I bought some prawns yesterday at a supermarket. Although displayed on the fish counter with fresh fish, they were clearly frozen or partially frozen. I put them in the fridge over night.

Today, I've noted they've turned black. After a little research, it shows this could be due to oxidation, although others have commented they've never seen this before even if they've worked in "the" industry.

And one comment suggested that any black on prawns means they're spoiled and should be binned/destoryed. This is the part I'm sure of.

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I have tried to wash with running water and can't remove this black colour.

There is no unexpected odour.

Sadly, I've also noted that the squid which I bought has released its link. Although all this fish was in the same outer bag, the squid was it its own bag and it doesn't appear to have leaked.

After taking the shell off, there isn't really any colouration to the flesh.

Is is possible to know if they are safe. Is this a known thing - that prawns turn black and it means either oxidation or that they're spoiled?

  • Were these prawns supposed to be raw or cooked when you purchased them? If they were supposed to be raw, they may have gotten too warm or hot somewhere along the way, as they look cooked.
    – Cindy
    Commented Jul 26, 2017 at 14:01
  • @Cindy, this is how they looked when I bought them. I agree, they do look a little cooked, but they were in a freezer bag for a 25 minute drive. The day wasn't dreadfully hot at about 28C. I guess this shows the problems with pictures... To be honest, I've not eaten them and gave them back to the sea. However, I think the question remains valid?
    – Dave
    Commented Jul 26, 2017 at 18:15
  • 1
    If that's how they looked when you bought them (a little cooked), it's possible that they got too hot somewhere in the distribution chain, possibly even before they got to the supermarket where you bought them. I think you were wise to give them back to the sea. And yes, I think the question is still valid as the black wasn't there when you bought them. Someone may have experienced something similar or be able to confirm what the black color actually is.
    – Cindy
    Commented Jul 26, 2017 at 19:05

1 Answer 1


They look like they have been blanched. Or dipped in boiling water. The red.This is some times done if they have parisites on them. But froze? & shipped? I am talking about prawn fresh of the boat at home. Then blanched & froze at home for later use. I would avoid these if store bought. If I did not know they were boat fresh. How handled. Many prawn & shrimp are black in color. But not like that.

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