Try mixing hoisin or miso into low-sodium soy sauce.
From one of my favorite bloggers, Smitten Kitchen , "I often see low-sodium soy sauce suggested as an alternative
but I’m
not convinced it’s a fair swap.
There’s something more caramelized and fermented in the fish sauce that you’d miss.
If you feel like playing around, I might whisk some additional hoisin or even miso into that soy sauce for a more complex flavor."
cooking.stackexchange.com/users/364/JustRightMenus
If you cannot have fish at all, try using grated Parmigiano Reggiano.
Fish sauce has two basic flavors: a sweeter one that is similar to Reggiano and a stronger one that is similar to cooked broccoli.
If I were to experiment, I would try a mixture of the two, with maybe some of the juice made from the inside pulp of tomatoes (the gel-like thing with the seeds).
cooking.stackexchange.com/users/183/papin
You should look into vegetarian fish sauce .
If you can't find it, but can find a vegetarian (anchovy-free) Worcestershire sauce, that will provide some of the flavour, though we haven't tried it with Thai food. :-)
A salty chicken bouillon might also do the trick in a pinch.
cooking.stackexchange.com/users/96/Chris Jester-Young
Seaweed and lemon juice, that's what I'm using right now.
I was just using the seaweed because I like it, was using lemon juice and soy sauce as the fish sauce replacement, but am pleasantly surprised that seaweed is providing that fish sauce flavor.
cooking.stackexchange.com/users/24667/Egan
http://thegentlechef.com/blog/?p=1563
This briny infusion is rich in “umami” (a loanword from the Japanese which can be described as a “pleasant savory flavor”) and can be used in equal amounts as a replacement for traditional fish sauce in your favorite Southeast Asian recipes.
This recipe yields about 1 cup.
Ingredients
2 cups water ¼ cup tamari, soy sauce or Bragg Liquid Aminos™ ½ medium onion, chopped 3 cloves garlic, crushed 2 T (4 g) dried shredded wakame (seaweed)
1 oz (28 g) dried shiitake, porcini or portabella mushrooms 1 tsp whole black peppercorns 2 T mellow white miso paste - Technique Bring all ingredients except for the miso to a boil in a small saucepan.
Cover, reduce the heat to a vigorous simmer and cook for 30 minutes.
Remove from the heat and let cool.
Mix the miso into the macerated mixture.
Strain the mixture through a fine mesh sieve into a glass jar, pressing the solids with the back of a spoon to extract as much liquid as possible.
Seal and refrigerate until ready to use.
Due to its salt content, this sauce should stay fresh for several months in the refrigerator.
cooking.stackexchange.com/users/36216/Jenni Greenfield
You can safely leave out the fish sauce without attempting to replace it with anything.
First of all, it's really more fishy than salty, so substituting soy sauce often makes your dish too salty.
Secondly, most curries or stews only call for a small amount of fish sauce and there are such wonderful things going on spice-wise in Thai cuisine that you really don't miss it.
cooking.stackexchange.com/users/359/goblinbox
Conimex makes a sweet, thick type of soy sauce called Ketchup Manis or Ketchup Bentang which we use a lot for marinades (pork, chicken satays etc)
I love it put a little in fried rice, lo meins too.
Yum!
you can find it in some specialty food stores, Thai/asian sections and Asian food stores and online.
cooking.stackexchange.com/users/19170/Bridget Bryant
I've tried Bragg Liquid Aminos sauce which is saltier, less sweet and also tangier then regular soy sauce.
I think its flavor also resembles fish sauce better than soy and it worked well with the dish I made (green papaya salad).
According to its label, it's made with NON-GMO soybeans and purified water.
And it's also not fermented or heated and Gluten-Free.
cooking.stackexchange.com/users/19221/Janet
You will lose a lot of the other flavors, but just using MSG can compensate for the strong umami and salty flavors present in fish sauce.
We use this substitute often as we find the fishyness of fish sauce unpleasant.
cooking.stackexchange.com/users/21555/Eric G
Your best bet is a light soy sauce, that, at least, will provide the 'saltiness'
If you need a fishy flavor you could always add a little fish paste or perhaps a fillet from a tin or bottle of fish, such as anchovies.
Just 'wizz' the two in a blender for a few minutes.
cooking.stackexchange.com/users/115/Pulse
You could use a smaller amount of oyster sauce if the person was only allergic to fish...
(But keep in mind that some oyster sauces also include fish sauce, so check carefully!).
That said, if the person is also allergic to oyster sauce (as your question states), then I'd probably subtitute it with some stock instead, perhaps a small amount of soy sauce, and add less sugar, because it will also be sweeter.
cooking.stackexchange.com/users/2699/Arafangion
I don't believe there is a substitute for fish sauce.
Soy sauce is completely different.
If using as a dipping sauce substitute , use soy sauce mixed with vinegar and sugar.
Another option is soy sauce mixed with fermented soybean paste, sugar, vinegar, chili pepper and water for dipping things like Vietnamese spring rolls.
Another alternative would be lime juice with soy sauce and sugar to dress a salad.
If cooking, I would use salt with a little MSG.
MSG adds Umami that can't be achieved even with fish sauce.
Worcestershire sauce is totally different from fish sauce.
Spices in it are too overpowering.
Hope that helps.
cooking.stackexchange.com/users/24295/Southwest
I cook with a vegetarian pho from my Vietnamese mother-in-law, who is the real deal!
It calls for no fish sauce and instead calls for 1/2 c. soy sauce and 1 Tbsp.
sugar in the broth.
It's delicious!
Maybe that's the substitute for fish sauce.
cooking.stackexchange.com/users/25449/vanessa
Are there any good substitutes for Fish Sauce for cooking Thai food?   This is due to a severe food allergy (anaphylaxis) to all forms of seafood, so I'm unable to substitute for other fish-based products.
What is a good substitute for Fish Sauce?
cooking.stackexchange.com
<substitutions><fish><asian-cuisine>
cooking.stackexchange.com/questions/1366
cooking.stackexchange.com/users/503/Todd Hunter
Soy sauce, vegetarian fish sauce or liquid aminos can add some of the saltiness and taste of fish sauce. Alternatively, grated Parmigiano Reggiano, salty chicken bouillon, seaweed and lemon juice or MSG can add a similar flavour. While it is possible to buy a vegetarian fish sauce, you can also try hoisin, miso or soy sauce as replacements.
Try hoisin or soy sauce as a replacement. Try parmesan cheese. Yo can find vegetarian fish sauces. Other options such as seaweed and lemon juice, chicken stock or MSG are also possible.