White Spots in Smelts Appear to Be a Type of Tapeworm or Nematode

Observation by Samantha Hill:

Smelts caught in Chevak had white spots in the flesh. The tomcods caught at the same time were fine. Shared with Erica Lujan via Facebook

Jayde Ferguson, Fish Pathologist with the Alaska Department of Fish and Game, writes:

These appear to be encysted helminths. They look similar to larval tapeworms, such as Diphylobothrium, but probably represent a different species. They could also be encysted nematodes, such as Anisakis, which are also helminths and quite common in marine fish. It’s difficult to tell which helminth from the photo.

Comments from LEO Editors:

In his response, Jayde provides links with more information from the "Diseases of Wild and Cultured Fishes in Alaska." We have summarized some of the information from those links below.

Helminths are worm-like parasites that include flukes (trematodes), tapeworms (cestodes), and roundworms (nematodes).

There are three species of tapeworm found in Alaskan fish: Diphyllobothrium, Schistocephalus, and Triaenophorus. Diphyllobothrium are found in more species of fish than the other two types of tapeworm, and is the only one known to infect people. The Centers for Disease Control and Prevention (CDC) recommend cooking fish at about 153 degrees Fahrenheit for 5 minutes, or freezing the fish at -4 degrees Fahrenheit for 7 days to kill the tapeworm larvae before you eat the fish.

The nematode Anisakis can be found in marine and anadromous fish around the world. They're often recognized in their larval form as tightly coiled worms in the flesh of the fish. Anisakis are also known to infect people, and the CDC recommends the same cooking and freezing guidelines as they do with Diphyllobothrium: cook fish at about 153 degrees Fahrenheit for 5 minutes, or freeze the fish at -4 degrees Fahrenheit for 7 days to kill the Anikakis larvae before you eat the fish.