Is it true that marine fish can be eaten raw because they have no parasites?

The discovery of fire changed human ancestors from "eating raw food" to "eating cooked food". Even so, to this day, humans still love "raw food". For example, sashimi made from various seafood makes countless people salivate. So why must seafood be used to make sashimi, but not river fish? Why can sea fish be eaten raw, but river fish cannot?

When it comes to eating sashimi, we immediately think of Japanese food, but in fact the tradition of eating sashimi has a long history in my country. Legend has it that Chen Deng, the prefect of Guangling under Cao Cao during the Three Kingdoms period, had a special liking for sashimi. However, the sashimi Chen Deng ate was made from river fish, so a large number of parasites accumulated in his body. Thanks to Hua Tuo's superb medical skills, his life was saved. After that, Chen Deng abstained from eating for a while, but in the end he could not resist the temptation of sashimi, and he ate it unscrupulously again, and finally died of the disease three years later.

So, is it because marine fish have no parasites that marine fish can be eaten raw, but river fish cannot? Many people may think so, but this is not actually the case.

Parasites are not only found in freshwater fish, but also in marine fish. Whether it is caught marine fish or farmed marine fish, they are not immune. Therefore, marine fish can be eaten raw not because there are no parasites in their bodies, but because of another reason, which is osmotic pressure. The osmotic pressure principle is simply that water molecules always penetrate from high concentration to low concentration, and the concentration of seawater is completely different from that of freshwater. Therefore, in order to adapt to different living environments, the body functions of marine organisms and freshwater organisms are also completely different. Therefore, marine organisms cannot survive in fresh water, and similarly, freshwater organisms cannot survive in sea water.

That is to say, the parasites in marine fish cannot survive in the human body for a long time. However, some marine parasites can barely survive in the human body, but they cannot develop to maturity, such as the third-stage larvae of Anisakis.

Although the larvae of Anisakis cannot mature in the human body, it is still disgusting to think about them in the body! Don't worry, it is not difficult to kill them, just freeze them. Different countries and regions in the world have corresponding standards for freezing salmon before they are put on the market. According to these standards, salmon needs to be frozen at minus 18 to 25 degrees Celsius for 48 hours to a week before it can be put on the market. Marine parasites represented by Anisakis are not resistant to low temperatures, and freezing can kill them completely. Therefore, it is unsafe to slice and eat marine fish directly without freezing them after they are caught and brought ashore.

The reason why freshwater fish cannot be eaten raw is that the osmotic pressure in the human body is very different from that in freshwater, so freshwater parasites can survive for a long time once they enter the human body.

Take the most common freshwater parasite Clonorchis sinensis, also known as liver fluke, for example. Once it enters the human body, it can live in the body for up to 20 years. Freshwater parasites can survive in the human body for a long time, so can we freeze freshwater fish like marine fish? No.

The most common parasites in freshwater fish are liver flukes and lung flukes. Trematodes have a strong tolerance to low-temperature freezing and can revive once thawed. Therefore, even freshwater fish that have been frozen cannot be safely eaten.

Does this mean that freshwater fish cannot be eaten? Yes, they can be eaten. Whether it is marine parasites or freshwater parasites, heating is the best way to kill them, so as long as they are cooked, there is no risk of infection with parasites.