Parasitic Worm Population Skyrocketing in Fish Species Used for Sushi

Sitting for lunch and spotting something unusual in your food is never pleasant. And, this may include sushi consumers spotting worms in their sushi. Yikes, right?

The chances of this happening today seem to be high. This is due to an increase in worms from Anisakis species that are infecting fish worldwide. 

Today, the number of fish with it is 283 times the number in the 70s, according to a report published in Global Change Biology.

The Dangers of the Anisakis Parasitic Worms

The worms from this genus, also known as whale worms, may lead to diarrhea and vomiting when ingested. The good news is that freezing the fillets destroys the parasites. And, farmed fish rarely gets infected with this parasite.

What’s more, fish suppliers and sushi chefs can spot and clean the worms that can grow up to two centimeters in length. Still, the rise in worm numbers isn’t good for certain marine species.

A group of researchers made an analysis of hundreds of scientific studies published since the 60s to find out the number of worms from two genera, i.e., Anisakis and Pseudoterranova per a single fish.

The data contained more than 55,000 specimens of 215 species of fish. In 1978, the first year for which the team had enough data for both groups of worms, they reported that less than one whale worm was found on average of 100 fish.

However, by 2015, they found more than one worm from Anisakis on average per single fish. This trend continued throughout the species and geographic regions regardless of the methods used for quantifying the worms.

They ranged from a simple dissection to dissolving the tissues of fish using acid. They didn’t note a global rise in the reports of pseudoterranova or the seal worm.

The problem with rise of Anisakis worms may be problematic for the diverse hosts of the wrigglers: the eggs of the worms may be taken up by krill and consumed by cephalopods such as squid. And, these are ingested by fish. 

All of them are consumed by dolphins and whales. The populations of any of these hosts may be at risk when there’s an abundance of Anisakis worms. 

The whale worms that infect the Atlantic salmon may lead to red vent syndrome as well as bleeding and swelling of the opening to the reproductive and digestive tract. 

During autopsies of whales, these worms are often discovered but it’s not clear how ill the animal could become, according to Chelsea Wood, a parasite ecologist from the University of Washington.

Abundant Enough for a Rising Parasite Population?

Because the Anisakis worms are increasingly common, they may become enough to support a rise in the parasite population.

If the host species populations were insufficient, the worms would have a hard time finishing the life cycle. So, the worms may be a sign that things are improving for the ecosystems of the oceans.

For example, the Anisakis worm increase may be a result of the rebound of certain populations of whales. These marine mammals play an essential role in the life cycle of worms. 

Anisakis can reproduce only in cetaceans. Another hypothesis that could explain the abundance of the parasites could be that the life cycle of parasites may be speeding up as the ocean waters become warmer because of climate change.

The team is also focused on discovering what the high level of parasites may mean for marine animals with a focus on the declining whale populations off the US West Coast. 

Despite these discoveries, Wood believes that preparers will do their best to remove the worms and appreciates sushi chefs’ abilities to spot and eliminate them from sushi.