It is rumored online that a Japanese restaurant changed its statement and said that the selected fish species is rainbow trout. Is rainbow trout really salmon?

The new coronavirus was detected on the cutting board used to cut salmon at Beijing Xinfadi Market. There are rumors that a Japanese restaurant changed its words and said that the fish species used was rainbow trout. Is rainbow trout salmon?

Is rainbow trout a type of salmon?

If you go around the market, you will find that although many fish are called "salmon", there are many "prefixes" in front of these "salmon", such as Norwegian salmon, Alaskan salmon... and even "freshwater salmon". For example, Beijing Huairou, Yunnan Lijiang, and Sichuan Qingcheng Mountain all regard "freshwater salmon" as local specialties. Many places even advertise "caught alive and killed to your heart's content, the fresh taste beats frozen fish in seconds", and promote "one fish, multiple ways to eat", slaughtering and selling "freshwater salmon" sashimi on the spot.

There are so many "salmons" that it's hard to tell them apart! Generally speaking, in Chinese shopping malls, the so-called "salmons" can be roughly divided into Atlantic salmon, Pacific salmon, and freshwater rainbow trout. Atlantic salmon live in the North Atlantic Ocean in Norway, Denmark and other places, and migrate to rivers along the European coast every year to lay eggs. These fish will leap over waterfalls and swim upstream when migrating, so Europeans a long time ago called them "salmo" (meaning "rise") in Latin. Later, the word gradually evolved into "salmon". This fish is one of the important fish caught along the northern coast of Europe.

▲In the 17th century, people were fishing for Atlantic salmon on the Seine River in France (Photo from the Internet)

The production of Atlantic salmon has been increasing year by year, and merchants along the Atlantic coast have begun to sell this fish to other countries, including China. As for why Atlantic salmon is called "Salmon" in China? It is said that this name can be traced back to the 1970s when Atlantic salmon was introduced to Hong Kong. It was translated into "Salmon" based on the common name of Atlantic salmon in Europe, which was "salmon". It is mainly based on Cantonese transliteration, and because the fish meat has many stripes, the name "Salmon" is translated very cleverly. It must be pointed out that the Chinese "Salmon" refers to Atlantic salmon, not other salmonids!

Later, several types of fish that looked similar to "salmon" and would migrate and lay eggs were discovered along the coasts of Japan and Alaska in the Pacific Rim, so they were all called "salmon". In order to distinguish them, people called the salmon from Europe "Atlantic salmon" and the newly discovered "Pacific salmon", or Pacific salmon.

Later, with the development of aquaculture, the breeding and fishing of Pacific salmon also gradually emerged, and the export volume also increased rapidly. However, how to make these Pacific salmon seize the market that originally belonged to Atlantic salmon has become a problem. So some savvy Chinese businessmen took advantage of the fact that many Pacific salmon also have the word "salmon" in their English names and named them after the familiar "Salmon". As a result, Pacific salmon also share the name "Salmon", and ordinary consumers cannot tell the difference. The salmon, taimen, and whitebait in the Heilongjiang, Yalu, and Tumen River basins of China are cousins ​​of salmon, with similar lifestyles and habits. The Chinese are already familiar with them and their appearance is quite different, so merchants dare not use the name of salmon.

▲At Brooks Falls in Alaska, a Pacific salmon jumps straight into the mouth of a waiting brown bear. (Photo by Chris McLennan, New Zealand photographer)

The "salmon" that CCTV is reporting is farmed in Qinghai-Tibet, China, is rainbow trout. It is a cold-water pond fish of the genus Pacific salmon in the family Salmonidae. Rainbow trout is an important cold-water fish that is widely farmed in the world. It is named because mature individuals have a brown-red vertical stripe along the lateral line that looks like a rainbow. It is native to northern North America and the west coast of the Pacific Ocean. It mainly lives in low-temperature freshwater and has high requirements for the water quality of the breeding waters.

▲ Pacific salmon genus of the Salmonidae family - rainbow trout (picture from the Internet)

In the consumer market, when Europeans say "salmon" and Chinese say "salmon", they both refer to a type of fish in the salmon family, especially several salmonids in their own country. Norwegians mainly refer to Atlantic salmon as "salmon", and Americans call Atlantic salmon and Pacific salmon "salmon". Chinese usually call salmon, taimen, and whitebait salmon, and call Atlantic salmon and Pacific salmon "salmon". Rainbow trout also belongs to the salmon family in biological classification, but usually rainbow trout has always been called rainbow trout. The academic and industry circles have long known it, and no one has ever called it "salmon". So why can rainbow trout be called salmonid but not "salmon"? Because at that time, the translation of "salmon" into "salmon" specifically referred to Atlantic salmon, which means that the Chinese "salmon" is not equivalent to the English "salmon".

Are freshwater fish more likely to carry parasites?

As for the parasite problem of freshwater fish pointed out by many comments, in fact, both freshwater and marine fish may become the natural intermediate hosts of certain parasites (the final host is mammals such as humans). Moreover, the parasites in freshwater fish are relatively serious. Many parasites are from the phylum Nematodes and Platyhelminthes, such as trematodes. Trematodes are more likely to breed in freshwater fish and shrimp. This is because these small creatures are easily bred in the silt of freshwater fish ponds and pools, and most people are susceptible to parasites. They are more adapted to the freshwater quality of rivers, lakes and reservoirs. Seawater contains higher salt content and high osmotic pressure, which is not suitable for the growth of such parasites.

Generally speaking, parasites in seawater are less harmful to the human body than freshwater fish because their living environment is quite different from that of the human body. This is related to the osmotic pressure of fish body fluids.

The freshwater environment in which freshwater teleosts live is a hypotonic solution relative to their cells, so they absorb water with their gills and skin, excrete water with their kidneys, and replenish salt through salt-absorbing cells and food. The osmotic pressure of their body fluids is not high. Seawater is a hypertonic solution relative to their cells, so marine fish absorb seawater and then excrete salt through salt-secreting cells and other pathways. The osmotic pressure of marine fish body fluids is relatively high.

Parasites living in fish will adapt to the osmotic pressure of fish body fluids. The osmotic pressure of freshwater fish body fluids is closer to that of terrestrial humans, so freshwater fish parasites are more likely to survive in the human body. However, marine fish parasites cannot survive in the human body for a long time.

Most of the main parasites in marine fish are Anisakis, including salmon (Atlantic salmon), king salmon, tuna, sea bass, cod, hairtail...even squid, which is not a fish, may be infected. However, even if you accidentally eat sashimi containing Anisakis, you don't need to worry too much, the harm is not that great. Because the human environment is not friendly to it, the most serious manifestations are gastrointestinal discomfort, nausea, vomiting, diarrhea, abdominal pain, etc. Anisakis can only survive as larvae in the human body for a few weeks and die before developing into adults, so the harm is relatively small.

How to eliminate parasites in fish?

Rainbow trout is a freshwater fish. Freshwater fish and shrimp may carry a variety of parasites, such as Diphyllobothrium latum, Pulmonary liver fluke, Gnatostoma nematode, etc. No matter how clean the lake water is, there are various parasites in the mud and sand at the bottom of the pond. No matter how clean the water is and how good the water quality is, there will be parasites. The quality of water is not the decisive factor in the number of parasites in fish. In fact, in some waters where pollution is more serious, there are fewer parasites, which makes many aquatic experts wonder whether parasites also like "comfortable" environments? As for avoiding parasite infection sources by controlling feed, the effect is not very good, because humans cannot control fish from eating natural bait in lake waters.

Whether freshwater or marine fish, whether it is Japanese Pacific salmon, Norwegian Atlantic salmon, or Chinese rainbow trout, there is a risk of parasites. Freshwater fish have a wide variety of parasites, and they are more likely to parasitize the human body. The risk of infection is very high if eaten raw. Once infected, it may even invade the brain, which is very dangerous. Similarly, marine salmon (Atlantic salmon, etc.) may also be at risk of infection with parasites such as Anisakis.

Some people say that eating salmon raw with mustard, vinegar, white wine, mashed garlic or ginger can kill parasites? According to the results of the "Test on the Tolerance of Simple Anisakid Larvae to Condiments, Antihelmintics and Traditional Chinese Medicines" published by the Medical College of Yanbian University in 2001, Anisakids can survive for 105 hours in vinegar, 24 minutes in high-concentration white wine, 7 hours in mashed garlic juice, and 10 hours in ginger juice.

According to the "Survey on Anisakiasis Infection in Fishes in the East China Sea and Study on the Tolerance of Larvae to Green Wasabi" published by Ningbo Center for Disease Control in 2006, soaking in mustard for 55 minutes can kill Anisakiasis. Even if you dip it in soy sauce, vinegar, mustard sauce, or drink white wine, it is not enough to kill these parasites.

▲An Atlantic salmon fishery in Iceland (Photo from the Internet)

So can salmon still be eaten raw? Of course, because salmon is processed by high temperature or freezing. In order to maintain the taste of fish, it is currently mainly frozen. In order to ensure that raw fish will not cause human diseases, the United States and some European countries have issued food safety regulations, stipulating that fish must be pre-processed to kill the larvae of Anisakis.

The U.S. Food and Drug Administration (FDA) stipulates that fish must be frozen at minus 35 degrees for 15 hours, or minus 20 degrees for 7 days before it can be eaten, while the EU standard is to freeze it at minus 20 degrees for more than 24 hours.

The parasites that salmon are susceptible to have complex biological structures and are very sensitive to cold and heat. Once they are frozen, they will be killed. Generally speaking, the risk of parasites is very low after freezing, and fresh ones may have live parasites. For food safety, don't pursue the "fresh" taste when eating salmon sashimi, and don't eat "freshly slaughtered" freshwater rainbow trout fillets raw.

If you really want to choose salmon with "authentic origin", you should choose Atlantic salmon that is farmed in pure seawater in Norway, Denmark, Iceland, Chile and other regions. It should be frozen to kill insects and basically eliminate the harm of parasites, so it can be safely eaten raw or half-cooked.

If the cutting board is found to contain COVID-19, can we still eat salmon?

So far, there is no evidence that the new coronavirus is directly transmitted through eating and drinking, and it is mainly transmitted through contact. If it is cooked food, of course there will be no problem. If it is raw, the risk is a little bit greater because the virus has a little more chance of contacting the mucous membrane.

The coronavirus can survive on surfaces for a few hours to a few days. Fresh salmon is airlifted and protected by a low-temperature environment, so it is theoretically possible that it could survive. Although the probability is not high, considering that once an epidemic occurs, the cost of prevention and control will be extremely high, the country may control such products in the near future.

For individuals, the probability of contracting COVID-19 by eating raw salmon is extremely low, but this is a completely unnecessary risk. To be safe, I suggest that everyone should not eat raw salmon or other imported fresh food recently, and wait for the results of the official investigation in the next two days before making a decision.

If the inside is half-cooked when frying, it should be fine, because it is only contaminated on the surface. If you insist on eating it raw, at least rinse the surface with running water.

Can "freshwater salmon" rainbow trout be eaten?

Although the fish farmed in the Qinghai-Tibet Plateau of China is freshwater rainbow trout, not the real "authentic" Atlantic salmon, and eating it raw is very risky, this does not mean that it is not a "good fish" or that it cannot be eaten. Rainbow trout is also a particularly good edible fish, suitable for most cooking methods (except eating it raw). It has the unique flavor of salmon, a high fat content, a delicate texture and chewy meat, and is especially suitable for frying and grilling, so as long as it is fully cooked, it can be eaten with confidence.

▲Spicy grilled rainbow trout with good color, aroma and taste (Picture from the Internet)

Zhou Zhuocheng, chairman of the Aquatic Biology and Aquatic Ecology Committee of the China Fisheries Association, pointed out that "the fish cultured in the Longyangxia Reservoir in Qinghai are triploid rainbow trout, which are fat and plump, and their meat quality is comparable to Norwegian salmon."

From a nutritional perspective, for example, when it comes to DHA, which is of most concern to everyone, there is not much difference between rainbow trout and salmon. Considering that rainbow trout is cheaper, you can eat more with less money and get more DHA. In addition, the "tycoons" always eat Norwegian and Danish salmon. Switching to rainbow trout is equivalent to increasing food diversity from the perspective of nutritional balance, which is also good for helping us get nutrition. So you can still eat rainbow trout with confidence, provided that it is cooked.

How to distinguish between rainbow trout and Atlantic salmon?

As mentioned before, salmon is not a scientific name, but a general term for a "commodity" in the Chinese market. Whether it is rainbow trout or Atlantic salmon from Norway, they are all collectively referred to as "salmon" in the industry. But if you are really a "senior foodie" and must eat Atlantic salmon and salmon, how should you distinguish them?

Note that farmed rainbow trout and Atlantic salmon are difficult to tell apart with the naked eye after they are filleted, so you can only tell by looking at the whole fish or buying from a reliable source. In summary, you can tell the difference based on price, whole fish, and fillets.

1. Price: Rainbow trout is a freshwater fish, and its price is only half of salmon. It is recommended to buy it from regular supermarkets, markets and other channels, and don't buy it if it is too cheap; if you want to eat it, try to eat it in a big restaurant, not in an unknown small shop; many friends are used to buying salmon online, which is fresh, convenient and cheap, but it is recommended to buy it with caution, especially in some popular sashimi shops, where the prices are ridiculously low, so it is recommended that you don't be greedy for cheapness.

2. Whole fish: Whole salmon and rainbow trout are easy to distinguish, as rainbow trout has a red line on its body. Salmon is usually over 1 meter long and weighs over 12 pounds, while rainbow trout is much smaller, about 40 centimeters long and weighs about 8 pounds.

3. Fish fillet: It is difficult to distinguish the fish meat after cutting, and you can only rely on the experience of "experienced foodies". If you look closely, there are some differences between rainbow trout and salmon. The color of salmon is a more conspicuous orange or dark red, while the color of rainbow trout is lighter. The fat layer between salmon muscles is usually clear and thick, especially in the belly of salmon, while the pattern of rainbow trout is not obvious.

(Part of the content comes from the WeChat public account "Dietary Reference")

Text/Reporter He Cong Photo Editor/Chen Yongjie

New Media Editor/Chen Xuanzhi

Interview and review experts:

Chen Shunsheng (Director of the Department of Aquatic Product Processing and Storage Engineering, School of Food Science and Engineering, Shanghai Ocean University)

Xu Hao (PhD, Yellow Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences)

Produced by: Science Central Kitchen

Produced by: Beijing Science and Technology News | Science Plus Client

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