Why do freeze raw fish kill parasites?

Hi oem7110

The cold doesn't kill parasites, it prevents bacteria and other disease causing organisms from accumulating and growing out of control.

Do parasites still able to survive after changing body status from liquid (blood/fluid) to solid (ice)? Their internal structure should be total damaged, would it be correct?

Do you have any suggestions?
Thank you very much for any suggestions (^v^)
 

Some species have the ability to survive frozen. Also important that you define what you mean by parasite, because a parasite can be a microorganism and it can also be a large animal I'm assuming that you're referring to the former. The bacteria, Listeria, is one such organism

https://www.sciencedaily.com/releases/2013/10/131010124827.htm

Please see following video,

That video is disturbing

To answer your question, freezing does not kill parasites, it stunts or slows down growth, that's all.

Some video said in Chinese that ice crystal would cut parasites body into different parts during freezing period, so indirectly this approach would kill parasites, would it be correct statement?  

"In order to reduce the risk of parasites, control measures should be taken to freeze raw fish for -20 ° C or below for seven days; or to freeze at – 35 ° C for about 20 hours." That is Foods and Health Department suggests on handling raw fish for Sushi stores, that is reality.



Do you have any suggestions?
Thanks, to everyone very much for any suggestions (^v^)

That's possible, but what's more worrisome are the eggs these parasites lay. The eggs are resistant to very high and low temperatures.

Would ice crystal break the structure of parasites' egg as well?

After freezing an chick's egg on over 20 hours below -35 degree, can egg still grow into a chicken?

On another example, if human is frozen during the ice age, after melting ice, can human still survive?

Do you have any report on similar experience?
Thanks, to everyone very much for any suggestions (^v^)

Endospore-forming bacteria produce a unique resting cell called an endospore. Endospores can survive environmental assaults that would normally kill the bacterium. These stresses include high temperature, high UV irradiation, desiccation, chemical damage and enzymatic destruction. The extraordinary resistance properties of endospores make them of particular importance because they are not readily killed by many antimicrobial treatments.

This information relates to bacteria, though I don't think worms such as the one shown in the video can produce spores. They do produce eggs and have an intricate life cycle.

According to the FDA, freezing can kill parasites if the food gets cold enough and stays that way long enough. 

https://www.fda.gov/downloads/Food/GuidanceRegulation/UCM252393.pdf

For disease-causing parasites like tapeworms, roundworms and flukes, which may infest raw or undercooked fish, freezing can be the answer, but its effectiveness varies. It works best for tapeworms and appears to be somewhat less effective for roundworms and flukes. In general, killing parasites requires freezing and storing fish at a surrounding temperature of minus 4 degrees Fahrenheit or colder for seven days; or freezing at a surrounding temperature of minus 31 degrees or colder until the fish is solid and storing at the same temperature for 15 hours; or freezing at a surrounding temperature of minus 31 degrees until the fish is solid and storing at minus 4 degrees or below for 24 hours. Not all home refrigerator freezers get cold enough. 

The F.D.A. also warns that these techniques may not be suitable for particularly large fish, like those thicker than six inches.

I would like to know on how structure of water behavior different under minus 4 degrees and minus 31 degrees Fahrenheit.

Do you have any suggestions?
Thanks, to everyone very much for any suggestions (^v^)

Water expands at 0 degrees Celsius, this is why it damages cells since the cytoplasm of cells consists of water.

As the temperature of the water approaches -55 degrees F, the water molecules form tetrahedrons, with each molecule loosely bonding to four other molecules.



Link: https://biology-forums.com/index.php?action=gallery;sa=view;id=30240

More on this here: http://ergodic.ugr.es/termo/lecciones/water1.html

The most destruction force is ice's expansion, would it be correct? which damage the cell's internal structure, would ice's structure expand greatly as temperature drops lower? such as -55 degrees F, which cause more damage within cell's internal structure and that is why require less time to frozen raw fish.

Do you have any suggestions?
Thanks, to everyone very much for any suggestions (^v^)

I don't think it the expanding of cells that causes it to die. Under normal circumstances, the water crystals that form during freezing would destroy all organelles and membranes. So you're right about causing internal damage, but it's not the cell rupturing that's the issue.

You guys are assuming it's because of the increased volume, which is around 10% and easily sustainable for a flexible membrane. There are many invertebrates that can survive freezing, whether it be 0 degrees or -55 degrees Celsius (https://biology-forums.com/index.php?article=1428).