Time and temperature required to kill parasites in fish?

Question

There's a lot of incomplete information floating around the internet about food safety with regards to fish, sous vide, and sushi.

For example, plenty of sources say that cooking at 60C / 140F for 1 minute will kill Anisakis (a common parsite in salmon, and probably other fish as well).

Another source shows that a tapeworm called Diphyllobothrium can be killed by cooking at 55C / 131F for 5 minutes.

But they don't provide a range of times and temperatuers for pasturization. As far as I know, cooking times for food safety are always a function of both time and temp, so there should be more information than this.

Meanwhile, I've found a lot more information about killing bacteria on fish rather than parasites. This popular sous vide guide presents a pasturization chart for seafood with regards to bacteria, and the author suggests using those same numbers to deal with parasites like anisakis as well. This would suggest that killing bacteria and killing parasites is a roughly similar process, but I haven't found any other source to confirm this. Also, that guide's chart tells you how long to cook the food in a sous vide bath — it doesn't tell you how long to hold the food at a given temperature to pasturize it, so it won't really help if you're pan cooking.

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So, does anyone know if this has been researched before? Do you think you can kill anisakis with 5 mins at 131F?

I ask this because, in terms of culinary quality, fish at 130F tastes a lot better than 140F or 145F. And from what I understand, killing off parasites is important for nearly all* fish, not just salmon. Home freezers don't go low enough to kill parasites, and I think that's why the official guidelines always tell you to cook to 145F. Granted, I've routinely eaten fish at 130F-135F, but I never really confirmed if this was safe or not.

At the same time, I've also eaten pork chops at 135F plenty of times, while the tapeworm Trichinella doesn't die until 60C / 140F for one minute. But I think this is more impacted by farming practices than anything else (i.e. the number of pigs infected with tapeworms has probably decreased over the years with changes in farming practices, but this may not be true for wild-caught fish).

* I've heard that farm-raised salmon are less likely to be infected with parasites than wild-caught, but I can't find a source right now

tl;dr I've been unable to find a time-temp pasturization chart for parasites (not bacteria) in fish — and due to the prevalence of parasites in fish (compared to beef/pork/chicken), I can't figure out if it's reasonably safe to eat fish at 130F or 135F, even though most cooks probably do this regularly.

Answer 1

Anisakis is a tough parasite. According to the CDC you have to cook to 145°F/63°C to instantly kill Anisakis parasites, not 60°C. This study I found has a great deal of information about fish parasites, according to it a 3cm salmon fillet needs 10 minutes at 60°C to be fully safe. Between the two I'd probably cook it to 63°C and get it off the heat.

I could not find a distribution curve for Anisakis versus cooking temperature, there were citations on the study to other papers that could be relevant but they don't seem to be available on the web. There's plenty about freezing, and according to the CDC a week at -f°F/-20°C is enough to kill it, and that's do-able in most home freezers, as long as you carefully monitor it to make sure it's hitting that temperature.

From a heat perspective, looking at other parasites gives an idea of how long it takes to kill. Trichinella needs 2 minutes at 60°C, 6 minutes at 131°F/55°C, and 6 hours at 120°F/49°C. As Anisakis takes 10 minutes at 60°C we can extrapolate it will require much longer to kill it at lower temperatures, using 5X as a guide you'd need 30 minutes at 55°C and 30 hours at 49°C, but that's simplistic, without data we just don't know. An hour at 131°F/55°C is probably more than sufficient, the key word is probably. So if you've got some wild fresh salmon and you want to cook it to 131°F sous vide you're probably fine as long as you keep it at a high enough temperature long enough, you just need to be aware of the risks.

However, it's probably not a problem you need to worry about. 85% of the 'fresh' fish we eat is actually frozen on the boat, then shipped and thawed before being packaged and sold as 'fresh', this is because fish goes bad so quickly there's no other way to get it from the ocean to inland stores fast enough. So if you want to cook it to 131°F/55°C sous vide without worry your best source of fish is the freezer section.