An Ontario biology professor and her class found stomach-turning results after they tested the DNA of fish samples from sushi restaurants and grocery stores across the province.

So on Friday my Molecular Bio students did a lab about fish fraud. Their Super Important Homework Assignment (TM) was to go out for sushi and take a small sample home in a ziploc bag (EAT THE REST. Wasting food is uncool). Label the supposed fish, put it in the freezer. — Dr. Jen M (@AwesomeBioTA) April 1, 2019

Fanshawe College Prof. Jennifer McDonald said the exercise, which mirrors testing done by food safety officials in the U.S. and Canada on products like olive oil and maple syrup, had be useful to her molecular biology students in London, Ont. Watch: The scope of fish fraud goes beyond just Canada. Story continues after the video. "It is the type of experiment that is not only interesting and relevant to everyday life, but also relevant to their lives as laboratory technicians when they [graduate]," she told HuffPost Canada via email. The class sent nine different samples to a lab to look for fish fraud. The results: only two samples actually were actually the fish they were supposed to be.

OH BOY OH BOY. I just got the results back from my class' foray in sequencing fish samples. ARE YOU READY? They're a mind-bender. https://t.co/O7yBCHEQg4 — Dr. Jen M (@AwesomeBioTA) April 5, 2019

Even more disturbing? One of the samples — fresh salmon from a grocery store — tested positive for body louse — a tiny insect that can spread disease and consumes dead human skin and blood.

This wasn't a piece of garbage from a market. This was from a "salmon fillet" that someone paid good money for, cut some off before they cooked it, put it in saran wrap & brought it in. BODY LOUSE. Think about how much there must be in that sample to override fish DNA! — Dr. Jen M (@AwesomeBioTA) April 5, 2019

McDonald documented the experiment in a Twitter thread. Mislabelled fish included: Tilapia, which is a white fish, was being passed off as red tuna, which suggests it was dyed

Rainbow trout actually being coho salmon — a more expensive fish

Atlantic cod — a threatened fish species — being labelled as Pacific cod

Rainbow trout labelled as Atlantic salmon

Escolar, which contains an indigestible oil that can have a laxative effect on humans, was being called white tuna.

Boston Globe via Getty Images Albacore tuna, left, and escolar, right.

Escolar has been banned in Japan since 1977, but can be sold legally in Canada as long as it is correctly identified since "it does not pose a health risk to consumers," according to the Canadian Food Inspection Agency.

Reena sequenced what was labelled (on the box I bought at the grocery store, no less) Icelandic Cod (MSC-certified). It was. Thank God. Sydney sequenced what was labelled (again, ON THE BOX purchased at the grocery store) Pacific Cod. It was Atlantic Cod. (CRINGEEEE!!!!!!) — Dr. Jen M (@AwesomeBioTA) April 5, 2019

Evalyne sequenced the other sample of "white tuna". That was the one that I brought in, that I theoretically would have eaten if I actually liked and ate "white tuna" (I think it's gross). It was escolar. THIS IS DANGEROUS. Can cause extreme gastrointestinal distress. — Dr. Jen M (@AwesomeBioTA) April 5, 2019

The only two samples that came back correctly labelled were rainbow trout and Icelandic cod. "I knew about fish fraud as existing, but I wasn't aware of just how big of a problem it really is," McDonald told CTV News. She also told HuffPost Canada that the seafood industry wasn't the only culprit. "I hope that this starts to make people more aware about what they're eating... there are many other food products that may not be what they claim they are! I think we, as consumers, need to demand more oversight on the food supply chain not just in Canada but around the world." Wider implications McDonald said the results have serious implications for people with food allergies or people who avoid certain foods for cultural or religious reasons. "As consumers, we do the best we can to avoid foods that we know are going to make us sick (or, in some cases, kill us) but if we can't trust the label or the menu, how can we know that the food we're eating is safe for us before it's too late?" she said. She pointed to imitation crab as an example, which contains gluten and could be dangerous for people with a gluten intolerance or allergy. Imitation calamari, which is made of pig anus, could be inadvertently eaten by those who don't eat pork products meat for cultural or religious reasons, she said.

Getty Creative Salmon fillets.