ZURICH—Last month, Antoine Goetschel went to court here in defense of an unusual client: a 22-pound pike that had fought a fisherman for 10 minutes before surrendering.

Mr. Goetschel is the official animal lawyer for the Swiss canton of Zurich, a sort of public defender who represents the interests of pets, farm animals and wildlife. He wound up with the pike as a client when animal-welfare groups filed a complaint alleging animal cruelty in the fish's epic battle with an amateur angler.

The...