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I was defrosting fish and forgot about it. It has been left out for a long time. How long can fish actually be left out before it goes bad?

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Someone can feel free to correct me if I'm wrong, but I'm 99% certain that the rules for fish are exactly the same as those for meat, which makes this a duplicate of Is it safe to cook a steak that was left out (raw) for 7 hours? It's not safe to leave out at room temperature for any length of time, let alone a "long time". –  Aaronut Oct 21 '11 at 17:07
    
possible duplicate of Is it safe to cook a steak that was left out (raw) for 7 hours? –  rfusca Oct 21 '11 at 18:34
    
@Aaronut Not a duplicate - rules for fish are different. Fish begins to deteriorate as soon as it leaves the water whereas stake can last for a much longer time without going bad. –  Bizorke Dec 20 '11 at 15:57
    
@Bizorke: Everything "begins to deteriorate" once it's dead. Can you back up the claim that it's any different from other kinds of meat with a source? And if so - might as well post an answer. –  Aaronut Dec 20 '11 at 19:15
    
@aaronut Alright I was actually just reading up on this a little while ago. I'll post what I found. –  Bizorke Dec 20 '11 at 19:29

4 Answers 4

up vote 3 down vote accepted

A quote from the below link;

"Do not thaw frozen seafood at room temperature. Thaw in the refrigerator or defrost in the microwave oven. If thawing in the refrigerator, allow one to two hours per pound of seafood".

http://www.uaex.edu/Other_Areas/publications/PDF/fsfcs100.pdf

&

Another quote from the link below;

"... If food is allowed to remain at room temperature for two hours or longer, bacteria can multiply and cause food poisoning. - Even a tiny amount of contaminated food can cause severe illness. If you have any doubt about the safety of the food, throw it out!"

http://www.calpoison.com/public/food.html

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Just wanted to add another experience: I left a piece of salmon at room temperature for about 20 hours a few days ago (yes, nearly a full day). I then cooked it normally, ate it, and I am still alive. It was 100% fine. According to all the comments I have read online I should be extra sick or dead by now... so don't be too scared.

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No, the comments don't say that you should be sick. They say that it is usafe, which is a very different matter. –  rumtscho May 6 at 21:21
    
If Russian roulette doesn't kill you the first time you pull the trigger, that doesn't mean it's safe to keep playing. –  sourd'oh May 7 at 15:40

I know the fish is long eaten or thrown away by now, but since the question is still open I'll post.

Defrosting requirements of raw fish is a little different than that of land-mammal meat. I'm sure that the growth of bacteria for meat and fish is about the same, but fish will actually deteriorate faster than the meat even in the absence of bacteria if exposed to air.

I would cook and eat meat that's been left out raw up to 2-3 hours (depending on room temperature). However I would not eat a fish that's been left out in a warm room for much more than an hour of being defrosted. Fish decays faster than meat. It was my understanding that fish decays faster in air than in water (I was always told to always defrost fish in the sink rather than the counter), however I couldn't find adequate references to back that up (see comments). Whether in the sink or on the counter, bacteria will probably spread at just the same rate as any meat once the fish is defrosted so the clock is ticking.

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The fish is not being destroyed by air, it is destroyed by its own enzymes (they are more active than meat at room temps, because the living temp of fish is lower). So while the "fish spoils quicker than meat" part is correct, the "it would be the same if defrosted under water" part isn't, at least when compared to meat defrosted at the same temperature. –  rumtscho Dec 20 '11 at 20:42
    
@rumtscho Ahh I see. It was my understanding that fish decays faster when left in the air. I looked around but could only find one reference for this, but it's in the context of long-term storage rather than defrosting: fishcooking.about.com/od/howtochoosefreshfish/qt/… In any case, I can edit my answer. –  Bizorke Dec 20 '11 at 21:09
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I don't have an online reference to link to, but just re-checked with On Food And Cooking. Page 189 in the 2004 UK edition (subsection The Perishability Of Fish) confirms that fish spoils quicker than meat because their enzymes and the bacteria living in/on fish are active even at low temperatures (5°C is "balmy" for them), while the analogues in warm-blooded animals "slow to a crawl" in a fridge. But he also mentions that fish oil oxidizes quicker than saturated fat, which isn't harmful, but I guess you can make an argument that it reduces the taste qualities of the fish. –  rumtscho Dec 20 '11 at 22:15
    
I'm not too happy with this about.com article - I find the idea that there is less flavor loss in frozen fish than in frozen meat suspicious. But the reason why they are so adamant against air is not so much oxidation in the raw fish as freezer burn in the frozen fish, as they admit in their third point. Which makes sense too, freezer burn is unpleasant on any kind of food. –  rumtscho Dec 20 '11 at 22:18
    
The reason's provided seem logical to me. But yea I agree that it's not the best source; the article itself would be a lot more credible with some references. It's written by an experienced seafood chef though. –  Bizorke Dec 20 '11 at 22:29

It depends what the ambient temperature is and exactly how long it's been left out. If it smells bad, looks a funny colour or is suspect in any way, throw it out - no amount of fish (or the money you paid for it) is worth a bout of food poisoning.

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Of course, this is only valid as a negative check. If it's visibly spoiled and/or odiferous then it's definitely bad. But if it smells and looks fine, that still doesn't mean it's free of (potentially severe) bacterial contamination. –  Aaronut Oct 21 '11 at 20:38

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