Fish or fowl?

gistfile1.scala

trait Pet {
  type This <: Pet
  def name: String
  def renamed(newName: String): This
}
 
case class Fish(name: String, age: Int) extends Pet {
  type This = Fish
  def renamed(newName: String): This = copy(name = newName)
}
 
case class Chicken(name: String) extends Pet {
  type This = Fish
  def renamed(newName: String): This = Fish(newName, 3)
}
 
object FishOrFowl {
  def esquire[A <: Pet](a: A): a.This = a.renamed(a.name + ", Esq.")
  val f: Fish = esquire(new Chicken("bob")) // Oops!
}