Demystifying Worms in Tuna: What Do They Look Like and Are They Safe?

Tuna is prized around the world for its delicious taste, versatility, and nutritional value However, tuna also tends to harbor parasitic worms that can pose health risks if consumed. For tuna lovers, especially those who enjoy sushi and sashimi, understanding what these worms look like and how to identify them is key

In this article, we’ll explore the appearance, types, and risks of worms commonly found in fresh tuna. Read on to get the facts and decipher myth from reality when it comes to tuna worms.

Worms in Tuna Vary in Size, Shape and Color

When inspecting fresh tuna meat, either raw or cooked, you may come across worm-like strands of varying sizes These parasites can resemble long thin threads or specks embedded in the flesh.

In terms of color, tuna worms can range from difficult to see transparent worms to more visible red, white pink or brown worms. Texture-wise some worms in tuna have a jelly-like appearance while others look more fibrous or stringy.

Worm sizes also run the gamut from tiny microscopic worms impossible to identify with the naked eye to worms up to 2 centimeters long that are readily visible, especially in thinly sliced sashimi.

• Long, thin threads or strands
• Small specks or jelly-like blobs
• Red, white, pink or brown coloring
• Transparent to clearly visible
• Microscopic to up to 2 cm long

If you spot any of these worm-like shapes in your raw or undercooked tuna, it’s generally safest to assume they are indeed worms and to cook the fish fully or discard it.

The 3 Most Common Worms Found in Tuna

Tuna are susceptible to infestation from a variety of marine worms and parasites. However, a few specific worm types make up the bulk of tuna worm concerns:

1. Anisakis

One of the most prevalent worms found in tuna is Anisakis, a nematode or roundworm. Anisakis worms burrow into the flesh of fish like tuna and salmon. They appear as thin, white, thread-like strands that can grow up to 2 cm long.

Anisakis can lead to a disease called anisakiasis in humans if ingested via raw or undercooked fish. Symptoms include nausea, vomiting, and abdominal pain.

2. Pseudoterranova

Another nematode worm called Pseudoterranova is also common in tuna. These worms look similar to Anisakis, appearing as long, thin, white strands in tuna meat.

In humans, Pseudoterranova can cause pseudoterranovosis, an infection marked by diarrhea, vomiting, fever and stomach pain.

3. Echinorhynchus

A type of acanthocephalan worm called Echinorhynchus gondo can also be found in tuna. These worms have a distinct spiny proboscis that anchors them into the intestinal wall.

Visible worms appear red or brown and elongated. An Echinorhynchus species called E. lageniformis causes echinorhynchiasis when humans ingest infected tuna or other fish.

Why Take Precautions with Tuna Worms

Seeing worms or worm-like shapes in your fresh tuna can understandably trigger the alarm bells. But are all these worms truly a cause for concern?

The answer is a qualified yes. Many tuna worms pose minimal risk to human health. However some, like Anisakis and Pseudoterranova, can lead to gastrointestinal issues or abdominal pain if consumed.

Immune-compromised individuals and children face higher risks from inadvertently eating worms in undercooked tuna. Women who are pregnant should also take extra precautions.

That said, not all worms in tuna automatically lead to sickness. Worm types, numbers and overall tuna quality all factor into the level of risk posed by the presence of worms.

When in doubt though, it’s better to be safe than sorry. Thoroughly cooking tuna to an internal temperature of at least 145°F kills any potential worms. Also inspect sashimi-grade tuna closely before consuming raw.

How to Identify Worms in Your Tuna

If you want to eat tuna with confidence, whether cooked or raw, it helps to know how to identify worms:

• Examine the tuna closely under good lighting or against a light background. This makes worms easier to see.

• Check for long, thin strands or jelly-like bits that resemble worms in shape. Compare to photos online.

• Slice sashimi thinly to expose any hidden worms not visible in thicker cuts.

• Look for movement. Live worms may wiggle or move slightly.

• Smell for fishiness or ammonia odors that suggest spoilage and higher worm risk.

• Inspect the belly flap, vent, and flesh close to bones, common worm hotspots.

Again, when unsure if something is a worm, err on the safe side. Thorough cooking or freezing can kill worms.

Pro Tips to Prevent Worms in Your Tuna

Since worms occur naturally in tuna, some exposure is unavoidable. However, you can take steps to reduce the likelihood of worms:

• Purchase sashimi or sushi grade tuna from reputable sellers. This denotes its safe for raw consumption.

• Avoid turbid, mushy, or foul-smelling tuna as this reflects poor quality.

• Check tuna flesh closely for worms before cooking or serving raw.

• Freeze tuna to below -4°F for over 7 days to kill parasites.

• Cook tuna to an internal temperature of at least 145°F to kill any worms present.

• Clean all surfaces and utensils that contact raw tuna to avoid cross-contamination.

• Consume tuna in moderation, especially higher-risk individuals.

Proper handling, thorough cooking, and common sense precautions go a long way in preventing illness from tuna worms.

Tuna Worms Under the Microscope

Some worms in tuna are too small to see with the naked eye. To identify these microscopic worms, you need to examine tuna under a microscope.

Common tuna worms visible under magnification include nematodes, cestodes, trematodes, acanthocephalans, and copepods. Their appearance varies widely – while some have distinct heads and bellies, others appear more ambiguous in structure.

Microscopic worm testing allows sellers of sashimi grade tuna to certify it as worm-free and safe for raw consumption. If you catch your own tuna, microscope analysis provides peace of mind prior to eating it.

Can Proper Freezing and Cooking Kill Worms?

Freezing and cooking tuna to certain temperatures both effectively kill any worms present. Here are the proper procedures:

• For freezing, tuna must reach -4°F (-20°C) or below for 7 full days, or -31°F (-35°C) until solid, then stored at -31°F (-35°C) for 15 hours.

• Cooking tuna to an internal temperature of 145°F (63°C) for at least 15 seconds reliably kills both parasites and bacteria. Use a food thermometer to verify.

• Lightly searing tuna via methods like tataki does not cook the interior enough to ensure worms are destroyed.

• Home freezing methods may not kill as effectively as commercial flash freezing. When unsure, cook tuna thoroughly after freezing before consuming.

Following these validated freezing and cooking guidelines minimizes any health risks from worms in fresh tuna.

Myths vs. Facts About Tuna Worms

Given the queasiness-inducing idea of worms in tuna, some myths and misconceptions propagate. Here are the main facts versus fiction about tuna worms:

• Myth: All worms in tuna make you sick.

Fact: Many worms are harmless if consumed. Only certain species cause illness.

• Myth: Cooking tuna lightly eliminates worms.

Fact: You need high, sustained internal temperatures to reliably kill worms.

• Myth: Marinating or brining tuna kills worms.

Fact: Only proper freezing and cooking have proven effective.

• Myth: Sushi grade or flash frozen tuna have no worms.

Fact: These are just indicators tuna was properly handled to kill worms, not guarantees.

• Myth: You can see all worms with the naked eye.

Fact: Some worms and larvae are microscopic. Lab testing is needed to confirm their absence.

By getting the facts straight, you can make informed choices when preparing and consuming tuna while safely mitigating the risks posed by worms.

Tuna Worms Can’t Dampen This Nutritious Fish

While the notion of worms in tuna may be unpleasant, it’s simply a natural reality when eating wild fish. With care and common sense, you can still enjoy the immense benefits and delicious flavor of tuna without undue concern