristics lead to differing opinions about its permissibility for consumption within Jewish dietary laws.

In contrast, the other fish listed—tilapia, mackerel, and perch—are generally accepted as kosher. They possess the requisite fins and scales as defined by dietary laws, making them non-controversial choices among adherents to kashrut.