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Expert: Salmon is as apart from rainbow trout like apple from pear

chinadaily.com.cn | Updated: 2018-08-16 14:33
A worker arranges fresh salmon as they pass along a conveyor belt at Salmar ASA's InnovaMar harvesting and processing facility on the island of Froya, Norway. [Photo/Agencies]

China is in midst of heated discussion over whether the China Aquatic Products Processing and Marketing Alliance was right in classifying freshwater rainbow trout as salmon. The opponents claim the freshwater fish might contain parasites that could harm humans.

Zhong Kai, a standing member of China’s preventive medical association body and a food safety expert, shares his views with China Daily’s Zhang Zhouxiang.

Q: Biologically, what is the relationship between salmon and trout?

A: The two kinds of fish are of the same family, namely the salmonidae family, but of different genus. Salmon belongs to the salmo genus, while rainbow trout belongs to the oncorhynchus genus.

The former lives in the ocean, so as the majority groups of the latter, but rainbow trout lives in freshwater. Their biological relationship is comparable to that of apple and pear.

Q: Why do doctors recommend not eating freshwater fish raw?

A: Because of parasites. Actually, both saltwater and freshwater fish can be infected by parasites, but saltwater has higher osmotic pressure, so even if the parasites infecting oceanic fish enter human bodies they will not grow.

Yet freshwater fish have similar inner environments with humans, which make it possible for parasites inside their bodies to grow in human bodies, too. That’s the main reason why it is not suggested not to eat freshwater fish raw.

Q: But parasites are a problem with saltwater fish. How to kill them without cooking?

A: In practice, people kill the parasites of salmon by freezing its meat for certain period, and different countries and regions have different standards on the freezing time. For example, the US requires salmon meat should be frozen for 15 hours in minus 15 degrees Centigrade.

Theoretically, freezing can kill the parasites in freshwater fish, too, but there is no public data about that. To be safe, it is better to cook freshwater fish before eating because high temperature can kill the parasites.

Q: Some claim that rainbow trout can be prevented from harboring parasites by feeding them certain food. Is that true?

A: Not all. Food is only one of the causes, because fish can get infected by parasites from other channels. It is necessary to control the water sources, not only food.

Q: In theory, how to detect parasites inside fish meat? What about in practice? Can freshwater fish businesses strictly detect them?

A: There are strict standards on detecting parasites inside freshwater fish, and the main one is to observe sliced fish meat with microscopes. However, medically freshwater fish are not recommended to be eaten raw. They detect parasites inside freshwater fish to protect the fish’s health, not for raw-eating purposes.

Q: Some say that rainbow trout is nutritious, too, just not fit for being eaten raw.

A: I agree. Rainbow trout is quite nutritious and if you cook them properly the flavor is good. Especially, when rainbow trout is raised by humans with professional feedstuff, it can be more nutritious than salmon. Whether to eat it raw depends on one’s personal choice and I do not recommend eating it raw.

Q: Do you have any advice for domestic rainbow trout businesses?

A: I think it is better for them to have their own brands, instead of trying to mix their products with salmon. Freshwater fish are the main fish products of Chinese people, and many believe eating fish helps people stay smart, which is a huge advantage for freshwater fish businesses, including rainbow trout companies.

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