Allison Little, a middle school assistant principal from Anchorage, has been fishing on the Kasilof River her entire adult life, so she’s used to seeing wormy parasites coiled up in fish on occasion.

The worms are about a centimeter (0.4 inches) long and tend to coil up in the fish muscle. They found that pulling the fillets apart with forceps allowed the team to count worm corpses accurately with ...